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Encyclopedia > C Programming Language
C

The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language.
Paradigm: imperative (procedural) systems implementation language
Appeared in: 1972
Designed by: Dennis Ritchie
Developer: Dennis Ritchie & Bell Labs
Typing discipline: static, weak
Major implementations: GCC, MSVC, Borland C, Watcom C
Dialects: ObjC, C++
Influenced by: B (BCPL,CPL), Algol68, Assembly, Pascal
Influenced: awk, csh, C++, ObjC, Concurrent C, Java, Javascript, etc.
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The C programming language (often, just "C") is a general-purpose, procedural, imperative computer programming language developed in the early 1970s by Dennis Ritchie for use on the Unix operating system. It has since spread to many other operating systems, and is now one of the most widely used programming languages. C also has had a great influence on many other popular languages,[1] especially C++ which was originally designed as an enhancement to C. It is the most commonly used programming language for writing system software,[2][3] though it is also widely used for writing applications. Though not originally designed as a language for teaching, and despite its somewhat unforgiving character, C is commonly used in computer science education, in part because the language is so pervasive. Download high resolution version (976x1364, 172 KB)Cover of Kernighan & Ritchie book on C Source: [1] This work is copyrighted. ... The C Programming Language, by Brian Kernighan and Dennis Ritchie; one of the most read and trusted books on C. The C Programming Language, 1st edition, also known as the Old Testament. The C Programming Language (also known as K&R or the white book) is a famous computer science... Brian Wilson Kernighan (pronounced Ker-ni-han; the g is silent; born 1942) is a computer scientist who worked at the Bell Labs and contributed to the design of the pioneering AWK and AMPL programming languages. ... Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (born September 9, 1941) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and Unix. ... A programming paradigm is a paradigmatic style of programming (compare with a methodology, which is a paradigmatic style of doing software engineering). ... 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 or section does not cite its references or sources. ... 1972 (MCMLXXII) was a leap year starting on Saturday. ... Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (born September 9, 1941) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and Unix. ... Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (born September 9, 1941) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and Unix. ... 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. ... 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. ... 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. ... In computing, weak typing, when applied to a programming language, is used to describe how the language handles datatypes. ... GCC may stand for: Gulf Cooperation Council GNU Compiler Collection (formerly, the GNU C Compiler) Garde côtière canadienne (Canadian Coast Guard) Germanna Community College Glendale Community College global carbon cycle Global Climate Coalition Grand Council of the Crees (gcc. ... Visual C++ 6. ... Turbo C is a Pantojas Integrated Development Environment and compiler for the C programming language. ... The Watcom C compiler was distinguished amongst DOS developers by the high execution speed of the compiled code it produced and for supporting intels 32bit 386 protected mode. ... 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... C++ (generally pronounced /si plʌs plʌs/) is a general-purpose, high-level programming language with low-level facilities. ... 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. ... CPL may stand for: The Cyberathlete Professional League: a professional e-sports league. ... ALGOL 68 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. ... It has been suggested that Assembler be merged into this article or section. ... The pascal (symbol: Pa) is the SI unit of pressure. ... AWK is a general purpose computer language that is designed for processing text based data, either in files or data streams. ... CSH is a three-letter abbreviation with multiple meanings: The United States Army operates combat support hospitals. ... C++ (generally pronounced /si plʌs plʌs/) is a general-purpose, high-level programming language with low-level facilities. ... 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... Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. ... JavaScript is the name of Netscape Communications Corporations implementation of ECMAScript, a scripting programming language based on the concept of prototypes. ... Image File history File links Wikibooks-logo-en. ... Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is part of the Wikimedia Foundation. ... This article or section does not cite its references or sources. ... 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. ... Computer programming (often simply programming or coding) is the craft of writing a set of commands or instructions that can later be compiled and/or interpreted and then inherently transformed to an executable that an electronic machine can execute or run. Programming requires mainly logic, but has elements of science... A programming language is an artificial language that can be used to control the behavior of a machine (often a computer). ... Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (born September 9, 1941) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and Unix. ... Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... C++ (generally pronounced /si plʌs plʌs/) is a general-purpose, high-level programming language with low-level facilities. ... System software is a generic term referring to any computer software whose purpose is to help run the computer system. ... Application software is a loosely defined subclass of computer software that employs the capabilities of a computer directly to a task that the user wishes to perform. ... Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ...

