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Encyclopedia > C (programming language)
C
Paradigm imperative (procedural)
Appeared in 1972
Designed by Dennis Ritchie
Developer Dennis Ritchie & Bell Labs
Turing-complete Yes
Typing discipline static, weak
Major implementations GCC, MSVC, Borland C, Watcom C
Influenced by B (BCPL,CPL), ALGOL 68[1] , Assembly, PL/I, FORTRAN
Influenced awk, csh, C++, C#, Objective-C, BitC, D, Java, JavaScript, Limbo, Perl, PHP, Python

In computing, C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system.[2] A programming paradigm is a fundamental style of computer programming. ... In computer science, imperative programming, as opposed to declarative programming, is a programming paradigm that describes computation in terms of a program state and statements that change the program state. ... This article is about the computer programming paradigm. ... Dennis MacAlistair Ritchie (born September 9, 1941) is an American computer scientist notable for his influence on C and other programming languages, and on operating systems such as Multics and Unix. ... For other uses, see Software developer (disambiguation). ... Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ... For the usage of this term in Turing reductions, see Turing complete set. ... In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ... In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ... In computing, weak typing, when applied to a programming language, is used to describe how the language handles datatypes. ... Look up Implementation in Wiktionary, the free dictionary. ... The GNU Compiler Collection (usually shortened to GCC) is a set of programming language compilers produced by the GNU Project. ... Visual C++ 6. ... Turbo C was a Borland Integrated Development Environment and compiler for the C programming language. ... The Watcom C/C++ compiler is esteemed amongst DOS developers by the high execution speed of the compiled code it produces and for having been one of the first compilers to support the Intel 80386 protected mode. In the mid-1990s, some of the most technically ambitious DOS games such... B was the name of a programming language developed at Bell Labs. ... BCPL (Basic Combined Programming Language) is a computer programming language that was designed by Martin Richards of the University of Cambridge in 1966; it was originally intended for use in writing compilers for other languages. ... The Combined Programming Language (CPL) was a computer programming language developed jointly between the Mathematical Laboratory at the University of Cambridge and the University of London Computer Unit during the 1960s. ... ALGOL 68 (short for ALGOrithmic Language 1968) is an imperative computer programming language that was conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and a more rigorously defined syntax and semantics. ... An assembly language is a low-level language for programming computers. ... PL/I (Programming Language One, pronounced pee el one) is an imperative computer programming language designed for scientific, engineering, and business applications. ... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ... This article is about the programming language. ... The C shell (csh) is a Unix shell developed by Bill Joy for the BSD Unix system. ... C++ (pronounced ) is a general-purpose programming language. ... C# (see section on name, pronunciation) is an object-oriented programming language developed by Microsoft as part of the . ... Objective-C, often referred to as ObjC or more seldomly as Objective C or Obj-C, is an object oriented programming language implemented as an extension to C. It is used primarily on Mac OS X and GNUstep, two environments based on the OpenStep standard, and is the primary language... BitC is a programming language currently being developed by researchers[1] at the Johns Hopkins University, as part of the Coyotos project. ... For other programming languages named D, see D (disambiguation)#Computing. ... Java language redirects here. ... JavaScript is a scripting language most often used for client-side web development. ... Limbo is a programming language for writing distributed systems and is the language used to write applications for the Inferno operating system. ... For other uses, see Perl (disambiguation). ... For other uses, see PHP (disambiguation). ... Python is a general-purpose, high-level programming language. ... For the formal concept of computation, see computation. ... In computer programming, a statement block (or code block) is a section of code which is grouped together, much like a paragraph; such blocks consist of one, or more, statements. ... This article is about the computer programming paradigm. ... In computer science, imperative programming, as opposed to declarative programming, is a programming paradigm that describes computation in terms of a program state and statements that change the program state. ... A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. ... Dennis MacAlistair Ritchie (born September 9, 1941) is an American computer scientist notable for his influence on C and other programming languages, and on operating systems such as Multics and Unix. ... Bell Telephone Laboratories or Bell Labs was originally the research and development arm of the United States Bell System, and was the premier corporate facility of its type, developing a range of revolutionary technologies from telephone switches to specialized coverings for telephone cables, to the transistor. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... An operating system (OS) is a software that manages computer resources and provides programmers with an interface used to access those resources. ...


Although C was designed for implementing system software,[3] it is also widely used for applications. It is widely used on a great many different software platforms and computer architectures, and several popular compilers exist. System software is a generic term referring to any computer software which manages and controls the hardware so that application software can perform a task. ... Application software is a subclass of computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform. ... In computing, a platform describes some sort of framework, either in hardware or software, which allows software to run. ... A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... This article is about the computing term. ...


C has greatly influenced many other popular languages, especially C++, which was originally designed as an extension to C. C++ (pronounced ) is a general-purpose programming language. ...

Contents

Philosophy

C is an imperative (procedural) systems implementation language. Its design goals were for it to be compiled using a relatively straightforward compiler, provide low-level access to memory, provide language constructs that map efficiently to machine instructions, and require minimal run-time support. C was therefore useful for many applications that had formerly been coded in assembly language. In computer science, imperative programming, as opposed to declarative programming, is a programming paradigm that describes computation in terms of a program state and statements that change the program state. ... This article is about the computer programming paradigm. ... Systems programming (or system programming) is the activity of programming system software. ... This article is about the computing term. ... In computer science, runtime or run time describes the operation of a computer program, the duration of its execution, from beginning to termination (compare compile time). ... An assembly language is a low-level language for programming computers. ...


Despite its low-level capabilities, the language was designed to encourage machine-independent programming. A standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with minimal change to its source code. The language has become available on a very wide range of platforms, from embedded microcontrollers to supercomputers. In Computer science, a machine-independent program is any program that can be run by any computer, without regard to its architecture or even its operating system. ... In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed (e. ...


Characteristics

Like most imperative languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion, while a static type system prevents many unintended operations. In C, all executable code is contained within functions. Function parameters are always passed by value. Pass-by-reference is achieved in C by explicitly passing pointer values. Heterogeneous aggregate data types (struct) allow related data elements to be combined and manipulated as a unit. C program source text is free-format, using the semicolon as a statement terminator (not a delimiter). It has been suggested that ALGOL object code be merged into this article or section. ... Structured programming can be seen as a subset or subdiscipline of procedural programming, one of the major programming paradigms. ... In computer programming, scope is an enclosing context where values and expressions are associated. ... This article is about the concept of recursion. ... In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ... In computer science, a subroutine (function, method, procedure, or subprogram) is a portion of code within a larger program, which performs a specific task and can be relatively independent of the remaining code. ... In computer programming, a parameter is a variable which takes on the meaning of a corresponding argument passed in a call to a subroutine. ... In computer science, a pointer is a programming language data type whose value refers directly to (or “points to”) another value stored elsewhere in the computer memory using its address. ... A struct is the C programming languages notion of a record, a datatype that aggregates a fixed set of labelled objects, possibly of different types, into a single object. ...


C also exhibits the following more specific characteristics:

  • non-nestable function definitions, although variables may be hidden in nested blocks
  • partially weak typing; for instance, characters can be used as integers
  • low-level access to computer memory by converting machine addresses to typed pointers
  • function pointers allowing for a rudimentary form of closures and runtime polymorphism
  • array indexing as a secondary notion, defined in terms of pointer arithmetic
  • a preprocessor for macro definition, source code file inclusion, and conditional compilation
  • complex functionality such as I/O, string manipulation, and mathematical functions consistently delegated to library routines
  • around 30 reserved keywords
  • syntax divergent from ALGOL, often following the lead of C's predecessor B, for example using
    • { ... } rather than ALGOL's begin ... end
    • the equal-sign for assignment (copying), much like Fortran
    • two consecutive equal-signs to test for equality (compare to .EQ. in Fortran or the equal-sign in BASIC)
    • && and || in place of ALGOL's and and or, which
      • are syntactically distinct from the bit-wise operators & and | (used by B for both meanings)
      • never evaluate the right operand if the result can be determined from the left alone (short-circuit evaluation)
    • a large number of compound operators, such as +=, ++, etc.

