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Not to exist confused with C++.

Full general-purpose programming linguistic communication

C

The C Programming Linguistic communication [ane] (often referred to as K&R), the seminal volume on C
Paradigm	Multi-epitome: imperative (procedural), structured
Designed by	Dennis Ritchie
Developer	Dennis Ritchie & Bong Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
First appeared	1972; fifty years ago  (1972) [two]
Stable release	C17 / June 2018; 3 years agone  (2018-06)
Preview release	C2x (N2731) / October xviii, 2021; 4 months agone  (2021-10-eighteen) [3]
Typing discipline	Static, weak, manifest, nominal
Os	Cross-platform
Filename extensions	.c, .h
Website	www.iso.org/standard/74528.html www.open-std.org/jtc1/sc22/wg14/
Major implementations
pcc, GCC, Clang, Intel C, C++Builder, Microsoft Visual C++, Watcom C
Dialects
Cyclone, Unified Parallel C, Separate-C, Cilk, C*
Influenced by
B (BCPL, CPL), ALGOL 68,[4] assembly, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Go, Java, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Pike, Processing, Python, Ring,[5]Rust, Seed7, Vala, Verilog (HDL),[vi] Nim, Zig
C Programming at Wikibooks

C (, as in the letter c) is a general-purpose, procedural computer programming language supporting structured programming, lexical variable scope, and recursion, with a static type arrangement. By design, C provides constructs that map efficiently to typical car instructions. It has found lasting use in applications previously coded in assembly linguistic communication. Such applications include operating systems and diverse application software for computer architectures that range from supercomputers to PLCs and embedded systems.

A successor to the programming linguistic communication B, C was originally developed at Bell Labs by Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating arrangement.^[7] During the 1980s, C gradually gained popularity. It has become one of the nearly widely used programming languages,^{[eight] [9]} with C compilers from various vendors available for the majority of existing estimator architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and by the International Organization for Standardization (ISO).

C is an imperative procedural language. Information technology was designed to be compiled to provide low-level access to retentiveness and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C programme written with portability in mind tin can be compiled for a wide diversity of computer platforms and operating systems with few changes to its source code.^[ten]

Since 2000, C has consistently ranked among the top two languages in the TIOBE alphabetize, a measure of the popularity of programming languages.^[eleven]

Overview [edit]

Similar most procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type system prevents unintended operations. In C, all executable code is independent within subroutines (as well called "functions", though non strictly in the sense of functional programming). Function parameters are always passed past value (except arrays). Pass-by-reference is simulated in C by explicitly passing pointer values. C programme source text is complimentary-format, using the semicolon as a statement terminator and curly braces for group blocks of statements.

The C language too exhibits the following characteristics:

• The linguistic communication has a small, fixed number of keywords, including a full gear up of control flow primitives: if/else, for, do/while, while, and switch. User-defined names are non distinguished from keywords by any kind of sigil.
• It has a large number of arithmetic, bitwise, and logic operators: +,+=,++,&,||, etc.
• More than than ane assignment may be performed in a single statement.
• Functions:
  • Office return values tin be ignored, when not needed.
  • Part and data pointers permit advertisement hoc run-time polymorphism.
  • Functions may not be defined within the lexical scope of other functions.
• Data typing is static, simply weakly enforced; all data has a type, but implicit conversions are possible.
• Annunciation syntax mimics usage context. C has no "define" keyword; instead, a statement kickoff with the proper noun of a type is taken as a proclamation. In that location is no "function" keyword; instead, a function is indicated by the presence of a parenthesized argument listing.
• User-divers (typedef) and compound types are possible.
  • Heterogeneous aggregate data types (struct) allow related information elements to be accessed and assigned equally a unit of measurement.
  • Union is a structure with overlapping members; only the final member stored is valid.
  • Assortment indexing is a secondary annotation, defined in terms of pointer arithmetic. Unlike structs, arrays are not get-go-class objects: they cannot exist assigned or compared using single born operators. There is no "array" keyword in use or definition; instead, square brackets indicate arrays syntactically, for instance month[11].
  • Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
  • Strings are not a singled-out information type, but are conventionally implemented as null-terminated graphic symbol arrays.
• Low-level access to calculator retention is possible past converting machine addresses to typed pointers.
• Procedures (subroutines non returning values) are a special case of function, with an untyped return blazon void.
• A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
• There is a basic form of modularity: files tin be compiled separately and linked together, with control over which functions and data objects are visible to other files via static and extern attributes.
• Complex functionality such as I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does not include sure features found in other languages (such as object orientation and garbage collection), these can be implemented or emulated, often through the use of external libraries (e.g., the GLib Object System or the Boehm garbage collector).

Relations to other languages [edit]

Many afterward languages have borrowed directly or indirectly from C, including C++, C#, Unix's C shell, D, Become, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruddy, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[6] These languages have fatigued many of their command structures and other basic features from C. Most of them (Python being a dramatic exception) also limited highly similar syntax to C, and they tend to combine the recognizable expression and argument syntax of C with underlying type systems, data models, and semantics that can be radically different.