Contents


Philosophy

C is a minimalistic programming language. Among its design goals were that it could be compiled in a straightforward manner using a relatively simple compiler, provide low-level access to memory, generate only a few machine language instructions for each of its core language elements, and not require extensive run-time support. As a result, C code is suitable for many systems-programming applications that had traditionally been implemented in assembly language. A programming language is an artificial language that can be used to control the behavior of a machine (often a computer). ... A system of codes directly understandable by a computers CPU is termed this CPUs native or machine language. ... In computer science, run time (with a space, though often its spelled without one) describes the operation of a computer program, the duration of its execution, from beginning to termination (compare compile time). ... Systems programming (or system programming) is the activity of programming system software. ... It has been suggested that Assembler be merged into this article or section. ...


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 adaptation of a piece of software so that it will function in a different computing environment to that for which it was originally written. ...


Characteristics

As an Algol-based language, C has the following characteristics:

C also has the following specific properties: This article or section does not cite its references or sources. ... Structured programming can be seen as a subset or subdiscipline of procedural programming, one of the major programming paradigms. ... A lexicon is a list of words together with additional word-specific information, i. ... In computer programming in general, a scope is an enclosing context. ... A Sierpinski triangle —a confined recursion of triangles to form a geometric lattice. ... 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 this article or section be merged into Subroutine. ... It has been suggested that Software pointer be merged into this article or section. ... Look up Aggregate in Wiktionary, the free dictionary. ... 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 keyword is an identifier which indicates a specific command. ...

  • Weak typing — for instance, characters can be used as integers (similar to assembly)
  • Low-level access to computer memory via machine addresses and typed pointers
  • Function pointers allow for a rudimentary form of closures and runtime polymorphism
  • Array indexing as a secondary notion, defined in terms of pointer arithmetic
  • A standardized C preprocessor for macro definition, source code file inclusion, conditional compilation, etc.
  • A simple, small core language, with functionality such as mathematical functions and file handling provided by library routines
  • C discarded the well established logical connectives and and or of most other algol derivatives and replaced them with && and ||, which
    • Were invented in order to make bit-wise operations (& and |) syntactically distinct — C's predecessor B used & and | for both meanings
    • Never evaluate the right operand if the result can be determined from the left alone
  • C popularized the controversial decision to free the equal-sign for assignment use by replacing = with == (inherited from B).

C lacks features found in some other systems implementation languages: 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. ... It has been suggested that Software pointer be merged into this article or section. ... In programming languages, a closure is a function that refers to free variables in its lexical context. ... In computer science, polymorphism means allowing a single definition to be used with different types of data (specifically, different classes of objects). ... In computer programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... The C preprocessor (cpp) is the preprocessor for the C programming language. ... ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ... In computer science, a core language is a pure programming language, generally organized into statement blocks; the core language is often developed into libraries, which are then used during programming. ... Illustration of an application which may use libvorbisfile. ... B was the name of a programming language developed at Bell Labs. ...

  • No non-scalar operations such as copying of arrays or strings (old versions of C did not even copy structs automatically)
  • No automatic garbage collection
  • No bounds checking of arrays
  • No semi-dynamic (i.e. stacked, runtime-sized) arrays until the C99 standard (despite not requiring garbage collection)
  • No syntax for ranges, such as the A..B notation used in both newer and older languages
  • No nested function definitions (although some compilers provide them, for example, GCC)
  • No formal closures or functions as parameters (only function and variable pointers)
  • No generators or coroutines; intra-thread control flow consists of nested function calls, except for the use of the longjmp or setcontext library functions
  • No exception handling; standard library functions signify error conditions with the global errno variable and/or special return values
  • Rudimentary support for modular programming
  • No compile-time polymorphism in the form of function or operator overloading; only rudimentary support for generic programming
  • No support for object-oriented programming; in particular, no support for polymorphism, inheritance and limited (inter-module only) support for encapsulation, even though there are libraries offering object systems for C, and many object-oriented languages are themselves written in C
  • No native support for multithreading and networking, though these facilities are provided by popular libraries
  • No standard libraries for graphics and several other application programming needs