In computing, weak typing, when applied to a programming language, is used to describe how the language handles datatypes. ... The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... In computer science, a pointer is a programming language data type whose value refers directly to (or “points to”) another value stored elsewhere in the computer memory using its address. ... In computer science, a closure is a function that is evaluated in an environment containing one or more bound variables. ... The Greek meaning of the words poly and morph together imply that a single entity can take on multiple forms. In the field of computer science, there are two fundamentally different types of polymorphism; subtype polymorphism, and parametric polymorphism. ... For the DNA microarray in life sciences, see DNA microarray. ... The C preprocessor (cpp) is the preprocessor for the C programming language. ... For other uses, see Macro (disambiguation) A macro in computer science is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure. ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ... Energy Input: The energy placed into a reaction. ... In computer programming and formal language theory, (and other branches of mathematics), a string is an ordered sequence of symbols. ... Illustration of an application which may use libvorbisfile. ... In computer programming, a keyword is a word or identifier that has a particular meaning to the programming language. ... It has been suggested that ALGOL object code be merged into this article or section. ... B was the name of a programming language developed at Bell Labs. ... It has been suggested that ALGOL object code be merged into this article or section. ... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ... This article is about the programming language. ... It has been suggested that ALGOL object code be merged into this article or section. ... In computer programming, a bitwise operation operates on one or two bit patterns or binary numerals at the level of their individual bits. ... B was the name of a programming language developed at Bell Labs. ... Short-circuit evaluation or minimal evaluation denotes the semantics of some boolean operators in some programming languages in which the second argument is only executed or evaluated if the first argument does not suffice to determine the value of the expression: when the first argument of and evaluates to false...

History

Early developments

The initial development of C occurred at AT&T Bell Labs between 1969 and 1973; according to Ritchie, the most creative period occurred in 1972. It was named "C" because many of its features were derived from an earlier language called "B", which according to Ken Thompson was a stripped down version of the BCPL programming language. This article is about the current AT&T. For the 1885-2005 company, see American Telephone & Telegraph. ... Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ... B was the name of a programming language developed at Bell Labs. ... Ken Thompson Kenneth Thompson (born February 4, 1943) is a pioneer of computer science notable for his contributions to the development of the C programming language and the UNIX operating system. ... BCPL (Basic Combined Programming Language) is a computer programming language that was designed by Martin Richards of the University of Cambridge in 1966; it was originally intended for use in writing compilers for other languages. ...


The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Ritchie and Thompson, incorporating several ideas from colleagues. Eventually they decided to port the operating system to a PDP-11. B's lack of functionality to take advantage of some of the PDP-11's features, notably byte addressability, led to the development of an early version of the C programming language. Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... A modified PDP-7 under restoration in Oslo, Norway The DEC PDP-7 is a minicomputer produced by Digital Equipment Corporation. ... The PDP-11 was a 16-bit minicomputer sold by Digital Equipment Corp. ... For other users of the word/name byte, see byte (disambiguation). ...


The original PDP-11 version of the Unix system was developed in assembly language. By 1973, with the addition of struct types, the C language had become powerful enough that most of the Unix kernel was rewritten in C. This was one of the first operating system kernels implemented in a language other than assembly. (Earlier instances include the Multics system (written in PL/I), and MCP (Master Control Program) for the Burroughs B5000 written in ALGOL in 1961.) Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... In computer science, the kernel is the fundamental part of an operating system. ... Multics (Multiplexed Information and Computing Service) was an extraordinarily influential early time-sharing operating system. ... PL/I (Programming Language One, pronounced pee el one) is an imperative computer programming language designed for scientific, engineering, and business applications. ... To meet Wikipedias quality standards, this article may require cleanup. ... The Burroughs large systems were the largest of three series of Burroughs Corporation mainframe computers. ... It has been suggested that ALGOL object code be merged into this article or section. ...


K&R C

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language. This book, known to C programmers as "K&R", served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as "K&R C". The second edition of the book covers the later ANSI C standard. Brian Wilson Kernighan (IPA pronunciation: , the g is silent), (born 1942 in Toronto, Ontario, Canada) is a computer scientist who worked at Bell Labs alongside Unix creators Ken Thompson and Dennis Ritchie and contributed greatly to Unix and its school of thought. ... Dennis MacAlistair Ritchie (born September 9, 1941) is an American computer scientist notable for his influence on C and other programming languages, and on operating systems such as Multics and Unix. ... The C Programming Language, second edition, by Brian Kernighan and Dennis Ritchie, widely regarded to be the authoritative reference on C. The C Programming Language (sometimes referred to as K&R or the white book) is a well-known computer science book written by Brian Kernighan and Dennis Ritchie, the... Specification may refer to several different concepts: Specification (standards) refers to specific standards Specificatio - a legal concept Specification (regression) refers to the practice of translating theory into a regression model Category: ... The C Programming Language, 2nd edition, is a widely used reference on ANSI C. ANSI C is the standard published by the American National Standards Institute (ANSI) for the C programming language. ...


K&R introduced several language features:

  • standard I/O library
  • long int data type
  • unsigned int data type
  • compound assignment operators =op were changed to op= to remove the semantic ambiguity created by the construct i=-10, which had been interpreted as i =- 10 instead of the possibly intended i = -10

Even after the publication of the 1989 C standard, for many years K&R C was still considered the "lowest common denominator" to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C code can be legal Standard C as well.


In early versions of C, only functions that returned a non-integer value needed to be declared if used before the function definition; a function used without any previous declaration was assumed to return an integer, if its value was used.


For example:

 long int SomeFunction(); /* int OtherFunction(); */ /* int */ CallingFunction() { long int test1; register /* int */ test2; test1 = SomeFunction(); if (test1 > 0) test2 = 0; else test2 = OtherFunction(); return test2; } 

All the above commented-out int declarations could be omitted in K&R C.


Since K&R function declarations did not include any information about function arguments, function parameter type checks were not performed, although some compilers would issue a warning message if a local function was called with the wrong number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Separate tools such as Unix's lint utility were developed that (among other things) could check for consistency of function use across multiple source files. On computer science, a datatype (often simply type) is a name or label for a set of values and some operations which can be performed on that set of values. ... Lint is a computer programming tool that performs the lexical and syntactic portions of the compilation with substantial additional checks, noting when variables had been used before being set, when they were used as a datatype other than that of their definition, and numerous other programming errors. ...


In the years following the publication of K&R C, several unofficial features were added to the language, supported by compilers from AT&T and some other vendors. These included:

The large number of extensions and lack of agreement on a standard library, together with the language popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization. The void type, in several programming languages derived from C, is the type for the result of a function that produces no direct result. ... A struct is the C programming languages notion of a record, a datatype that aggregates a fixed set of labelled objects, possibly of different types, into a single object. ... In computer science, a union is a data structure that stores one of several types of data at a single location. ... This article does not cite any references or sources. ... In computer programming, an enumerated type is an abstract data type used to model an attribute that has a specific number of options (or identifiers) such as the suit of a playing card (i. ... The C standard library is a now-standardised collection of header files and library routines used to implement common operations, such as input/output and string handling, in the C programming language. ...


ANSI C and ISO C

Main article: ANSI C

During the late 1970s and 1980s, versions of C were implemented for a wide variety of mainframe computers, minicomputers, and microcomputers, including the IBM PC, as its popularity began to increase significantly. The C Programming Language, 2nd edition, is a widely used reference on ANSI C. ANSI C is the standard published by the American National Standards Institute (ANSI) for the C programming language. ... For other uses, see Mainframe. ... Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). ... The Commodore 64 was one of the most popular microcomputers of its era, and is the best selling model of home computer of all time. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ...


In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. In 1989, the standard was ratified as ANSI X3.159-1989 "Programming Language C." This version of the language is often referred to as ANSI C, Standard C, or sometimes C89. The American National Standards Institute or ANSI (pronounced an-see) is a nonprofit organization that oversees the development of standards for products, services, processes and systems in the United States. ... The C Programming Language, 2nd edition, is a widely used reference on ANSI C. ANSI C is the standard published by the American National Standards Institute (ANSI) for the C programming language. ...


In 1990, the ANSI C standard (with a few minor modifications) was adopted by the International Organization for Standardization (ISO) as ISO/IEC 9899:1990. This version is sometimes called C90. Therefore, the terms "C89" and "C90" refer to essentially the same language. “ISO” redirects here. ...