History [edit]

Early developments [edit]

Timeline of language evolution

Yr	C Standard[10]
1972	Birth
1978	Thou&R C
1989/1990	ANSI C and ISO C
1999	C99
2011	C11
2017	C17
TBD	C2x

The origin of C is closely tied to the development of the Unix operating organization, originally implemented in associates language on a PDP-7 by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Eventually, they decided to port the operating system to a PDP-11. The original PDP-eleven version of Unix was too developed in associates linguistic communication.^[7]

Thompson desired a programming language to brand utilities for the new platform. At outset, he tried to make a Fortran compiler, but before long gave up the idea. Instead, he created a cut-down version of the recently developed BCPL systems programming language. The official description of BCPL was non available at the fourth dimension,^[12] and Thompson modified the syntax to exist less wordy, producing the similar simply somewhat simpler B.^[7] However, few utilities were ultimately written in B because it was as well boring, and B could non have advantage of PDP-xi features such as byte addressability.

In 1972, Ritchie started to better B, most notably adding data typing for variables, which resulted in creating a new language C.^[13] The C compiler and some utilities made with it were included in Version 2 Unix.^[xiv]

At Version 4 Unix, released in November 1973, the Unix kernel was extensively re-implemented in C.^[7] By this time, the C language had acquired some powerful features such as struct types.

The preprocessor was introduced around 1973 at the urging of Alan Snyder and too in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I. Its original version provided but included files and uncomplicated string replacements: #include and #define of parameterless macros. Before long after that, information technology was extended, mostly by Mike Lesk and and then by John Reiser, to contain macros with arguments and conditional compilation.^[7]

Unix was one of the first operating system kernels implemented in a linguistic communication other than assembly. Earlier instances include the Multics arrangement (which was written in PL/I) and Master Command Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In effectually 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served equally the footing for several implementations of C on new platforms.^[thirteen]

K&R C [edit]

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Linguistic communication.^[1] This book, known to C programmers equally K&R, served for many years every bit an informal specification of the language. The version of C that information technology describes is commonly referred to as "K&R C". As this was released in 1978, it is also referred to as C78.^[15] The second edition of the book^[16] covers the later ANSI C standard, described below.

K&R introduced several language features:

• Standard I/O library
• long int data type
• unsigned int information type
• Compound assignment operators of the grade =op (such as =-) were changed to the form op= (that is, -=) to remove the semantic ambiguity created by constructs such every bit i=-10, which had been interpreted as i =- x (decrement i by 10) instead of the possibly intended i = -10 (permit i exist −10).

Even subsequently the publication of the 1989 ANSI standard, for many years K&R C was nevertheless 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 lawmaking can be legal Standard C also.

In early on versions of C, only functions that render types other than int must exist alleged if used earlier the function definition; functions used without prior declaration were presumed to return type int.

For example:

                        long                                    some_function            ();                        /* int */                                    other_function            ();                        /* int */                                    calling_function            ()                        {                                                long                                    test1            ;                                                annals                                    /* int */                                    test2            ;                                                test1                                    =                                    some_function            ();                                                if                                    (            test1                                    >                                    1            )                                                test2                                    =                                    0            ;                                                else                                                test2                                    =                                    other_function            ();                                                return                                    test2            ;                        }                      

The int type specifiers which are commented out could be omitted in K&R C, but are required in afterward standards.

Since Grand&R function declarations did not include whatsoever information about office arguments, function parameter type checks were not performed, although some compilers would event 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. Split tools such as Unix's lint utility were adult that (amidst other things) could check for consistency of function utilize across multiple source files.

In the years following the publication of Grand&R C, several features were added to the language, supported by compilers from AT&T (in particular PCC^[17]) and some other vendors. These included:

• void functions (i.due east., functions with no render value)
• functions returning struct or union types (rather than pointers)
• assignment for struct information types
• enumerated types

The large number of extensions and lack of agreement on a standard library, together with the language popularity and the fact that non fifty-fifty the Unix compilers precisely implemented the Thou&R specification, led to the necessity of standardization.

ANSI C and ISO C [edit]

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, equally its popularity began to increase significantly.

In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to found a standard specification of C. X3J11 based the C standard on the Unix implementation; still, the non-portable portion of the Unix C library was handed off to the IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified every bit ANSI X3.159-1989 "Programming Linguistic communication C". This version of the linguistic communication is oftentimes referred to as ANSI C, Standard C, or sometimes C89.

In 1990, the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) every bit ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language.

ANSI, similar other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained by the working group ISO/IEC JTC1/SC22/WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication.

One of the aims of the C standardization process was to produce a superset of Grand&R C, incorporating many of the subsequently introduced unofficial features. The standards committee likewise included several boosted features such as part prototypes (borrowed from C++), void pointers, back up for international character sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the style used in C++, the Chiliad&R interface continued to be permitted, for compatibility with existing source code.

C89 is supported past current C compilers, and most modern C code is based on information technology. Whatever programme written simply in Standard C and without whatever hardware-dependent assumptions will run correctly on whatever platform with a befitting C implementation, within its resource limits. Without such precautions, programs may compile only on a sure platform or with a particular compiler, due, for instance, 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 information types and byte endianness.

In cases where code must be compilable past 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 forestall the utilize on a K&R C-based compiler of features bachelor only in Standard C.