Although the list of built-in features C lacks is long, this has contributed significantly to its acceptance, as new C compilers can be developed quickly for new platforms. The relatively low-level nature of the language affords the programmer close control over what the program is doing, while allowing solutions that can be specially tailored and aggressively optimized for a particular platform. This allows the code to run efficiently on very limited hardware, such as mass-produced consumer embedded systems, which today are as capable as the general-purpose machines originally used to implement C. In computer science, garbage collection (also known as GC) is a form of automatic memory management. ... Look up range in Wiktionary, the free dictionary. ... A nested function is a function which can only be called from its parent function. ... The GNU Compiler Collection (usually shortened to GCC) is a set of programming language compilers produced by the GNU Project. ... In programming languages, a closure is a function that refers to free variables in its lexical context. ... 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. ... Modularity is a concept that has applications in the contexts of computer science, particularly programming, as well as cognitive science in investigating the structure of mind. ... 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. ... In computer science, overloading is a type of polymorphism where different functions with the same name are invoked based on the data types of the parameters passed. ... In computer science, generics is a technique that allows one value to take different datatypes (so-called polymorphism) as long as certain contracts such as subtypes and signature are kept. ... In computer science, object-oriented programming, OOP for short, is a computer programming paradigm. ... This article is about inheritance in object-oriented programming. ... 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. ... GUI can refer to the following: GUI is short for graphical user interface, a term used to describe a type of interface in computing. ... A compiler is a computer program that translates a computer program written in one computer language (called the source language) into an equivalent program written in another computer language (called the output or the target language). ... An embedded system is a special-purpose computer system, which is completely encapsulated by the device it controls. ...


A number of the above missing features are available through the use of third party libraries. In some cases, a missing feature can be approximated within C. For example, the original implementation of C++ consisted of a preprocessor that translated the C++ syntax into C source code. Most object oriented functions include a special "this" pointer, which refers to the current object. By passing this pointer as a function argument in C, the same functionality can be performed in C. For example, in C++ one might write:

 stack->push(val); 

while in C, one would write:

 push(stack,val); 

where the stack argument of C is a pointer to a struct which is equivalent to the this pointer of C++, which is a pointer to an object.


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. AT&T Inc. ... 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. ...


There are many legends as to the origin of C and the closely related Unix operating system, including these: Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ...

  • The development of Unix was the result of programmers' desire to play the Space Travel video-game. They had been playing it on their company's mainframe, but as it was underpowered and had to support about 100 users, Thompson and Ritchie found they did not have sufficient control over the spaceship to avoid collisions with the wandering space rocks. This led to the decision to port the game to an idle PDP-7 in the office. As this machine lacked an operating system, the two set out to develop one, based on several ideas from colleagues. Eventually it was decided to port the operating system to the office's PDP-11, but faced with the daunting task of translating a large body of custom-written assembly language code, the programmers began considering using a portable, high-level language so that the OS could be ported easily from one computer to another. They looked at using B, but it lacked functionality to take advantage of some of the PDP-11's advanced features. This led to the development of an early version of the C programming language.
  • The justification for obtaining the original computer to be used in developing the Unix operating system was to create a system to automate the filing of patents. The original version of the Unix system was developed in assembly language. Later, the entire operating system was rewritten in C, an unprecedented move at a time when nearly all operating systems were written in assembly.

By 1973, the C language had become powerful enough that most of the Unix kernel, originally written in PDP-11 assembly language, 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 Burroughs B5000 written in ALGOL in 1961.) This article is about computer and video games. ... Mainframes (often colloquially referred to as big iron) are large and expensive computers used mainly by government institutions and large companies for legacy applications, typically bulk data processing (such as censuses, industry/consumer statistics, ERP, and bank transaction processing). ... An asteroid is a predominantly rocky body that orbits around its star. ... DEC PDP-7 Minicomputer(circa 1965) A modified PDP-7 under restoration in Oslo, Norway The DEC PDP-7 is a minicomputer produced by Digital Equipment Corporation. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The PDP-11 was a 16-bit minicomputer sold by Digital Equipment Corp. ... It has been suggested that Assembler be merged into this article or section. ... Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... In computer science, the kernel is the fundamental part of an operating system. ... The PDP-11 was a 16-bit minicomputer sold by Digital Equipment Corp. ... 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 a computer programming language designed for scientific, engineering, and business applications. ... This article might not be written in the formal tone expected of an encyclopedia entry. ... Background The B5000 was designed in 1961 by a team at Burroughs under the leadership of Robert (Bob) Barton. ... ALGOL (short for ALGOrithmic Language) is a family of imperative computer programming languages originally developed in the mid 1950s which became the de facto standard way to report algorithms in print for almost the next 30 years. ...


K&R C

In 1978, Dennis Ritchie and Brian Kernighan 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. Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (born September 9, 1941) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and Unix. ... Brian Wilson Kernighan (pronounced Ker-ni-han; the g is silent; born 1942) is a computer scientist who worked at the Bell Labs and contributed to the design of the pioneering AWK and AMPL programming languages. ... The C Programming Language, by Brian Kernighan and Dennis Ritchie; one of the most read and trusted books on C. The C Programming Language, 1st edition, also known as the Old Testament. The C Programming Language (also known as K&R or the white book) is a famous computer science... In engineering and manufacturing, the term specification has the following meanings: Technical requirement A specification is a set of requirements. ... ANSI C (Standard C) is a variant of the C programming language. ...