One of the aims of the C standardization process was to produce a superset of K&R C, incorporating many of the unofficial features subsequently introduced. However, the standards committee also included several new features, such as function prototypes (borrowed from C++), void pointers, support for international character sets and locales, and preprocessor enhancements. The syntax for parameter declarations was also augmented to include the style used in C++, although the K&R interface continued to be permitted, for compatibility with existing source code. A is a subset of B, and B is a superset of A. In mathematics, especially in set theory, a set A is a subset of a set B, if A is contained inside B. The relationship of one set being a subset of another is called inclusion. ... A function prototype in C or C++ is a declaration of a function that omits the function body but does specify the functions name, arity, argument types and return type. ... A character encoding consists of a code that pairs a sequence of characters from a given character set (sometimes referred to as code page) with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the storage of text in computers and the... In computing, locale is a set of parameters that defines the users language, country and any special variant preferences that the user wants to see in their user interface. ...


C89 is supported by current C compilers, and most C code being written nowadays is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness. In computing, a platform describes some sort of framework, either in hardware or software, which allows software to run. ... GUI redirects here. ... In computing, endianness is the byte (and sometimes bit) ordering in memory used to represent some kind of data. ...


In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and K&R sections to take advantage of features available only in Standard C.


C99

Main article: C99

After the ANSI standardization process, the C language specification remained relatively static for some time, whereas C++ continued to evolve, largely during its own standardization effort. Normative Amendment 1 created a new standard for the C language in 1995, but only to correct some details of the C89 standard and to add more extensive support for international character sets. However, the standard underwent further revision in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999. This standard is commonly referred to as "C99." It was adopted as an ANSI standard in May 2000. The international C standard is maintained by the working group ISO/IEC JTC1/SC22/WG14. The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a low_level standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX... C++ (pronounced ) is a general-purpose programming language. ... The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a low_level standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX... Wikipedia does not have an article with this exact name. ...


C99 introduced several new features, including inline functions, several new data types (including long long int and a complex type to represent complex numbers), variable-length array, support for variadic macros (macros of variable arity) and support for one-line comments beginning with //, as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers. In computer science, an inline function is a programming language construct used to suggest to a compiler that a particular function be subjected to in-line expansion; that is, it suggests that the compiler insert the complete body of the function in every context where that function is used. ... In programming languages a data type defines a set of values and the allowable operations on those values[1]. For example, in the Java programming language, the int type represents the set of 32-bit integers ranging in value from -2,147,483,648 to 2,147,483,647, and... A complex number can be visually represented as a pair of numbers forming a vector on a diagram called an Argand diagram In mathematics, the complex numbers are the extension of the real numbers obtained by adjoining an imaginary unit, denoted i, which satisfies:[1] Every complex number can be... A variadic macro is a feature of the C Preprocessor whereby a macro may be declared to accept a varying number of arguments. ... In logic, mathematics, and computer science, the arity (synonyms include type, adicity, and rank) of a function or operation is the number of arguments or operands that the function takes. ... BCPL (Basic Combined Programming Language) is a computer programming language that was designed by Martin Richards of the University of Cambridge in 1966; it was originally intended for use in writing compilers for other languages. ...


C99 is for the most part backward compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available. GCC, Sun Studio and other C compilers now support many of the new features of C99. The GNU Compiler Collection (usually shortened to GCC) is a set of programming language compilers produced by the GNU Project. ...


As of 2007, work has begun in anticipation of another revision of the C standard, informally called "C1x". The C standards committee has adopted guidelines that should limit the adoption of new features that have not been tested by existing implementations.


Uses

C's primary use is for "system programming", including implementing operating systems and embedded system applications, due to a combination of desirable characteristics such as code portability and efficiency, ability to access specific hardware addresses, ability to "pun" types to match externally imposed data access requirements, and low runtime demand on system resources. Systems programming (or system programming) is the activity of programming system software. ... An operating system (OS) is a software that manages computer resources and provides programmers with an interface used to access those resources. ... A router, an example of an embedded system. ... In computer science, type punning is a common term for any programming technique that subverts or circumvents the type system of a programming language in order to achieve an effect that would be difficult or impossible to achieve within the bounds of the formal language. ... In computer science, runtime or run time describes the operation of a computer program, the duration of its execution, from beginning to termination (compare compile time). ...


C has also been widely used to implement end-user applications, although as applications became larger much of that development shifted to other, higher-level languages. The end user is a central concept in software engineering, referring to an abstraction of the group of persons who will ultimately use a piece of software (i. ...


One consequence of C's wide acceptance and efficiency is that the compilers, libraries, and interpreters of other higher-level languages are often implemented in C.


C is used as an intermediate language by some implementations of higher-level languages, which translate the input language to C source code, perhaps along with other object representations. The C source code is compiled by a C compiler to produce object code. This approach may be used to gain portability (C compilers exist for nearly all platforms) or for convenience (it avoids having to develop machine-specific code generators). Some programming languages which use C this way are BitC, Eiffel, Esterel, Gambit, the Glasgow Haskell Compiler, Lisp dialects, Lush, Sather, Squeak, and Vala. In computer science, an intermediate language is the language of an abstract machine designed to aid in the analysis of computer programs. ... BitC is a programming language currently being developed by researchers[1] at the Johns Hopkins University, as part of the Coyotos project. ... Eiffel is an ISO-standardized, object-oriented programming language designed to enable programmers efficiently to develop extensible, reusable, reliable software. ... Esterel is a formally defined synchronous imperative language for the programming of reactive systems. ... Gambit, also called Gambit-C, is a free software Scheme implementation, consisting of a Scheme interpreter, and a compiler which compiles Scheme to C. Its documentation [1] claims conformance to the R4RS, R5RS, and IEEE standards, as well as several SRFI. Gambit home page Categories: | | | | ... The Glasgow Haskell Compiler (or GHC) is an open source Native code Compiler for the functional programming language Haskell which was developed at the University of Glasgow. ... “LISP” redirects here. ... A dialect of a programming language is a (relatively small) variation or extension of the language that does not change its intrinsic nature. ... Lush, the Lisp Universal Shell, is an object-oriented dialect of Lisp that was initially developed as a scripting language for machine learning applications, but can also be used for general purpose, systems, and network programming or administration tasks. ... Sather is an object-oriented programming language. ... Screenshot of the Squeak VM running under X11 on Kubuntu Linux. ... Vala is a new (as of 2007) programming language, targeting GNOMEs gobject system. ...


Unfortunately, C was designed as a programming language, not as a compiler target language, and is thus less than ideal for use as an intermediate language. This has led to development of C-based intermediate languages such as C--. C-- is a name used for at least two different, unrelated programming languages, which goal is to bring the C programming language closer to computer hardware, thus creating more compact machine code while keeping C syntax, usage standards, and readability, to make use of the many programmers already familiar with...


Syntax

Main article: C syntax
See also: C variable types and declarations

Unlike languages such as FORTRAN 77, C source code is free-form which allows arbitrary use of whitespace to format code, rather than column-based or text-line-based restrictions. Comments may appear either between the delimiters /* and */, or (in C99) following // until the end of the line. The syntax of the C programming language is a set of rules that defines how a C program will be written and interpreted. ... The C programming language has an extensive system for declaring variables of different types. ... Fortran (also FORTRAN) is a statically typed, compiled, programming language originally developed in the 1950s and still heavily used for scientific computing and numerical computation half a century later. ... In computer programming, a free-form language is a programming language in which the positioning of characters on the page in program text is not significant. ...


Each source file contains declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either define new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, usually by writing the type followed by the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }) to limit the scope of declarations and to act as a single statement for control structures. For technical reasons, :) and some similar combinations starting with : redirect here. ...


As an imperative language, C uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side effect of the evaluation, functions may be called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. Structured programming is supported by if(-else) conditional execution and by do-while, while, and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. break and continue can be used to leave the innermost enclosing loop statement or skip to its reinitialization. There is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression. In computer science, a subroutine (function, procedure, or subprogram) is a sequence of code which performs a specific task, as part of a larger program, and is grouped as one, or more, statement blocks; such code is sometimes collected into software libraries. ... This article does not cite any references or sources. ... Structured programming can be seen as a subset or subdiscipline of procedural programming, one of the major programming paradigms. ...