After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive support for international graphic symbol sets.^[18]

C99 [edit]

Main article: C99

The C standard was further revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to as "C99". It has since been amended three times by Technical Corrigenda.^[19]

C99 introduced several new features, including inline functions, several new data types (including long long int and a complex blazon to stand for complex numbers), variable-length arrays and flexible array members, improved support for IEEE 754 floating point, back up for variadic macros (macros of variable arity), and support for one-line comments beginning with //, equally in BCPL or C++. Many of these had already been implemented equally extensions in several C compilers.

C99 is for the most part backward compatible with C90, just 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 back up is available. GCC, Solaris Studio, and other C compilers at present support many or all of the new features of C99. The C compiler in Microsoft Visual C++, however, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.^{[twenty] [ needs update ]}

In improver, support for Unicode identifiers (variable / office names) in the form of escaped characters (e.g. \U0001f431) is now required. Support for raw Unicode names is optional.

C11 [edit]

In 2007, work began on another revision of the C standard, informally chosen "C1X" until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested by existing implementations.

The C11 standard adds numerous new features to C and the library, including blazon generic macros, anonymous structures, improved Unicode back up, atomic operations, multi-threading, and bounds-checked functions. Information technology also makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__ is defined as 201112L to indicate that C11 back up is available.

C17 [edit]

Published in June 2018, C17 is the current standard for the C programming language. It introduces no new linguistic communication features, just technical corrections, and clarifications to defects in C11. The standard macro __STDC_VERSION__ is defined as 201710L.

C2x [edit]

Master article: C2x

C2x is an informal name for the next (after C17) major C language standard revision. It is expected to be voted on in 2023 and would therefore exist chosen C23.^{[21] [ better source needed ]}

Embedded C [edit]

Historically, embedded C programming requires nonstandard extensions to the C language in order to back up exotic features such as fixed-betoken arithmetic, multiple distinct retentiveness banks, and bones I/O operations.

In 2008, the C Standards Committee published a technical study extending the C language^[22] to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as stock-still-point arithmetic, named address spaces, and bones I/O hardware addressing.

Syntax [edit]

C has a formal grammar specified by the C standard.^[23] Line endings are generally not meaning in C; withal, line boundaries do have significance during the preprocessing phase. Comments may appear either between the delimiters /* and */, or (since C99) following // until the cease of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as annotate delimiters if they announced within string or graphic symbol literals.^[24]

C source files comprise declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either ascertain new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, ordinarily past writing the type followed by the variable proper name. Keywords such every bit char and int specify born types. Sections of lawmaking are enclosed in braces ({ and }, sometimes chosen "curly brackets") to limit the scope of declarations and to deed equally a single statement for control structures.

As an imperative linguistic communication, C uses statements to specify actions. The most mutual statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side event 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 command-menses statements identified by reserved keywords. Structured programming is supported by if … [else] provisional execution and by practice … while, while, and for iterative execution (looping). The for statement has split up initialization, testing, and reinitialization expressions, whatever or all of which can be omitted. interruption and continue can be used to go out the innermost enclosing loop statement or skip to its reinitialization. There is likewise a non-structured goto argument which branches directly to the designated characterization within the function. switch selects a instance to be executed based on the value of an integer expression.

Expressions can employ a variety of built-in operators and may contain function calls. The society in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may fifty-fifty be interleaved. However, all side effects (including storage to variables) will occur before the next "sequence point"; sequence points include the finish of each expression statement, and the entry to and return from each role telephone call. Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a loftier caste of object code optimization by the compiler, just requires C programmers to take more care to obtain reliable results than is needed for other programming languages.

Kernighan and Ritchie say in the Introduction of The C Programming Language: "C, similar any other linguistic communication, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be amend."^[25] The C standard did non endeavour to right many of these blemishes, because of the bear upon of such changes on already existing software.

Character set [edit]

The basic C source character set includes the following characters:

• Lowercase and uppercase letters of ISO Basic Latin Alphabet: a–z A–Z
• Decimal digits: 0–9
• Graphic characters: ! " # % & ' ( ) * + , - . / : ; < = > ? [ \ ] ^ _ { | } ~
• Whitespace characters: space, horizontal tab, vertical tab, form feed, newline

Newline indicates the finish of a text line; information technology demand non correspond to an actual single graphic symbol, although for convenience C treats it every bit ane.

Additional multi-byte encoded characters may be used in cord literals, merely they are not entirely portable. The latest C standard (C11) allows multi-national Unicode characters to be embedded portably within C source text by using \uXXXX or \UXXXXXXXX encoding (where the X denotes a hexadecimal grapheme), although this characteristic is not nonetheless widely implemented.

The basic C execution character set contains the same characters, along with representations for alert, backspace, and carriage return. Run-time support for extended character sets has increased with each revision of the C standard.