K&R introduced several language features:

  • struct data types
  • long int data type
  • unsigned int data type
  • The =- operator was changed to -= to remove the semantic ambiguity created by the construct i=-10, which could be interpreted as either i =- 10 or i = -10

For many years after the introduction of ANSI C, 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 ANSI 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.


For example:

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

In the example, both SomeFunction and OtherFunction were declared before use. In K&R, OtherFunction declaration could be omitted.


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 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 (since there was no standard), supported by compilers from AT&T and some other vendors. These included:

The large number of extensions and lack of 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. ... In most imperative computer programming languages, the assignment statement is one of the basic statements. ... Const-correctness is a programming language feature that allows the programmer to indicate when an object can and cannot change by declaring the object const (or non-const). ... In computer programming, an enumerated type is a data type whose set of values is a finite list of identifiers chosen by the programmer. ... 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

The C Programming Language, 2nd edition, is a widely used reference on ANSI C.
The C Programming Language, 2nd edition, is a widely used reference on ANSI C.

During the late 1970s, C began to replace BASIC as the leading microcomputer programming language. During the 1980s, it was adopted for use with the IBM PC, and its popularity began to increase significantly. At the same time, Bjarne Stroustrup and others at Bell Labs began work on adding object-oriented programming language constructs to C, resulting in the language now called C++. Download high resolution version (559x739, 98 KB)Cover photo of K&R (ANSI version, ISBN 0-131-10362-8), photo by myself, This image is a book cover. ... Download high resolution version (559x739, 98 KB)Cover photo of K&R (ANSI version, ISBN 0-131-10362-8), photo by myself, This image is a book cover. ... BASIC (Beginners All-purpose Symbolic Instruction Code) is a family of high-level programming languages. ... The Commodore 64 was one of the most popular microcomputers of its era, and is the best selling home computer of all time. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... Bjarne Stroustrup Bjarne Stroustrup (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. ... C++ (generally pronounced /si plÊŒs plÊŒs/) is a general-purpose, high-level programming language with low-level facilities. ...


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. ... ANSI C (Standard C) is a variant of 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. The International Organization for Standardization (ISO) is an international standard-setting body composed of representatives from national standards bodies. ...


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 a more capable preprocessor. The syntax for parameter declarations was also augmented to include the C++ style: 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 set 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 transmission of text through telecommunication networks. ... 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. ...

 int main(int argc, char **argv) { ... } 

although the K&R interface

 int main(argc, argv) int argc; char **argv; { ... } 

continued to be permitted, for compatibility with existing source code.


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. ... This article or section needs a complete rewrite for the reasons listed on the talk page. ... When integers or any other data are represented with multiple bytes, there is no unique way of ordering of those bytes in memory or in a transmission over some medium, and so the order is subject to arbitrary convention. ...


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, in order to take advantage of features available only in Standard C.

 #ifdef __STDC__ extern int getopt(int,char * const *,const char *); #else extern int getopt(); #endif 

In the above example, a compiler which has defined the __STDC__ macro (as mandated by the C standard) only interprets the line following the ifdef command. In other, nonstandard compilers which don't define the macro, only the line following the else command is interpreted.


C99

Note: C99 is also the name of a C compiler for the Texas Instruments TI-99/4A home computer. Aside from being a C compiler, it is otherwise unrelated.

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 9899:1999 in 1999. This standard is commonly referred to as "C99." It was adopted as an ANSI standard in March 2000. Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is an American company based in Dallas, Texas, USA, renowned for developing and commercializing semiconductor and computer technology. ... The Texas Instruments TI-99/4A was an early home computer, released in June 1981, originally at a price of $525. ... C++ (generally pronounced /si plÊŒs plÊŒs/) is a general-purpose, high-level programming language with low-level facilities. ...