Expressions can use a variety of built-in operators (see below) and may contain function calls. The order in which operands to most operators, as well as the arguments to functions, are evaluated is unspecified; the evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next "sequence point"; sequence points include the end of each expression statement and the entry to and return from each function call. This permits a high degree of object code optimization by the compiler, but requires C programmers to exert more care to obtain reliable results than is needed for other programming languages. A sequence point in a programming language defines any point in a computer programs execution at which it is guaranteed that all side effects of previous evaluations will have been performed, and no side effects from subsequent evaluations have yet been performed. ...


Although mimicked by many languages because of its widespread familiarity, C's syntax has often been criticized. For example, Kernighan and Ritchie say in the second edition of The C Programming Language, "C, like any other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be better."


Some specific problems worth noting are:

  • Not checking number and types of arguments when the function declaration has an empty parameter list. (This provides backward compatibility with K&R C, which lacked prototypes.)
  • Some questionable choices of operator precedence, as mentioned by Kernighan and Ritchie above, such as == binding more tightly than & and | in expressions like x & 1 == 0.
  • The use of the = operator, used in mathematics for equality, to indicate assignment, following the precedent of Fortran, PL/I, and BASIC, but unlike ALGOL and its derivatives. Ritchie made this syntax design decision consciously, based primarily on the argument that assignment occurs more often than comparison.
  • Similarity of the assignment and equality operators (= and ==), making it easy to substitute one for the other. C's weak type system permits each to be used in the context of the other without a compilation error (although some compilers produce warnings). For example, the conditional expression in if (a=b) is only true if a is not zero after the assignment.[4]
  • A lack of infix operators for complex objects, particularly for string operations, making programs which rely heavily on these operations difficult to read.
  • A declaration syntax that some find unintuitive, particularly for function pointers. (Ritchie's idea was to declare identifiers in contexts resembling their use: "declaration reflects use".)

In technology, especially computing (irrespective of platform), a product is said to be backward compatible (or upward compatible) when it is able to take the place of an older product, by interoperating with other products that were designed for the older product. ... The C Programming Language, second edition, by Brian Kernighan and Dennis Ritchie, widely regarded to be the authoritative reference on C. The C Programming Language (sometimes referred to as K&R or the white book) is a well-known computer science book written by Brian Kernighan and Dennis Ritchie, the... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ... PL/I (Programming Language One, pronounced pee el one) is an imperative computer programming language designed for scientific, engineering, and business applications. ... This article is about the programming language. ... It has been suggested that ALGOL object code be merged into this article or section. ... Infix notation is the common arithmetic and logical formula notation, in which operators are written infix-style between the operands they act on (e. ... A function pointer is a type of pointer in C, C++, D, and other C-like programming languages. ...

Operators

C supports a rich set of operators, which are symbols used within an expression to specify the manipulations to be performed while evaluating that expression. C has operators for: This is a list of operators in the C++ and C programming languages. ... Programming languages generally have a set of operators that are similar to operators in mathematics: they are somehow special functions. ... An expression in a programming language is a combination of values and functions or procedures, interpreted according to the particular rules of precedence and of association for a particular programming language, which computes and then returns another value. ...

  • arithmetic
  • equality testing
  • order relations
  • boolean logic
  • bitwise logic
  • assignment
  • increment and decrement
  • reference and dereference
  • conditional evaluation
  • member selection
  • type conversion
  • object size
  • function argument collection
  • sequencing
  • subexpression grouping

C has a fixed precedence for each operator, ensuring that statements are unambiguous.


"Hello, world" example

The "hello, world" example which appeared in the first edition of K&R has become the model for an introductory program in most programming textbooks, regardless of programming language. The program prints out "hello, world" to the standard output, which is usually a terminal or screen display. Standard output might also be a file or some other hardware device, depending on how standard output is mapped at the time the program is executed. On a modern dialect of C, a "hello, world" program would read:[5] A hello world program is a computer program that prints out Hello, world! on a display device. ... The C Programming Language, second edition, by Brian Kernighan and Dennis Ritchie, widely regarded to be the authoritative reference on C. The C Programming Language (sometimes referred to as K&R or the white book) is a well-known computer science book written by Brian Kernighan and Dennis Ritchie, the... The standard streams are a set of input and output channels featured in Unix and Unix-like operating systems, and provided by the standard I/O library (stdio. ...

 #include <stdio.h> int main(void) { printf("hello, worldn"); return 0; } 

The first line of the program is a preprocessing directive, #include. This causes the preprocessor — the first tool to examine source code as it is compiled — to substitute the line with the entire text of the stdio.h file. The header file stdio.h contains declarations for standard input and output functions such as printf. The angle brackets surrounding stdio.h indicate that stdio.h can be found using an implementation-defined search strategy. Double quotes may also be used for headers, thus allowing the implementation to supply (up to) two strategies. Typically, angle brackets are reserved for headers supplied by the C compiler, and double quotes for local or installation-specific headers. Preprocessing is the act of processing data before it is parsed. ...


The next line indicates that a function named main is being defined. The main function serves a special purpose in C programs: The run-time environment calls the main function to begin program execution. The type specifier int indicates that the return value, the value of evaluating the main function that is returned to its invoker (in this case the run-time environment), is an integer. The keyword void as a parameter list indicates that the main function takes no arguments.[6] In some programming languages, the main function is where a program starts execution. ...


The opening curly brace indicates the beginning of the definition of the main function.


The next line calls (executes the code for) a function named printf, which is declared in the included header stdio.h and supplied from a system library. In this call, the printf function is passed (provided with) a single argument, the address of the first character in the string literal "hello, worldn". The string literal is an unnamed array with elements of type char, set up automatically by the compiler with a final 0-valued character to mark the end of the array (printf needs to know this). The n is an escape sequence that C translates to the newline character, which on output signifies the end of the current line. The return value of the printf function is of type int, but it is silently discarded since it is not used by the caller. (A more careful program might test the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement. Several programming languages implement a printf function, to output a formatted string. ... Illustration of an application which may use libvorbisfile. ... For the DNA microarray in life sciences, see DNA microarray. ... In computing, a newline is a special character or sequence of characters signifying the end of a line of text. ...


The return line terminates the execution of the main function and causes it to return the integer value 0, which is interpreted by the run-time system as an exit code (indicating successful execution).


The closing curly brace indicates the end of the code for the main function.


Data structures

C has a static weak typing type system that shares some similarities with that of other ALGOL descendants such as Pascal. There are built-in types for integers of various sizes, both signed and unsigned, floating-point numbers, characters, and enumerated types (enum). C99 added a boolean datatype. There are also derived types including arrays, pointers, records (struct), and untagged unions (union). In computing, weak typing, when applied to a programming language, is used to describe how the language handles datatypes. ... In computer science, a type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. ... It has been suggested that ALGOL object code be merged into this article or section. ... Pascal is a structured imperative computer programming language, developed in 1970 by Niklaus Wirth as a language particularly suitable for structured programming. ... A floating-point number is a digital representation for a number in a certain subset of the rational numbers, and is often used to approximate an arbitrary real number on a computer. ... In computer science, the Boolean datatype, sometimes called the logical datatype, is a primitive datatype having one of two values: non-zero (often 1, or -1) and zero (which are equivalent to true and false, respectively). ... For the DNA microarray in life sciences, see DNA microarray. ... It has been suggested that Software pointer be merged into this article or section. ... This article is about the data structure. ... In computer science, a union is a data structure that stores one of several types of data at a single location. ...


C is often used in low-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure type correctness of most expressions, but the programmer can override the checks in various ways, either by using a type cast to explicitly convert a value from one type to another, or by using pointers or unions to reinterpret the underlying bits of a value in some other way. In computer science, type conversion or typecasting refers to changing an entity of one data type into another. ...