Reserved words [edit]

C89 has 32 reserved words, as well known as keywords, which are the words that cannot be used for any purposes other than those for which they are predefined:

• motorcar
• break
• instance
• char
• const
• proceed
• default
• do
• double
• else
• enum
• extern
• bladder
• for
• goto
• if
• int
• long
• register
• return
• short
• signed
• sizeof
• static
• struct
• switch
• typedef
• spousal relationship
• unsigned
• void
• volatile
• while

C99 reserved v more than words:

• _Bool
• _Complex
• _Imaginary
• inline
• restrict

C11 reserved seven more words:^[26]

• _Alignas
• _Alignof
• _Atomic
• _Generic
• _Noreturn
• _Static_assert
• _Thread_local

Most of the recently reserved words brainstorm with an underscore followed by a uppercase, because identifiers of that form were previously reserved by the C standard for utilise just by implementations. Since existing program source code should non have been using these identifiers, it would non exist affected when C implementations started supporting these extensions to the programming linguistic communication. Some standard headers practice define more user-friendly synonyms for underscored identifiers. The language previously included a reserved word called entry, but this was seldom implemented, and has at present been removed as a reserved word.^[27]

Operators [edit]

C supports a rich set of operators, which are symbols used within an expression to specify the manipulations to exist performed while evaluating that expression. C has operators for:

• arithmetics: +, -, *, /, %
• assignment: =
• augmented consignment: +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=
• bitwise logic: ~, &, |, ^
• bitwise shifts: <<, >>
• boolean logic: !, &&, ||
• conditional evaluation: ? :
• equality testing: ==, !=
• calling functions: ( )
• increase and decrement: ++, --
• member option: ., ->
• object size: sizeof
• order relations: <, <=, >, >=
• reference and dereference: &, *, [ ]
• sequencing: ,
• subexpression grouping: ( )
• type conversion: (typename)

C uses the operator = (used in mathematics to limited equality) to bespeak consignment, post-obit the precedent of Fortran and PL/I, only different ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these two operators (assignment and equality) may event in the accidental utilise of one in place of the other, and in many cases, the error does non produce an error bulletin (although some compilers produce warnings). For example, the conditional expression if (a == b + 1) might mistakenly exist written equally if (a = b + 1), which will be evaluated as true if a is not zip after the assignment.^[28]

The C operator precedence is non ever intuitive. For example, the operator == binds more than tightly than (is executed prior to) the operators & (bitwise AND) and | (bitwise OR) in expressions such as 10 & one == 0, which must exist written as (x & 1) == 0 if that is the coder's intent.^[29]

"Hello, world" example [edit]

The "hello, world" case, which appeared in the first edition of K&R, has become the model for an introductory plan in most programming textbooks. The program prints "hullo, world" to the standard output, which is unremarkably a terminal or screen display.

The original version was:^[thirty]

                        main            ()                        {                                                printf            (            "hi, earth            \n            "            );                        }                      

A standard-conforming "hello, earth" programme is:^[a]

                        #include                                    <stdio.h>                        int                                    main            (            void            )                        {                                                printf            (            "hello, world            \n            "            );                        }                      

The outset line of the program contains a preprocessing directive, indicated by #include. This causes the compiler to supercede that line with the entire text of the stdio.h standard header, which contains declarations for standard input and output functions such as printf and scanf. The bending brackets surrounding stdio.h indicate that stdio.h is located using a search strategy that prefers headers provided with the compiler to other headers having the same name, as opposed to double quotes which typically include local or project-specific header files.

The next line indicates that a function named main is being defined. The main office serves a special purpose in C programs; the run-time environment calls the main function to begin programme execution. The blazon specifier int indicates that the value that is returned to the invoker (in this example the run-time environment) every bit a result of evaluating the main function, is an integer. The keyword void every bit a parameter listing indicates that this part takes no arguments.^[b]

The opening curly brace indicates the showtime of the definition of the chief function.

The side by side line calls (diverts execution to) a role named printf, which in this case is supplied from a arrangement 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, globe\north". The string literal is an unnamed array with elements of type char, prepare upwardly automatically by the compiler with a final 0-valued character to mark the end of the assortment (printf needs to know this). The \n is an escape sequence that C translates to a newline graphic symbol, 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 non used. (A more careful program might test the return value to decide whether or not the printf function succeeded.) The semicolon ; terminates the argument.

The closing curly brace indicates the cease of the code for the main function. According to the C99 specification and newer, the chief office, different whatsoever other office, will implicitly render a value of 0 upon reaching the } that terminates the office. (Formerly an explicit return 0; statement was required.) This is interpreted by the run-time arrangement equally an go out lawmaking indicating successful execution.^[31]

Data types [edit]

The type system in C is static and weakly typed, which makes information technology like to the type system of ALGOL descendants such as Pascal.^[32] At that place are built-in types for integers of various sizes, both signed and unsigned, floating-signal numbers, and enumerated types (enum). Integer blazon char is often used for single-byte characters. C99 added a boolean datatype. There are also derived types including arrays, pointers, records (struct), and unions (union).

C is frequently 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 tin override the checks in various means, either by using a blazon bandage to explicitly convert a value from one type to another, or past using pointers or unions to reinterpret the underlying $.25 of a data object in some other manner.

Some find C'due south declaration syntax unintuitive, particularly for function pointers. (Ritchie'southward idea was to declare identifiers in contexts resembling their use: "declaration reflects use".)^[33]

C's usual arithmetic conversions allow for efficient lawmaking to be generated, but can sometimes produce unexpected results. For example, a comparison of signed and unsigned integers of equal width requires a conversion of the signed value to unsigned. This can generate unexpected results if the signed value is negative.