C99 introduced several new features, many of which had already been implemented as extensions in several compilers:

  • Inline functions
  • Variables can be declared anywhere (as in C++), rather than only after another declaration or the start of a compound statement
  • Several new data types, including long long int, an explicit boolean data type, and a complex type to represent complex numbers
  • Variable-length arrays
  • Support for one-line comments beginning with //, as in BCPL or C++
  • New library functions, such as snprintf
  • New header files, such as stdbool.h and inttypes.h
  • Type-generic math functions (tgmath.h)
  • Improved support for IEEE floating point
  • Designated initializers
  • Compound literals
  • Support for variadic macros (macros of variable arity)
  • restrict qualification to allow more aggressive code optimization

C99 is for the most part upward-compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. The C standards committee decided that it was of more value for compilers to diagnose inadvertent omission of the type specifier than to silently process legacy code that relied on implicit int. In practice, compilers are likely to diagnose the omission but also assume int and continue translating the program. 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 computer science and mathematics, a variable (sometimes called a pronumeral) is a symbol denoting a quantity or symbolic representation. ... Data type is a type of data in a type system in computer programming. ... In computer science the boolean datatype, sometimes called the logical datatype, is a primitive datatype having two values: one and zero (sometimes called true and false). ... Wikibooks Algebra has more about this subject: Complex numbers In mathematics, a complex number is an expression of the form where a and b are real numbers, and i is a specific imaginary number, called the imaginary unit, with the property i 2 = −1. ... In computer programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... 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. ... 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. ... The IEEE Standard for Binary Floating-Point Arithmetic (IEEE 754) is the most widely-used standard for floating-point computation, and is followed by many CPU and FPU implementations. ... In mathematics and computer programming the arity of a function or an operator is the number of arguments or operands it takes (arity is sometimes referred to as valency, although that actually refers to another meaning of valency in mathematics). ... It has been suggested that Loop optimization be merged into this article or section. ...


GCC and other C compilers now support many of the new features of C99. However, there has been less support from vendors such as Microsoft and Borland that have mainly focused on C++, since C++ provides similar functionality in sometimes incompatible ways (e.g., the complex template class). Microsoft's Brandon Bray said "In general, we have seen little demand for many C99 features. Some features have more demand than others, and we will consider them in future releases provided they are compatible with C++." [1] The GNU Compiler Collection (usually shortened to GCC) is a set of programming language compilers produced by the GNU Project. ... It has been suggested that Criticism of Microsoft be merged into this article or section. ... Borland Software Corporation is a software company headquartered in California. ...


GCC, despite its extensive C99 support, is still not a completely compliant implementation; several key features are missing or don't work correctly.[2]


Usage

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. This is implemented in one of two ways, as languages which: In computer science, an intermediate language is the language of an abstract machine designed to aid in the analysis of computer programs. ...

  • Can output object code, machine code, or another representation (e.g., bytecodes), and C source code. Examples: some Lisp dialects, Squeak's C-subset Slang.
  • Do not output object code, machine code, or another representation, but output C source code only. Examples: Eiffel, Sather; Esterel.

C source code is then input to a C compiler, which then outputs finished object or machine code. This is done to gain portability (C compilers exist for nearly all platforms) and to avoid having to develop machine-specific code generators. 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. ... A system of codes directly understandable by a computers CPU is termed this CPUs native or machine language. ... Byte-code is a sort of intermediate code that is more abstract than machine code. ... The Squeak programming language is a Smalltalk implementation, derived directly from Smalltalk-80, by Smalltalks originators, so it is object-oriented, and reflective. ... Eiffel is an object-oriented programming language which emphasizes the production of robust software. ... Sather is an object-oriented programming language. ... Esterel is a formally defined synchronous imperative language for the programming of reactive systems. ...


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

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. ... 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, as well as the pointer-to symbol *, specify built-in types. Sections of code are enclosed in braces ({ and }) to indicate the extent to which declarations and control structures apply. Various brackets in Arial // In writing Brackets are punctuation marks, used in pairs to set apart or interject text within other text. ...


As an imperative language, C depends on statements to do most of the work. Most statements are expression statements which simply evaluate an expression; as a side effect, variables may receive new values. Control-flow statements are also available for conditional or iterative execution, constructed with reserved keywords such as if, else, switch, do, while, and for. Arbitrary jumps are possible with goto. A variety of built-in operators perform primitive arithmetic, Boolean logical, comparative, bitwise logical, and array indexing operations and assignment. Expressions can also invoke functions, including a large number of standard library functions, for performing many common tasks. The adjective Boolean (sometimes boolean), coined in honor of George Boole, is used in many contexts: An evaluation that results in either TRUE or FALSE. A boolean value is a truth value, either true or false, often coded 1 and 0, respectively. ...