Pointers

C supports the use of pointers, a very simple type of reference that records, in effect, the address or location of an object or function in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment and also pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-within-word field), but since a pointer's type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile time. Pointer arithmetic is automatically scaled by the size of the pointed-to data type. (See Array-pointer interchangeability below.) Pointers are used for many different purposes in C. Text strings are commonly manipulated using pointers into arrays of characters. Dynamic memory allocation, which is described below, is performed using pointers. Many data types, such as trees, are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for callbacks from event handlers. This article is about a general notion of reference in computing. ... Pointer arithmetic is a particular arithmetic involving pointers, typical of the C programming language. ... In computer programming and formal language theory, (and other branches of mathematics), a string is an ordered sequence of symbols. ... In computer science, dynamic memory allocation is the allocation of memory storage for use in a computer program during the runtime of that program. ... A simple example unordered tree In computer science, a tree is a widely-used data structure that emulates a tree structure with a set of linked nodes. ... For a discussion of callback with computer modems, see callback (telecommunications). ...


A null pointer is a pointer value that points to no valid location (it is often represented by address zero). Dereferencing a null pointer is therefore meaningless, typically resulting in a run-time error. Null pointers are useful for indicating special cases such as no next pointer in the final node of a linked list, or as an error indication from functions returning pointers. In the C Programming Language, a null pointer is a special pointer which is guaranteed to compare unequal to a pointer to any object or function. ... In computer science, a linked list is one of the fundamental data structures, and can be used to implement other data structures. ...


Void pointers (void *) point to objects of unknown type, and can therefore be used as "generic" data pointers. Since the size and type of the pointed-to object is not known, void pointers cannot be dereferenced, nor is pointer arithmetic on them allowed, although they can easily be (and in many contexts implicitly are) converted to and from any other object pointer type.


Pointers are a primary source of potential danger. Because they are typically unchecked, a pointer can be made to point to any arbitrary location, causing undesirable effects. Although properly-used pointers point to safe places, they can be moved to unsafe places using invalid pointer arithmetic; the memory they point to may be deallocated and reused (dangling pointers); they may be uninitialized (wild pointers); or they may be directly assigned a value using a cast, union, or through another corrupt pointer. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Other languages address these problems by using more restrictive reference types. In computer science, a pointer is a programming language datatype whose value refers directly to (points to) another value stored elsewhere in the computer memory using its address. ... Dangling pointers in programming are pointers whose objects have since been deleted or deallocated, without modifying the value of the pointer. ... Wild pointers are pointers that have not been initialized (set to point to a valid address) and can make a program crash and/or behave weird. ... This article is about a general notion of reference in computing. ...


Arrays

Array types in C are always one-dimensional and, traditionally, of a fixed, static size specified at compile time. (The more recent C99 standard also allows a form of variable-length arrays.) However, it is also possible to allocate a block of memory (of arbitrary size) at run-time, using the standard library's malloc function, and treat it as an array. C's unification of arrays and pointers (see below) means that true arrays and these dynamically-allocated, simulated arrays are virtually interchangeable. Since arrays are always accessed (in effect) via pointers, array accesses are typically not checked against the underlying array size, although the compiler may provide bounds checking as an option. Array bounds violations are therefore possible and rather common in carelessly written code, and can lead to various repercussions, including illegal memory accesses, corruption of data, buffer overrun and run-time exceptions. For the DNA microarray in life sciences, see DNA microarray. ...


C does not have a special provision for declaring multidimensional arrays, but rather relies on recursion within the type system to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multidimensional array" can be thought of as increasing in row-major order. Row-major order describes a way to store a multidimensional array in linear memory. ...


Although C supports static arrays, it is not required that array indices be validated (bounds checking). For example, one can try to write to the sixth element of an array with five elements, yielding generally undesirable results. This type of bug, called a buffer overflow, has been notorious as the source of a number of security problems. On the other hand, since bounds checking elimination technology was largely nonexistent when C was defined, bounds checking came with a severe performance penalty, particularly in numerical computation. A few years earlier, some Fortran compilers had a switch to toggle bounds checking on or off; however, this would have been much less useful for C, where array arguments are passed as simple pointers. In computer programming, bounds checking is the name given to any method of detecting whether or not an index given lies within the limits of an array. ... [[Media:Media:Example. ... Array Bound Checks Removal is a compiler optimization, which tries to remove bounds checking in places where it is known at compile-time that the index stays within the limits of an array. ... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ...


Multidimensional arrays are commonly used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C array is particularly well suited to this particular task. However, since arrays are passed merely as pointers, the bounds of the array must be known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this is to allocate the array with an additional "row vector" of pointers to the columns.) These issues are discussed in the book Numerical Recipes in C, chapter 1.2, page 20ff.[7] Linear algebra is the branch of mathematics concerned with the study of vectors, vector spaces (also called linear spaces), linear maps (also called linear transformations), and systems of linear equations. ... Numerical Recipes is the generic title of an influential series of books on algorithms and numerical analysis, all by William Press, Saul Teukolsky, William Vetterling and Brian Flannery: // Numerical Recipes in Fortran: The Art of Scientific Computing by William Press, Saul Teukolsky, William Vetterling and Brian Flannery The books contain...


C99 introduced "variable-length arrays" which address some, but not all, of the issues with ordinary C arrays.

See also: C string

In computing, C strings are character sequences stored as one-dimensional character arrays and terminated with a null character (0). The name refers to the ubiquitous C programming language using this string representation, and is used elsewhere to distinguish this often-used representation from others. ...

Array-pointer interchangeability

A distinctive (but potentially confusing) feature of C is its treatment of arrays and pointers. The array-subscript notation x[i] can also be used when x is a pointer; the interpretation (using pointer arithmetic) is to access the (i+1)th of several adjacent data objects pointed to by x, counting the object that x points to (which is x[0]) as the first element of the array.


Formally, x[i] is equivalent to *(x + i). Since the type of the pointer involved is known to the compiler at compile time, the address that x + i points to is not the address pointed to by x incremented by i bytes, but rather incremented by i multiplied by the size of an element that x points to. The size of these elements can be determined with the operator sizeof by applying it to any dereferenced element of x, as in n = sizeof *x or n = sizeof x[0]. In C programming language and C++, an unary operator sizeof is used to calculate size of various datatypes. ...


Furthermore, in most expression contexts (a notable exception is sizeof array), the name of an array is automatically converted to a pointer to the array's first element; this implies that an array is never copied as a whole when named as an argument to a function, but rather only the address of its first element is passed. Therefore, although C's function calls use pass-by-value semantics, arrays are in effect passed by reference. Parameters are a way of allowing the same sequence of commands to operate on different data without re-specifying the instructions. ... This article is about a general notion of reference in computing. ...


The number of elements in a declared array a can be determined as sizeof a / sizeof a[0].


An interesting demonstration of the interchangeability of pointers and arrays is shown below. The four assignments are equivalent and each is valid C code. Note how the last line contains the strange code i[x] = 1;, which has the index variable i apparently interchanged with the array variable x. This last line might be found in obfuscated C code. The International Obfuscated C Code Contest (abbr. ...

 /* x designates an array */ x[i] = 1; *(x + i) = 1; *(i + x) = 1; i[x] = 1; /* strange, but correct: i[x] is equivalent to *(i + x) */ 

However, there is a distinction to be made between arrays and pointer variables. Even though the name of an array is in most expression contexts converted to a pointer (to its first element), this pointer does not itself occupy any storage. Consequently, you cannot change what an array "points to", and it is impossible to assign to an array. (Arrays may however be copied using the memcpy function, for example.)


Memory management

One of the most important functions of a programming language is to provide facilities for managing memory and the objects that are stored in memory. C provides three distinct ways to allocate memory for objects: The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ...