Pointers [edit]

C supports the employ of pointers, a type of reference that records the address or location of an object or function in retentiveness. Pointers can exist dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can exist manipulated using assignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-within-give-and-take field), but since a pointer's type includes the type of the thing pointed to, expressions including pointers can exist blazon-checked at compile time. Pointer arithmetics is automatically scaled by the size of the pointed-to information type. Pointers are used for many purposes in C. Text strings are normally manipulated using pointers into arrays of characters. Dynamic memory allocation is performed using pointers. Many data types, such equally copse, are normally implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to higher-order functions (such as qsort or bsearch) or as callbacks to exist invoked by event handlers.^[31]

A nada pointer value explicitly points to no valid location. Dereferencing a zilch pointer value is undefined, often resulting in a segmentation fault. Nix arrow values 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 appropriate contexts in source code, such every bit for assigning to a pointer variable, a aught pointer abiding tin be written as 0, with or without explicit casting to a pointer type, or as the NULL macro defined past several standard headers. In conditional contexts, null pointer values evaluate to false, while all other pointer values evaluate to true.

Void pointers (void *) point to objects of unspecified type, and tin can therefore be used as "generic" data pointers. Since the size and type of the pointed-to object is not known, void pointers cannot exist dereferenced, nor is pointer arithmetics on them allowed, although they can easily be (and in many contexts implicitly are) converted to and from whatever other object pointer type.^[31]

Careless use of pointers is potentially unsafe. Because they are typically unchecked, a pointer variable tin be made to betoken to any arbitrary location, which can cause undesirable furnishings. Although properly used pointers point to safe places, they can be made to bespeak to unsafe places by using invalid arrow arithmetic; the objects they signal to may go on to be used later on deallocation (dangling pointers); they may exist used without having been initialized (wild pointers); or they may be straight assigned an dangerous value using a cast, spousal relationship, 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 diverse levels of checking. Some other programming languages address these problems past using more restrictive reference types.

Arrays [edit]

Assortment types in C are traditionally of a stock-still, static size specified at compile time. The more recent C99 standard also allows a course of variable-length arrays. However, it is besides possible to allocate a cake of retentivity (of arbitrary size) at run-fourth dimension, using the standard library's malloc role, and treat it equally an array.

Since arrays are e'er accessed (in effect) via pointers, array accesses are typically not checked against the underlying array size, although some compilers may provide premises checking as an option.^{[34] [35]} Array bounds violations are therefore possible and can atomic number 82 to various repercussions, including illegal memory accesses, corruption of data, buffer overruns, and run-fourth dimension exceptions.

C does non have a special provision for declaring multi-dimensional arrays, but rather relies on recursion within the blazon system to declare arrays of arrays, which effectively accomplishes the aforementioned thing. The index values of the resulting "multi-dimensional array" tin can exist thought of as increasing in row-major order. Multi-dimensional arrays are normally used in numerical algorithms (mainly from applied linear algebra) to store matrices. The construction of the C array is well suited to this particular task. However, in early on versions of C 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 exist accessed using double indexing. (A workaround for this was to allocate the array with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this issue.

The following example using mod C (C99 or after) shows allocation of a two-dimensional array on the heap and the use of multi-dimensional array indexing for accesses (which tin can use bounds-checking on many C compilers):

                        int                                    func            (            int                                    North            ,                                    int                                    M            )                        {                                                float                                    (            *            p            )[            N            ][            M            ]                                    =                                    malloc            (            sizeof                                    *            p            );                                                if                                    (            !            p            )                                                render                                    -ane            ;                                                for                                    (            int                                    i                                    =                                    0            ;                                    i                                    <                                    Due north            ;                                    i            ++            )                                                for                                    (            int                                    j                                    =                                    0            ;                                    j                                    <                                    Thou            ;                                    j            ++            )                                                (            *            p            )[            i            ][            j            ]                                    =                                    i                                    +                                    j            ;                                                print_array            (            N            ,                                    M            ,                                    p            );                                                gratis            (            p            );                                                return                                    1            ;                        }                      

Array–pointer interchangeability [edit]

The subscript note x[i] (where x designates a pointer) is syntactic sugar for *(10+i).^[36] Taking advantage of the compiler's knowledge of the pointer type, the address that x + i points to is not the base of operations address (pointed to past x) incremented by i bytes, but rather is defined to exist the base address incremented by i multiplied by the size of an chemical element that x points to. Thus, ten[i] designates the i+1th element of the array.

Furthermore, in most expression contexts (a notable exception is as operand of sizeof), an expression of array type is automatically converted to a pointer to the array's outset element. This implies that an array is never copied as a whole when named equally an statement to a function, only rather only the address of its showtime chemical element is passed. Therefore, although function calls in C use pass-by-value semantics, arrays are in effect passed by reference.

The full size of an array x can be determined by applying sizeof to an expression of array type. The size of an element can be determined by applying the operator sizeof to whatever dereferenced element of an array A, as in n = sizeof A[0]. This, the number of elements in a declared array A can exist determined as sizeof A / sizeof A[0]. Annotation, that if only a pointer to the outset element is bachelor as information technology is often the case in C lawmaking considering of the automatic conversion described above, the data most the full blazon of the array and its length are lost.

Memory management [edit]

One of the most of import functions of a programming linguistic communication is to provide facilities for managing memory and the objects that are stored in memory. C provides three distinct ways to allocate retention for objects:^[31]

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

These 3 approaches are appropriate in different situations and have various merchandise-offs. For example, static retentiveness resource allotment has little allotment overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially have a neat deal of overhead for both allotment and deallocation. The persistent nature of static objects is useful for maintaining state data across function calls, automatic allocation is easy to use merely stack space is typically much more express and transient than either static memory or heap space, and dynamic memory allocation allows user-friendly allocation of objects whose size is known only at run-fourth dimension. Most C programs make extensive use of all three.