"hello, world" example

The following simple application appeared in the first edition of K&R, and 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. However, it might be a file or some other hardware device, depending on how standard output is mapped at the time the program is executed.
The C Programming Language, by Brian Kernighan and Dennis Ritchie; one of the most read and trusted books on C. The C Programming Language, 1st edition, also known as the Old Testament. The C Programming Language (also known as K&R or the white book) is a famous computer science... A hello world program is a software program that prints out Hello, world! on a display device. ... 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. ...

 main() { printf("hello, worldn"); } 

The above program will compile correctly on most modern compilers that are not in compliance mode. However, it produces several warning messages when compiled with a compiler that conforms to the ANSI C standard, and won't compile at all if the compiler strictly conforms to the C99 standard. The current, ANSI C or C99, "hello world" program is written as follows: ANSI C (Standard C) is a variant of the C programming language. ...

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

What follows is a line-by-line analysis of the above program:

 #include <stdio.h> 

This first line of the program is a preprocessing directive, #include. This causes the preprocessor — the first tool to examine source code when it is compiled — to substitute for that line the entire text of the file to which it refers. In this case, the header stdio.h, which contains declarations for standard input and output functions such as printf, will replace that line. 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 implementation, and double quotes for local or installation-specific headers. Preprocessing is the act of processing data before it is parsed. ...

 int main(void) 

This next line indicates that a function named main is being defined. The main function serves a special purpose in C programs: When the program is executed, main is the function called by the run-time environment—otherwise it acts like any other function in the program. 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) in between the parentheses indicates that the main function takes no arguments. See also void. In some programming languages, the main function is where a program starts execution. ... In various programming languages, a void return type indicates that a function does not return a value. ...

 { 

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

 printf("hello, worldn"); 

This 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 beginning of the next line. The return value of the printf function is of type int, but no use was made of it so it will be quietly discarded. (A more careful program might test this value to determine whether the operation succeeded.) Several programming languages implement a printf function, to output a formatted string. ... Illustration of an application which may use libvorbisfile. ... In computer programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... In computing, a newline is a special character or sequence of characters signifying the end of a line of text. ...

 return 0; 

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

 } 

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


If the above code were compiled and executed, it would do the following:

  • Print the string "hello, world" onto the standard output device (typically but not always a terminal),
  • Move the current position indicator to the beginning of the next line, then
  • Return a "successful" exit status to the calling process (such as a command shell or script).

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). 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. ... ALGOL (short for ALGOrithmic Language) is a family of imperative computer programming languages originally developed in the mid 1950s which became the de facto standard way to report algorithms in print for almost the next 30 years. ... Pascal is an 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 programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... 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. (The use of type casts obviously sacrifices some of the safety normally provided by the type system.) In computer science, type conversion or typecasting refers to changing an entity of one datatype into another. ...


Pointers

C allows 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 the data stored at the address pointed to, or to invoke the pointed-to function. Pointers can be manipulated using normal assignments and also pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address, 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. Pointers to functions are useful for callbacks from event handlers. This article discusses 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 some branches of mathematics, strings are sequences of various simple objects. ... 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 computer science, a callback is executable code that is passed as a parameter to other code. ...


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. Void pointers (void *) also exist and 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 possible, although they can easily be (and in fact implicitly are) converted to and from any other object pointer type. 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 used in computer programming. ...


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 (see the "Criticism" article), and can lead to various repercussions: illegal memory accesses, corruption of data, buffer overrun, run-time exceptions, etc. In computer programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... The C programming language is a very widely used programming language, minimalistic and low-level by design. ...


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. ...


Array↔pointer interchangeability

A unique (and 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 contexts (sizeof array being a notable exception), 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 discusses a general notion of reference in computing. ...


The number of elements in an array a can be determined as sizeof a / sizeof a[0], provided that the name is "in scope" (visible).


An interesting demonstration of the remarkable interchangeability of pointers and arrays is shown below. These four lines 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[i] = 1; *(x + i) = 1; *(i + x) = 1; i[x] = 1; /* strange, but correct */ 

There is, however, a distinction to be made between arrays and pointer variables. Even though the name of an array is in most 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 can be 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 has a small amount of overhead during initialization, 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. Unlike dynamic memory allocation where memory is allocated as required at run-time, static memory allocation refers to the process of allocating memory at compile-time; before the associated program is executed. ... In computer science and mathematics, a variable (sometimes called a pronumeral) is a symbol denoting a quantity or symbolic representation. ... 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 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 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 hassle of manually allocating and releasing storage. Unfortunately, many data structures can grow in size at runtime; since automatic and static allocations must have a fixed size at compile-time, there are many situations in which dynamic allocation must be used. Variable-sized arrays are 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 standard library for performing dynamic memory allocation. ...