  • Static memory allocation: space for the object is provided in the binary at compile-time; these objects have an extent (or lifetime) as long as the binary which contains them is loaded into memory
  • Automatic memory allocation: temporary objects can be stored on the stack, and this space is automatically freed and reusable after the block in which they are declared is exited
  • Dynamic memory allocation: blocks of memory of arbitrary size can be requested at run-time using library functions such as malloc from a region of memory called the heap; these blocks persist until subsequently freed for reuse by calling the library function free

These three approaches are appropriate in different situations and have various tradeoffs. For example, static memory allocation has no allocation overhead, automatic allocation may involve a small amount of overhead, and dynamic memory allocation can potentially have a great deal of overhead for both allocation and deallocation. On the other hand, stack space is typically much more limited and transient than either static memory or heap space, and dynamic memory allocation allows allocation of objects whose size is known only at run-time. Most C programs make extensive use of all three. Static memory allocation refers to the process of allocating memory at compile-time before the associated program is executed, unlike dynamic memory allocation or automatic memory allocation where memory is allocated as required at run-time. ... In computer science and mathematics, a variable (pronounced ) (sometimes called an object or identifier in computer science) is a symbolic representation used to denote a quantity or expression. ... It has been suggested that this article or section be merged with Function stack. ... In computer science, a call stack is a special stack which stores information about the active subroutines of a computer program. ... In computer science, dynamic memory allocation is the allocation of memory storage for use in a computer program during the runtime of that program. ... In computing, malloc is a subroutine provided in the C programming languages and C++ programming languages standard library for performing dynamic memory allocation. ... In computer science, dynamic memory allocation is the allocation of memory storage for use in a computer program during the runtime of that program. ... In computing, malloc is a subroutine provided in the C programming languages and C++ programming languages standard library for performing dynamic memory allocation. ...


Where possible, automatic or static allocation is usually preferred because the storage is managed by the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. However, many data structures can grow in size at runtime, and since static allocations (and automatic allocations in C89 and C90) must have a fixed size at compile-time, there are many situations in which dynamic allocation must be used. Prior to the C99 standard, variable-sized arrays were a common example of this (see "malloc" for an example of dynamically allocated arrays). In computing, malloc is a subroutine provided in the C programming languages and C++ programming languages standard library for performing dynamic memory allocation. ...


Automatically and dynamically allocated objects are not necessarily initialized; they initially have indeterminate values (typically, whatever bit pattern happens to be present in the storage, which might not even represent a valid value for that type). If the program attempts to use such an uninitialized value, the results are undefined. Many modern compilers try to detect and warn about this problem, but both false positives and false negatives occur. This article is about the unit of information. ... This article does not cite any references or sources. ... Type I errors (or α error, or false positive) and type II errors (β error, or a false negative) are two terms used to describe statistical errors. ...


Another common problem is that heap memory has to be manually synchronized with its actual usage in any program for it to be reused as much as possible. For example, if the only pointer to a memory allocation goes out of scope or has its value overwritten before free() has been called, then that memory cannot be recovered for later reuse and is essentially lost to the program, a phenomenon known as a memory leak. Conversely, it is possible to release memory too soon and continue to access it; however, since the allocation system can re-allocate or itself use the freed memory, unpredictable behavior is likely to occur when the multiple users corrupt each other's data. Typically, the symptoms will appear in a portion of the program far removed from the actual error. Such issues are ameliorated in languages with automatic garbage collection or RAII. In computing, malloc is a subroutine provided in the C programming languages and C++ programming languages standard library for performing dynamic memory allocation. ... In computer science, a memory leak is a particular kind of unintentional memory consumption by a computer program where the program fails to release memory when no longer needed. ... In computer science, garbage collection (GC) is a form of automatic memory management. ... Resource Acquisition Is Initialization, often referred to by the acronym RAII, is a popular design pattern in C++ and D. The technique combines acquisition and release of resources with initialization and uninitialization of objects. ...


Libraries

The C programming language uses libraries as its primary method of extension. In C, a library is a set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a program, and declarations of special data types and macro symbols used with these functions. In order for a program to use a library, it must include the library's header file, and the library must be linked with the program, which in many cases requires compiler flags (e.g., -lm, shorthand for "math library"). In computer science, a library is a collection of subprograms used to develop software. ... In computer programming, especially in the C programming language or C++, a header file is a text file containing small bits of program code, which is used to describe the contents of the main body of code to other modules. ... In computer command line interfaces, a command-line argument is an argument sent to a program being called. ...


The most common C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation. ("Freestanding" [embedded] C implementations may provide only a subset of the standard library.) This library supports stream input and output, memory allocation, mathematics, character strings, and time values. The C standard library is a now-standardised collection of header files and library routines used to implement common operations, such as input/output and string handling, in the C programming language. ... This is an incomplete list of ISO standards. ... ANSI C (Standard C) is a variant of the C programming language. ...


Another common set of C library functions are those used by applications specifically targeted for Unix and Unix-like systems, especially functions which provide an interface to the kernel. These functions are detailed in various standards such as POSIX and the Single UNIX Specification. Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... Diagram of the relationships between several Unix-like systems A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ... A kernel connects the application software to the hardware of a computer. ... POSIX or Portable Operating System Interface[1] is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API) for software compatible with variants of the Unix operating system. ... The Single UNIX Specification (SUS) is the collective name of a family of standards for computer operating systems to qualify for the name Unix. The SUS is developed and maintained by the Austin Group, based on earlier work by the IEEE and The Open Group. ...


Since many programs have been written in C, there are a wide variety of other libraries available. Libraries are often written in C because C compilers generate efficient object code; programmers then create interfaces to the library so that the routines can be used from higher-level languages like Java, Perl, and Python. In computer science, object file or object code is an intermediate representation of code generated by a compiler after it processes a source code file. ... Java language redirects here. ... For other uses, see Perl (disambiguation). ... Python is a general-purpose, high-level programming language. ...


Minimalism

A popular saying, repeated by such notable language designers as Bjarne Stroustrup, is that "C makes it easy to shoot yourself in the foot."[8] In other words, C permits some operations that are sometimes not desirable, and thus many simple programming errors are not detected by the compiler and may not be readily apparent at runtime. If sufficient care and discipline are not used in programming and maintenance, this may lead to programs with unpredictable behavior and security holes. (Although this is not unique to C, C provides less protection than do many other programming languages.) Bjarne Stroustrup Bjarne Stroustrup (IPA: ) (born December 30, 1950 in Aarhus, Denmark) is a computer scientist and the College of Engineering Chair Professor of Computer Science at Texas A&M University. ...


The designers wanted to avoid compile- and run-time checks that were too expensive when C was first implemented. With time, external tools were developed to perform some of these checks. Nothing prevents an implementation from providing such checks, but nothing requires it, either. In computer science, runtime or run time describes the operation of a computer program, the duration of its execution, from beginning to termination (compare compile time). ...


In their response to criticism of C not being a strongly-typed programming language, Kernighan and Ritchie made reference to the basic design philosophy of C: "Nevertheless, C retains the basic philosophy that programmers know what they are doing; it only requires that they state their intentions explicitly."[9][10] In computer science and computer programming, the term strong typing is used to describe those situations where programming languages specify one or more restrictions on how operations involving values having different datatypes can be intermixed. ... A design philosophy is a guide to help make choices when designing. ...


Absent features

The relatively low-level nature of the language affords the programmer close control over what the computer does, while allowing specially tailoring and aggressive optimization for a particular platform. This allows the code to run efficiently on very limited hardware, such as embedded systems. What is an Embedded System? Electronic devices that incorporate a computer(usually a microprocessor) within their implementation. ...


C does not have some features that are available in some other programming languages:

A number of these features are available as extensions in some compilers, or can be supplied by third-party libraries, or can be simulated by adopting certain coding disciplines. In computer science, garbage collection (GC) is a form of automatic memory management. ... In computer programming, bounds checking is the name given to any method of detecting whether or not an index given lies within the limits of an array. ... Array programming languages (also known as vector or multidimensional languages) generalize operations on scalars to apply transparently to vectors, matrices, and higher dimensional arrays. ... In computer science, the term range may refer to one of two things: The maximum and minimum values that may be stored in a variable. ... For use in mathematics, see Boolean algebra (structure). ... A nested function is a function which can only be called from its parent function. ... In computer science, a closure is a function that is evaluated in an environment containing one or more bound variables. ... In computer science, a generator is a special routine that can be used to control the iteration behaviour of a loop. ... In computer science, coroutines are program components that generalize subroutines to allow multiple entry points and suspending and resuming of execution at certain locations. ... Setjmp and longjmp are functions used in C programming language for non-local exits or exception handling. ... setcontext is one of a family of C library functions (the others being getcontext, makecontext and swapcontext) used for context control. ... Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of some condition that changes the normal flow of execution. ... In computer programming, error codes are enumerated messages that correspond to faults in a specific software application. ... In computer science, a subroutine (function, procedure, or subprogram) is a sequence of code which performs a specific task, as part of a larger program, and is grouped as one, or more, statement blocks; such code is sometimes collected into software libraries. ... In mathematics, an operator is a function that performs some sort of operation on a number, variable, or function. ... Method overloading is a feature found in various programming languages such as C++ and Java that allows the creation of several functions with the same name which differ from each other in terms of the type of the inbananaput and the type of the output of the function. ... Generic programming is a style of computer programming where algorithms are written in an extended grammar and are made adaptable by specifying variable parts that are then somehow instantiated later by the compiler with respect to the base grammar. ... Object-oriented programming (OOP) is a programming paradigm that uses objects and their interactions to design applications and computer programs. ... In simple terms, polymorphism lets you treat derived class members just like their parent class members. ... This article or section does not cite any references or sources. ... In computer science, the principle of information hiding is the hiding of design decisions in a computer program that are most likely to change, thus protecting other parts of the program from change if the design decision is changed. ... Many programming languages, operating systems, and other software development environments support what are called threads of execution. ... A computer network is a system for communication among two or more computers. ... This article is about the scientific discipline of computer graphics. ...