Where possible, automatic or static allotment is usually simplest because the storage is managed past the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. However, many data structures tin change in size at runtime, and since static allocations (and automatic allocations before C99) must have a fixed size at compile-time, there are many situations in which dynamic allocation is necessary.^[31] Prior to the C99 standard, variable-sized arrays were a common case of this. (See the article on malloc for an example of dynamically allocated arrays.) Different automatic resource allotment, which can fail at run time with uncontrolled consequences, the dynamic resource allotment functions render an indication (in the form of a null pointer value) when the required storage cannot be allocated. (Static allocation that is besides big is usually detected by the linker or loader, earlier the plan can even begin execution.)

Unless otherwise specified, static objects contain zero or null arrow values upon plan startup. Automatically and dynamically allocated objects are initialized merely if an initial value is explicitly specified; otherwise they initially have indeterminate values (typically, whatsoever bit pattern happens to be present in the storage, which might not fifty-fifty represent a valid value for that type). If the program attempts to access an uninitialized value, the results are undefined. Many modern compilers try to find and warn about this problem, but both imitation positives and false negatives can occur.

Heap memory allocation has to be synchronized with its actual usage in any program to be reused as much every bit possible. For instance, if the merely pointer to a heap retention allotment goes out of telescopic or has its value overwritten before it is deallocated explicitly, then that retentivity cannot exist recovered for subsequently reuse and is essentially lost to the program, a phenomenon known as a memory leak. Conversely, it is possible for memory to be freed, but is referenced subsequently, leading to unpredictable results. Typically, the failure symptoms appear in a portion of the program unrelated to the lawmaking that causes the mistake, making it difficult to diagnose the failure. Such issues are ameliorated in languages with automatic garbage collection.

Libraries [edit]

The C programming linguistic communication uses libraries as its primary method of extension. In C, a library is a fix of functions contained within a single "annal" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used past a plan, 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 (east.m., -lm, shorthand for "link the math library").^[31]

The most mutual C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation (implementations which target express environments such as embedded systems may provide but a subset of the standard library). This library supports stream input and output, memory allocation, mathematics, character strings, and time values. Several separate standard headers (for instance, stdio.h) specify the interfaces for these and other standard library facilities.

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.

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 so create interfaces to the library and then that the routines can exist used from higher-level languages like Coffee, Perl, and Python.^[31]

File treatment and streams [edit]

File input and output (I/O) is not part of the C language itself just instead is handled by libraries (such as the C standard library) and their associated header files (e.g. stdio.h). File treatment is by and large implemented through high-level I/O which works through streams. A stream is from this perspective a data flow that is independent of devices, while a file is a concrete device. The loftier-level I/O is done through the clan of a stream to a file. In the C standard library, a buffer (a retention expanse or queue) is temporarily used to store data before it'due south sent to the final destination. This reduces the fourth dimension spent waiting for slower devices, for case a difficult drive or solid land bulldoze. Depression-level I/O functions are not role of the standard C library^{[ clarification needed ]} only are generally part of "bare metal" programming (programming that's independent of any operating system such equally almost embedded programming). With few exceptions, implementations include low-level I/O.

Language tools [edit]

A number of tools take been developed to help C programmers find and prepare statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided by the compiler. The tool lint was the first such, leading to many others.

Automated source code checking and auditing are beneficial in any language, and for C many such tools be, such every bit Lint. A common practice is to utilize Lint to detect questionable code when a program is commencement written. Once a program passes Lint, information technology is and then compiled using the C compiler. Also, many compilers can optionally warn most syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary set up of guidelines to avoid such questionable code, developed for embedded systems.^[37]

There are also compilers, libraries, and operating organisation level mechanisms for performing actions that are not a standard role of C, such as premises checking for arrays, detection of buffer overflow, serialization, dynamic memory tracking, and automated garbage drove.

Tools such as Purify or Valgrind and linking with libraries containing special versions of the memory allocation functions can assistance uncover runtime errors in retention usage.

Uses [edit]

The C Programming Linguistic communication

C is widely used for systems programming in implementing operating systems and embedded organisation applications,^[38] considering C code, when written for portability, can be used for most purposes, yet when needed, organization-specific code can exist used to admission specific hardware addresses and to perform type punning to match externally imposed interface requirements, with a low run-fourth dimension demand on organisation resources.

C tin can exist used for website programming using the Mutual Gateway Interface (CGI) as a "gateway" for information between the Web application, the server, and the browser.^[39] C is oftentimes chosen over interpreted languages because of its speed, stability, and near-universal availability.^[40]

A upshot of C'south wide availability and efficiency is that compilers, libraries and interpreters of other programming languages are often implemented in C. For instance, the reference implementations of Python, Perl, Ruby-red, and PHP are written in C.

C enables programmers to create efficient implementations of algorithms and data structures, because the layer of abstraction from hardware is sparse, and its overhead is depression, an important criterion for computationally intensive programs. For example, the GNU Multiple Precision Arithmetic Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.