Libraries

The C programming language uses libraries as its primary method of extension. In C, a library is a collection of functions contained within a single 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, the header file from that library must be declared at the top of a source file, and the library must be linked to the program, which in many cases requires compiler flags (e.g., -lmath). 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. ...


The most common C library is the C standard library, which is specified by the ISO and ANSI C standard and comes standard with every modern C compiler. 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. ... ISO has many meanings: Iso is the stem of the Latin transliteration of the Greek word ίσος (ísos, meaning equal). The iso- prefix in English derives from this and means equality or similarity. ... 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. Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... 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. ... In computer science, the kernel is the fundamental part of an operating system. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... 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 generates 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 is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. ... Perl, also Practical Extraction and Report Language (a backronym, see below) is a dynamic procedural programming language designed by Larry Wall and first released in 1987. ... Python is an interpreted programming language created by Guido van Rossum in 1990. ...


Criticism

Despite its popularity, C has been widely criticized. Such criticisms fall into two broad classes: desirable operations that are too hard to achieve using unadorned C, and undesirable operations that are too easy to accidentally achieve while using C. Putting this another way, the safe, effective use of C requires more programmer skill, experience, effort, and care than is required for some other programming languages. Several of these criticisms are summarized in the article "C programming language, criticism". The C programming language is a very widely used programming language, minimalistic and low-level by design. ...


Tools for mitigating issues with C

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. 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, and automatic garbage collection, that are not a standard part of C. In computer security and programming, a buffer overflow, or buffer overrun, is an anomalous condition where a process attempts to store data beyond the boundaries of a buffer. ... In computer science, garbage collection (also known as GC) is a form of automatic memory management. ...


Many compilers, most notably Visual C++, deal with the long compilation times inflicted by header file inclusion using precompiled headers, a system where declarations are stored in an intermediate format that is quick to parse. Building the precompiled header files in the first place is expensive, but this is generally done only for system header files, which are larger and more numerous than most application header files and also change much less often.


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.


It should be recognized that these tools are not a panacea. Because of C's flexibility, some types of errors involving misuse of variadic functions, out-of-bounds array indexing, and incorrect memory management cannot be detected on some architectures without incurring a significant performance penalty. However, some common cases can be recognized and accounted for.


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++ (generally pronounced /si plÊŒs plÊŒs/) is a general-purpose, high-level programming language with low-level facilities. ... 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...


C++

The C++ programming language was derived from C and is Bjarne Stroustrup's answer to adding 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. Considered nearly a superset of C, C++ supports most of C, with a few relevant exceptions (mostly of stronger typing restriction; see Compatibility of C and C++ for an exhaustive list of differences). C++ (generally pronounced /si plÊŒs plÊŒs/) is a general-purpose, high-level programming language with low-level facilities. ... Bjarne Stroustrup Bjarne Stroustrup (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. ... In computer science, generics is a technique that allows one value to take different datatypes (so-called polymorphism) as long as certain contracts such as subtypes and signature are kept. ... The C and C++ programming languages are closely related, as C++ grew out of C and is many ways a superset of the latter. ...


Objective-C

Objective-C is a very "thin" layer on top of and 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 is taken from Smalltalk. Objective-C and C++ differ in philosophies -- see the Objective-C article for details. 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... Smalltalk is an object-oriented, dynamically typed, reflective programming language designed at Xerox PARC by Alan Kay, Dan Ingalls, Ted Kaehler, Adele Goldberg, and others during the 1970s, influenced by Sketchpad and Simula. ... 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...