Undefined behaviour

Many operations in C that have undefined behavior are not required to be diagnosed at compile time. In the case of C, "undefined behavior" means that the exact behavior which arises is not specified by the standard, and exactly what will happen does not have to be documented by the C implementation. A famous, although misleading, expression in the newsgroups comp.std.c and comp.lang.c is that the program could cause "demons to fly out of your nose".[12] Sometimes in practice what happens for an instance of undefined behavior is a bug that is hard to track down and which may corrupt the contents of memory. Sometimes a particular compiler generates well-behaved actions that are not the same as would be obtained using a different C compiler. The reason some behavior has been left undefined is to allow the compiler to generate more efficient executable code for well-defined behavior, which was deemed important for C's primary role as a systems implementation language; it is the programmer's responsibility to avoid undefined behavior. Examples of undefined behavior are: In computer science, undefined behavior is a feature of some programming languages — most famously C. In these languages, to simplify the specification and allow some flexibility in implementation, the specification leaves the results of certain operations specifically undefined. ... In computer science, compile time, as opposed to runtime, is the time when a compiler compiles code written in a programming language into an executable form. ... A newsgroup is a repository usually within the Usenet system, for messages posted from many users at different locations. ... A software bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from behaving as intended (e. ...

  • accessing outside the bounds of an array
  • overflowing a signed integer
  • reaching the end of a function without finding a return statement, when the return value is used
  • reading the value of a variable before initializing it

These operations are all programming errors that could occur using many programming languages; C draws criticism because its standard explicitly identifies numerous cases of undefined behavior, including some where the behavior could have been made well defined, and does not specify any run-time error handling mechanism.


Invoking fflush() on a stream opened for input is an example of a different kind of undefined behavior, not necessarily a programming error but a case for which some conforming implementations may provide well-defined, useful semantics (in this example, presumably discarding input through the next new-line) as an allowed extension. fflush is a C function belonging to the ANSI C standard library, and included in the file stdio. ...


Language tools

Tools have been created to help C programmers avoid some of the problems inherent in the language.


Automated source code checking and auditing are beneficial in any language, and for C many such tools exist, such as Lint. A common practice is to use Lint to detect questionable code when a program is first written. Once a program passes Lint, it is then compiled using the C compiler. Also, many compilers can optionally warn about syntactically valid constructs that are likely to actually be errors. Lint is a computer programming tool that performs the lexical and syntactic portions of the compilation with substantial additional checks, noting when variables had been used before being set, when they were used as a datatype other than that of their definition, and numerous other programming errors. ...


There are also compilers, libraries and operating system level mechanisms for performing array bounds checking, buffer overflow detection, serialization and automatic garbage collection, that are not a standard part of C. [[Media:Media:Example. ... This article is about data structure encoding. ... In computer science, garbage collection (GC) is a form of automatic memory management. ...


Cproto is a program that will read a C source file and output prototypes of all the functions within the source file. This program can be used in conjunction with the make command to create new files containing prototypes each time the source file has been changed. These prototype files can be included by the original source file (e.g., as "filename.p"), which reduces the problems of keeping function definitions and source files in agreement. In computer programming, make is a utility for automatically building large applications. ...


Related languages

When object-oriented languages became popular, C++ and Objective-C were two different extensions of C that provided object-oriented capabilities. Both languages were originally implemented as preprocessors -- source code was translated into C, and then compiled with a C compiler. C++ (pronounced ) is a general-purpose programming language. ... Objective-C, often referred to as ObjC or more seldomly as Objective C or Obj-C, is an object oriented programming language implemented as an extension to C. It is used primarily on Mac OS X and GNUstep, two environments based on the OpenStep standard, and is the primary language...


Bjarne Stroustrup devised the C++ programming language as one approach to providing object-oriented functionality with C-like syntax. C++ adds greater typing strength, scoping and other tools useful in object-oriented programming and permits generic programming via templates. Nearly a superset of C, C++ now supports most of C, with a few exceptions (see Compatibility of C and C++ for an exhaustive list of differences). Bjarne Stroustrup Bjarne Stroustrup (IPA: ) (born December 30, 1950 in Aarhus, Denmark) is a computer scientist and the College of Engineering Chair Professor of Computer Science at Texas A&M University. ... Generic programming is a style of computer programming where algorithms are written in an extended grammar and are made adaptable by specifying variable parts that are then somehow instantiated later by the compiler with respect to the base grammar. ... The C and C++ programming languages are closely related, as C++ grew out of C and is many ways a superset of the latter. ...


Unlike C++, which maintains nearly complete backwards compatibility with C, the D language makes a clean break with C while maintaining the same general syntax. It abandons a number of features of C which Walter Bright (the designer of D) considered undesirable, including the C preprocessor and trigraphs. Some, but not all, of D's extensions to C overlap with those of C++. For other programming languages named D, see D (disambiguation)#Computing. ... Walter Bright is a computer programmer known for the design of the D programming language. ... The C preprocessor (cpp) is the preprocessor for the C programming language. ... In the C family of programming languages, a trigraph is a sequence of three characters, the first two of which are both question marks, that represents a single character. ...


Objective-C was originally a very "thin" layer on top of, and remains a strict superset of, C that permits object-oriented programming using a hybrid dynamic/static typing paradigm. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations and function calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk. Objective-C, often referred to as ObjC or more seldomly as Objective C or Obj-C, is an object oriented programming language implemented as an extension to C. It is used primarily on Mac OS X and GNUstep, two environments based on the OpenStep standard, and is the primary language... For other uses, see Small talk. ...


C has also directly or indirectly influenced many later languages such as Java, C#, Perl, PHP, JavaScript, LPC, and Unix's C Shell. The most pervasive influence has been syntactical: all of the languages mentioned combine the statement and (more or less recognizably) expression syntax of C with type systems, data models and/or large-scale program structures that differ from those of C, sometimes radically. Java language redirects here. ... C# (see section on name, pronunciation) is an object-oriented programming language developed by Microsoft as part of the . ... For other uses, see Perl (disambiguation). ... For other uses, see PHP (disambiguation). ... JavaScript is a scripting language most often used for client-side web development. ... The LPC programming language is an object-oriented programming language derived from C and developed by Lars Pensjö to facilitate MUD building on LPMuds. ... The C shell (csh) is a Unix shell developed by Bill Joy for the BSD Unix system. ...


See also

Programming languages are used for controlling the behavior of a machine (often a computer). ... Impulse C is a subset of the C language combined with a C-compatible function library supporting parallel programming, in particular for programming of applications targeting FPGA devices. ... The International Obfuscated C Code Contest (abbr. ... This is a list of articles which contain programming examples with source code written in the programming language C: C syntax Callback Comment ctype. ... This page is dedicated to list all current compilers, compiler generators, interpreters, translators, etc. ... The computer programming languages C and Pascal are often compared[1] to each other, sometimes heatedly, probably because the languages have similar times of origin, influences, and purposes, and so represent two philosophical approaches to a similar need. ...