C is sometimes used as an intermediate language past implementations of other languages. This arroyo may exist used for portability or convenience; by using C as an intermediate language, additional auto-specific code generators are not necessary. C has some features, such as line-number preprocessor directives and optional superfluous commas at the end of initializer lists, that support compilation of generated lawmaking. Yet, some of C'due south shortcomings have prompted the development of other C-based languages specifically designed for use as intermediate languages, such as C--.

C has also been widely used to implement end-user applications. Yet, such applications can too be written in newer, higher-level languages.

[edit]

The TIOBE index graph, showing a comparison of the popularity of various programming languages^[41]

C has both directly and indirectly influenced many later languages such as C#, D, Get, Coffee, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix's C shell.^[42] 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, information models, and/or big-scale program structures that differ from those of C, sometimes radically.

Several C or near-C interpreters exist, including Ch and CINT, which can besides be used for scripting.

When object-oriented programming languages became pop, C++ and Objective-C were two different extensions of C that provided object-oriented capabilities. Both languages were originally implemented as source-to-source compilers; source code was translated into C, and so compiled with a C compiler.^[43]

The C++ programming language (originally named "C with Classes") was devised by Bjarne Stroustrup equally an approach to providing object-oriented functionality with a C-like syntax.^[44] C++ adds greater typing force, 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.

Objective-C was originally a very "thin" layer on top of C, and remains a strict superset of C that permits object-oriented programming using a hybrid dynamic/static typing epitome. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, role declarations, and office calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk.

In addition to C++ and Objective-C, Ch, Cilk, and Unified Parallel C are nearly supersets of C.

See as well [edit]

• Compatibility of C and C++
• Comparison of Pascal and C
• Comparing of programming languages
• International Obfuscated C Lawmaking Contest
• List of C-based programming languages
• List of C compilers

Notes [edit]

1. ^ The original instance code volition compile on most modern compilers that are not in strict standard compliance mode, simply information technology does non fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic message be produced.
2. ^ The main office really has ii arguments, int argc and char *argv[], respectively, which tin exist used to handle control line arguments. The ISO C standard (section 5.1.two.2.1) requires both forms of principal to be supported, which is special handling not afforded to whatever other part.

References [edit]

1. ^ ^{a b} Kernighan, Brian Westward.; Ritchie, Dennis M. (February 1978). The C Programming Linguistic communication (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110163-0.
2. ^ Ritchie (1993): "Thompson had made a brief attempt to produce a system coded in an early on version of C—before structures—in 1972, but gave up the effort."
3. ^ Fruderica (December xiii, 2020). "History of C". The cppreference.com. Archived from the original on October 24, 2020. Retrieved October 24, 2020.
4. ^ Ritchie (1993): "The scheme of type limerick adopted by C owes considerable debt to Algol 68, although it did not, perhaps, emerge in a form that Algol's adherents would corroborate of."
5. ^ Ring Team (October 23, 2021). "The Ring programming language and other languages". ring-lang.net.
6. ^ ^{a b} "Verilog HDL (and C)" (PDF). The Research School of Informatics at the Australian National University. June three, 2010. Archived from the original (PDF) on November half-dozen, 2013. Retrieved Baronial 19, 2013. 1980s: ; Verilog outset introduced ; Verilog inspired by the C programming language
7. ^ ^{a b c d e} Ritchie (1993)
8. ^ "Programming Language Popularity". 2009. Archived from the original on Jan sixteen, 2009. Retrieved January sixteen, 2009.
9. ^ "TIOBE Programming Customs Alphabetize". 2009. Archived from the original on May 4, 2009. Retrieved May 6, 2009.
10. ^ ^{a b} "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
11. ^ "TIOBE Index for October 2021". Retrieved October vii, 2021.
12. ^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on Dec 12, 2019. Retrieved September 10, 2019.
13. ^ ^{a b} Johnson, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX Organization". Bell System Tech. J. 57 (6): 2021–2048. CiteSeerX10.i.one.138.35. doi:10.1002/j.1538-7305.1978.tb02141.x. S2CID 17510065. (Note: The PDF is an OCR browse of the original, and contains a rendering of "IBM 370" as "IBM 310".)
14. ^ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical written report). CSTR. Bell Labs. p. 10. 139. Archived (PDF) from the original on November xi, 2017. Retrieved February 1, 2015.
15. ^ "C manual pages". FreeBSD Miscellaneous Information Manual (FreeBSD 13.0 ed.). May 30, 2011. Archived from the original on Jan 21, 2021. Retrieved January 15, 2021. [1] Archived January 21, 2021, at the Wayback Machine
16. ^ Kernighan, Brian W.; Ritchie, Dennis Grand. (March 1988). The C Programming Language (2nd ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-thirteen-110362-7.
17. ^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Study). AT&T Labs. Archived (PDF) from the original on Baronial 24, 2014. Retrieved April xiv, 2014.
18. ^ C Integrity. International Organization for Standardization. March 30, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
19. ^ "JTC1/SC22/WG14 – C". Home page. ISO/IEC. Archived from the original on February 12, 2018. Retrieved June two, 2011.
20. ^ Andrew Binstock (October 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on August 2, 2013. Retrieved September vii, 2013.
21. ^ "Revised C23 Schedule WG 14 N 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October 10, 2021.
22. ^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on Feb 25, 2021. Retrieved July 26, 2011.
23. ^ Harbison, Samuel P.; Steele, Guy 50. (2002). C: A Reference Transmission (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-thirteen-089592-9. Contains a BNF grammar for C.
24. ^ Kernighan & Ritchie (1996), p. 192.
25. ^ Kernighan & Ritchie (1978), p. three.
26. ^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on December 22, 2017. Retrieved September 16, 2011.
27. ^ Kernighan & Ritchie (1996), pp. 192, 259.
28. ^ "x Common Programming Mistakes in C++". Cs.ucr.edu. Archived from the original on Oct 21, 2008. Retrieved June 26, 2009.
29. ^ Schultz, Thomas (2004). C and the 8051 (tertiary ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-1-58961-237-2. Archived from the original on July 29, 2020. Retrieved February 10, 2012.
30. ^ Kernighan & Ritchie (1978), p. half-dozen.
31. ^ ^{a b c d due east f g} Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-1-4493-2714-nine.
32. ^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparison of the Programming Languages C and Pascal". ACM Computing Surveys. 14 (1): 73–92. doi:10.1145/356869.356872. S2CID 3136859.
33. ^ Kernighan & Ritchie (1996), p. 122.
34. ^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January seven, 2007. Retrieved August five, 2012.
35. ^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-Instruction PUBLIC Company LIMITED. pp. 225–230. ISBN978-616-08-2740-4.
36. ^ Raymond, Eric S. (October 11, 1996). The New Hacker'southward Dictionary (tertiary ed.). MIT Press. p. 432. ISBN978-0-262-68092-9. Archived from the original on November 12, 2012. Retrieved August 5, 2012.
37. ^ "Man Page for lint (freebsd Department i)". unix.com. May 24, 2001. Retrieved July 15, 2014.
38. ^ Dale, Nell B.; Weems, Chip (2014). Programming and problem solving with C++ (6th ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
39. ^ Dr. Dobb's Sourcebook. United states of americaA.: Miller Freeman, Inc. November–December 1995.
40. ^ "Using C for CGI Programming". linuxjournal.com. March i, 2005. Archived from the original on February 13, 2010. Retrieved January iv, 2010.
41. ^ McMillan, Robert (August 1, 2013). "Is Java Losing Its Mojo?". Wired. Archived from the original on Feb 15, 2017. Retrieved March 5, 2017.
42. ^ O'Regan, Gerard (September 24, 2015). Pillars of computing : a compendium of select, pivotal applied science firms. ISBN978-3319214641. OCLC 922324121.
43. ^ Rauchwerger, Lawrence (2004). Languages and compilers for parallel computing : 16th international workshop, LCPC 2003, College Station, TX, USA, October 2-four, 2003 : revised papers. Springer. ISBN978-3540246442. OCLC 57965544.
44. ^ Stroustrup, Bjarne (1993). "A History of C++: 1979−1991" (PDF). Archived (PDF) from the original on February 2, 2019. Retrieved June 9, 2011.