See also

The C preprocessor (cpp) is the preprocessor for the C programming language. ... 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. ... 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 programming language has an extensive system for declaring variables of different types. ... Programming languages are used for controlling the behavior of a machine (often a computer). ... C++ (generally pronounced /si plÊŒs plÊŒs/) is a general-purpose, high-level programming language with low-level facilities. ... The title given to this article is incorrect due to technical limitations. ... 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. ... 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... This is a list of operators in the C++ and C programming languages. ... A programming tool is a program or application that software developers use to create, debug, or maintain other programs and applications. ... Cygwin is a collection of free software tools originally developed by Cygnus Solutions to allow various versions of Microsoft Windows to act somewhat like a Unix system. ... Dev-C++ is a free IDE (integrated development environment) for programming use in C and its derivative, C++. Dev-C++ is bundled with the open source MinGW compiler utilizing gcc and its C++ counterpart, g++. Dev-C++ is distributed under the GNU General Public License. ... DJGPP is a 32-bit C/C++ development system for 386 and above PCs that runs under DOS (it will also work in a DOS window from within an operating system that supports DOS windows, such as Windows). ... The GNU Compiler Collection (usually shortened to GCC) is a set of programming language compilers produced by the GNU Project. ... LCC (Local C Compiler) is a small retargetable ANSI C compiler developed by Chris Fraser and David Hanson. ... Figure of the linking process, where object files and static libraries are assembled into a new library or executable. ... The correct title of this article is make. ... Lint is the name of a Wolf that used to Bum other wolfs while Grey ctas filmed them with thier camera Phones. ... In computing, Small-C is both a subset of the C programming language, suitable for resource-limited microcomputers and embedded systems, and an implementation of that subset. ... 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... // C vs Pascal: A language comparison C and Pascal are both arguably descendants of the ALGOL programming language series. ... C to Java Virtual Machine compilers attempt to marry the highly popular C language with the platform independent Java Virtual Machine for Write Once Run Anywhere (WORA) using the C language. ...

Footnotes

  1. ^ See Generational list of programming languages
  2. ^ 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.
  3. ^ Choosing the right programming language. Wikibooks (2006). Retrieved on 2006-07-18.

Here, a genealogy of programming languages is shown. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... July 18 is the 199th day (200th in leap years) of the year in the Gregorian Calendar, with 166 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... July 18 is the 199th day (200th in leap years) of the year in the Gregorian Calendar, with 166 days remaining. ...

References

  • Brian Kernighan, Dennis Ritchie: The C Programming Language. Also known as K&R — The original book on C.
    • 1st, Prentice Hall 1978; ISBN 0-131-10163-3. Pre-ANSI C.
    • 2nd, Prentice Hall 1988; ISBN 0-131-10362-8. ANSI C.
  • ISO/IEC 9899. The official C:1999 standard, along with technical corrigenda and a rationale. As of 2005 the latest version is ISO/IEC 9899:TC2.
  • 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.
    • 4th, Prentice Hall 1994; ISBN 0-133-26224-3.
    • 5th, Prentice Hall 2002; ISBN 0-130-89592-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 (pronounced Ker-ni-han; the g is silent; born 1942) is a computer scientist who worked at the Bell Labs and contributed to the design of the pioneering AWK and AMPL programming languages. ... Ken Thompson (left) with Dennis Ritchie (right) Dennis MacAlistair Ritchie (born September 9, 1941) is a computer scientist notable for his influence on ALTRAN, B, BCPL, C, Multics, and Unix. ... The C Programming Language, by Brian Kernighan and Dennis Ritchie; one of the most read and trusted books on C. The C Programming Language, 1st edition, also known as the Old Testament. The C Programming Language (also known as K&R or the white book) is a famous computer science... Guy Lewis Steele, Jr. ... A diagram of the operation of a typical multi-language compiler. ... 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 term for the following books on algorithms and numerical analysis, all by William Press, Saul Teukolsky, William Vetterling and Brian Flannery: Numerical Recipes in C++. The Art of Scientific Computing, ISBN 0-521-75033-4. ...

External links

Tutorials

  • C Programming at Wikibooks
  • Everything You Ever Wanted to Know about C Types
  • C Programming (course at University of Strathclyde Computer Centre)
  • The C Book by M.Banahan-D.Brady-M.Doran (Addison-Wesley, 2nd ed.) — A very interesting and complete book for beginners/intermediate, now off-print and free.
  • C Unleashed by Richard Heathfield and others contributors in comp.lang.c (Sams) — An interesting book about advanced ISO-C.
  • Essential C — Short C guide, great for programmers new to C.
  • Everything you need to know about pointers in C

Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is part of the Wikimedia Foundation. ...

Resources

  • Basic concepts in the C language
  • ISO C Working Group (official Web site)
  • comp.lang.c Frequently Asked Questions
  • comp.lang.c Wiki
  • GNU C Library documentary (can also download source files)
  • Programming in C (document collection at Lysator)
  • The New C Standard: An economic and cultural commentary — An unpublished book about "detailed analysis of the International Standard for the C language. (PDF)"

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Optimization techniques

  • Programming Optimization
  • C optimization tutorial

C99

  • The current Standard (C99 with Technical corrigenda TC1 and TC2 included) - in PDF
  • Open source development using C99 — Is your C code up to standard? by Peter Seebach
  • Are you Ready For C99?

Support

  • C Forum at Cprogramming.com
  • C and C++ at Daniweb

History


  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.
  More results at FactBites »

 
 

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