Footnotes

  1. ^ Dennis M. Ritchie (Jan 1993). The Development of the C Language. Retrieved on Jan 1, 2008. “The scheme of type composition adopted by C owes considerable debt to Algol 68, although it did not, perhaps, emerge in a form that Algol's adherents would approve of.”
  2. ^ Stewart, Bill (2000-01-07). History of the C Programming Language. Living Internet. Retrieved on 2006-10-31.
  3. ^ Patricia K. Lawlis, c.j. kemp systems, inc. (1997). Guidelines for Choosing a Computer Language: Support for the Visionary Organization. Ada Information Clearinghouse. Retrieved on 2006-07-18.
  4. ^ http://www.cs.ucr.edu/~nxiao/cs10/errors.htm 10 Common Programming Mistakes in C
  5. ^ The original example code will compile on most modern compilers that are not in compliance mode, but does not meet the requirements of either C89 or C99. Compiling the program given in the book in C99 compliance mode will result in warning or error messages. For C89, a diagnostic message is not required, but often one will be issued anyway.
  6. ^ The main function actually has two arguments, int argc and char *argv[], respectively, which can be used to handle command line arguments. The C standard requires that both forms of main be supported, which is special treatment not afforded any other function.
  7. ^ http://www.nrbook.com/a/bookcpdf/c1-2.pdf
  8. ^ http://www.research.att.com/~bs/bs_faq.html#really-say-that Stroustrup: FAQ
  9. ^ Dennis Ritchie. The Development of the C Language. Retrieved on 2006-07-26.
  10. ^ Brian W. Kernighan and Dennis M. Ritchie: The C Programming Language, 2nd ed., Prentice Hall, 1988, p. 3.
  11. ^ The 1999 revision of the C standard added a type _Bool, but it was not retrofit into the language's existing Boolean contexts.
  12. ^ Jargon File entry for nasal demons.

Year 2000 (MM) was a leap year starting on Saturday. ... is the 7th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 304th day of the year (305th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 199th day of the year (200th in leap years) in the Gregorian calendar. ... In computer command line interfaces, a command-line argument is an argument sent to a program being called. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... Pearson can mean Pearson PLC the media conglomerate. ...

References

  • Brian Kernighan, Dennis Ritchie: The C Programming Language. Also known as K&R — The original book on C.
    • 1st, Prentice Hall 1978; ISBN 0-13-110163-3. Pre-ANSI C.
    • 2nd, Prentice Hall 1988; ISBN 0-13-110362-8. ANSI C.
  • ISO/IEC 9899. Official C99 documents, including technical corrigenda and a rationale. As of 2007 the latest version of the standard is ISO/IEC 9899:TC3PDF (3.61 MiB).
  • Samuel P. Harbison, Guy L. Steele: C: A Reference Manual. This book is excellent as a definitive reference manual, and for those working on C compilers. The book contains a BNF grammar for C.
    • 5th, Prentice Hall 2002; ISBN 0-13-089592-X.
  • Derek M. Jones: The New C Standard: A Cultural and Economic Commentary, Addison-Wesley, ISBN 0-201-70917-1, online material
  • Robert Sedgewick: Algorithms in C, Addison-Wesley, ISBN 0-201-31452-5 (Part 1–4) and ISBN 0-201-31663-3 (Part 5)
  • William H. Press, Saul A. Teukolsky, William T. Vetterling, Brian P. Flannery: Numerical Recipes in C (The Art of Scientific Computing), ISBN 0-521-43108-5

Brian Wilson Kernighan (IPA pronunciation: , the g is silent), (born 1942 in Toronto, Ontario, Canada) is a computer scientist who worked at Bell Labs alongside Unix creators Ken Thompson and Dennis Ritchie and contributed greatly to Unix and its school of thought. ... Dennis MacAlistair Ritchie (born September 9, 1941) is an American computer scientist notable for his influence on C and other programming languages, and on operating systems such as Multics and Unix. ... The C Programming Language, second edition, by Brian Kernighan and Dennis Ritchie, widely regarded to be the authoritative reference on C. The C Programming Language (sometimes referred to as K&R or the white book) is a well-known computer science book written by Brian Kernighan and Dennis Ritchie, the... “PDF” redirects here. ... MiB redirects here. ... Guy Lewis Steele, Jr. ... This article is about the computing term. ... The Backus-Naur form (BNF) (also known as Backus normal form) is a metasyntax used to express context-free grammars: that is, a formal way to describe formal languages. ... For other men with the same name, see Robert Sedgewick Robert Sedgewick is the author of the celebrated book series Algorithms, published by Addison-Wesley. ... Numerical Recipes is the generic title of an influential series of books on algorithms and numerical analysis, all by William Press, Saul Teukolsky, William Vetterling and Brian Flannery: // Numerical Recipes in Fortran: The Art of Scientific Computing by William Press, Saul Teukolsky, William Vetterling and Brian Flannery The books contain...

External links

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Image File history File links Wikibooks-logo-en. ... Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is a wiki for the creation of books. ... Image File history File links This is a lossless scalable vector image. ... Wikiversity logo Wikiversity is a Wikimedia Foundation beta project[1], devoted to learning materials and activities, located at www. ... “PDF” redirects here. ... MiB redirects here. ... Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (September 9, 1941- ) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and UNIX. Born in Bronxville, New York, Ritchie graduated from Harvard with degrees in physics and applied mathematics. ... developerWorks is resource by IBM for software developers. ... The University of Strathclyde (Scottish Gaelic: ) is a university in Glasgow, Scotland. ... The Creative Commons (CC) is a non-profit organization devoted to expanding the range of creative work available for others legally to build upon and share. ... Lysator is the Academic Computer Club at the Linköping University, Sweden. ... “PDF” redirects here. ... MiB redirects here. ... The C standard library is a now-standardised collection of header files and library routines used to implement common operations, such as input/output and string handling, in the C programming language. ... Glibc is the GNU projects C standard library. ... The dietlibc is a C library, similar to Glibc. ... uClibc is a small C standard library intended for embedded Linux systems. ... Newlib is a C library intended for use on embedded systems. ... The programming language C is widely used, minimalistic and low-level by design. ... In computing, C strings are character sequences stored as one-dimensional character arrays and terminated with a null character (0). The name refers to the ubiquitous C programming language using this string representation, and is used elsewhere to distinguish this often-used representation from others. ... The syntax of the C programming language is a set of rules that defines how a C program will be written and interpreted. ... The C preprocessor (cpp) is the preprocessor for the C programming language. ... The C programming language has an extensive system for declaring variables of different types. ... This page aims to alphabetically list all the predefined functions used in the C standard library, and a few of the non-standard functions. ... C++ (pronounced ) is a general-purpose programming language. ... Objective-C, often referred to as ObjC or more seldomly as Objective C or Obj-C, is an object oriented programming language implemented as an extension to C. It is used primarily on Mac OS X and GNUstep, two environments based on the OpenStep standard, and is the primary language... For other programming languages named D, see D (disambiguation)#Computing. ... C# (see section on name, pronunciation) is an object-oriented programming language developed by Microsoft as part of the . ... The C and C++ programming languages are closely related, as C++ grew out of C and is many ways a superset of the latter. ... This is a list of operators in the C++ and C programming languages. ... The computer programming languages C and Pascal are often compared[1] to each other, sometimes heatedly, probably because the languages have similar times of origin, influences, and purposes, and so represent two philosophical approaches to a similar need. ... A C to Java byte-code compiler is a compiler that translates C code to Java byte-code so that it can be run on a Java Virtual Machine. ...

  Results from FactBites:
 
Introduction to C, by The Linux Information Project (LINFO) (1491 words)
C is in many ways the most important of the hundreds of programming languages that have been developed in the world to date.
C remains particularly popular in the world of Unix-like operating systems, and, for example, most of the Linux kernel (i.e., the core of the operating system) is written in C. Moreover, it is one of the most frequently studied languages in computer science classes.
C differs significantly from assembly languages in that it is much easier to read and write programs in it, particularly lengthy ones, because its syntax and vocabulary are much closer to those of the English language.
Information about C programming language (5947 words)
C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system.
C's primary use is for "system programming", including implementing operating systems and embedded system applications, due to a combination of desirable characteristics such as code portability and efficiency, ability to access specific hardware addresses, ability to "pun" types to match externally imposed data access requirements, and low runtime demand on system resources.
One consequence of C's wide acceptance and efficiency is that the compilers, libraries, and interpreters of other higher-level languages are often implemented in C. C is used as an intermediate language by some higher-level languages.
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