Sources [edit]

• Ritchie, Dennis M. (March 1993). "The Development of the C Linguistic communication". ACM SIGPLAN Notices. ACM. 28 (three): 201–208. doi:ten.1145/155360.155580.
  Ritchie, Dennis Thou. (1993). "The Evolution of the C Language". The 2d ACM SIGPLAN Briefing on History of Programming Languages (HOPL-2). ACM. pp. 201–208. doi:x.1145/154766.155580. ISBN0-89791-570-4 . Retrieved November iv, 2014.
• Kernighan, Brian W.; Ritchie, Dennis G. (1996). The C Programming Language (2nd ed.). Prentice Hall. ISBN7-302-02412-X.

Farther reading [edit]

• Kernighan, Brian; Ritchie, Dennis (1988). The C Programming Linguistic communication (2 ed.). Prentice Hall. ISBN978-0131103627. (archive)
• Plauger, P.J. (1992). The Standard C Library (1 ed.). Prentice Hall. ISBN978-0131315099. (source)
• Banahan, 1000.; Brady, D.; Doran, 1000. (1991). The C Book: Featuring the ANSI C Standard (two ed.). Addison-Wesley. ISBN978-0201544336. (free)
• Harbison, Samuel; Steele Jr, Guy (2002). C: A Reference Manual (5 ed.). Pearson. ISBN978-0130895929. (annal)
• Male monarch, Thousand.N. (2008). C Programming: A Modern Approach (2 ed.). W. W. Norton. ISBN978-0393979503. (archive)
• Griffiths, David; Griffiths, Dawn (2012). Head First C (1 ed.). O'Reilly. ISBN978-1449399917.
• Perry, Greg; Miller, Dean (2013). C Programming: Absolute Beginner's Guide (3 ed.). Que. ISBN978-0789751980.
• Deitel, Paul; Deitel, Harvey (2015). C: How to Program (8 ed.). Pearson. ISBN978-0133976892.
• Gustedt, Jens (2019). Modernistic C (2 ed.). Manning. ISBN978-1617295812. (free)

External links [edit]

• ISO C Working Group official website
  • ISO/IEC 9899, publicly available official C documents, including the C99 Rationale
  • "C99 with Technical corrigenda TC1, TC2, and TC3 included" (PDF). (three.61 MB)
• comp.lang.c Frequently Asked Questions
• A History of C, by Dennis Ritchie

smithnonon1972.blogspot.com

Source: https://en.wikipedia.org/wiki/C_(programming_language)