C# "the Support for the Specified Socket Type Does Not Exist in This Address Family"

Full general-purpose programming linguistic communication

C
Major implementations
The C Programming Language ^[1] (oftentimes referred to equally K&R), the seminal volume on C
Paradigm	Multi-paradigm: 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; 50 years ago (1972) ^[2]

Stable release	C17 / June 2018; 3 years ago (2018-06)
Preview release	C2x (N2731) / October 18, 2021; 4 months ago (2021-ten-18) ^[3]

Typing discipline	Static, weak, manifest, nominal
Os	Cross-platform
Filename extensions	.c, .h
Website	world wide web.iso.org/standard/74528.html www.open-std.org/jtc1/sc22/wg14/
pcc, GCC, Clang, Intel C, C++Builder, Microsoft Visual C++, Watcom C
Dialects
Whirlwind, Unified Parallel C, Split-C, Cilk, C*
Influenced by
B (BCPL, CPL), ALGOL 68,^[four] associates, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Get, 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 letterc) is a full general-purpose, procedural computer programming linguistic communication supporting structured programming, lexical variable scope, and recursion, with a static blazon system. By design, C provides constructs that map efficiently to typical machine instructions. It has found lasting use in applications previously coded in assembly language. Such applications include operating systems and various application software for computer architectures that range from supercomputers to PLCs and embedded systems.

A successor to the programming language B, C was originally adult at Bell Labs past Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system.^[7] During the 1980s, C gradually gained popularity. Information technology has become i of the most widely used programming languages,^[viii] ^[9] with C compilers from various vendors available for the bulk of existing computer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and past the International Organization for Standardization (ISO).

C is an imperative procedural language. It was designed to exist compiled to provide low-level access to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its low-level capabilities, the linguistic communication was designed to encourage cross-platform programming. A standards-compliant C program written with portability in mind can exist compiled for a wide multifariousness of computer platforms and operating systems with few changes to its source code.^[10]

Since 2000, C has consistently ranked amid the height 2 languages in the TIOBE alphabetize, a mensurate of the popularity of programming languages.^[11]

Overview

Like 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 contained inside subroutines (also chosen "functions", though not strictly in the sense of functional programming). Function parameters are always passed past value (except arrays). Pass-past-reference is false in C by explicitly passing pointer values. C program source text is gratuitous-format, using the semicolon as a argument terminator and curly braces for group blocks of statements.

The C linguistic communication besides exhibits the following characteristics:

The language has a small, stock-still number of keywords, including a full fix of control flow primitives: if/else, for, do/while, while, and switch. User-defined names are not distinguished from keywords by whatsoever kind of sigil.
It has a large number of arithmetics, bitwise, and logic operators: +,+=,++,&,||, etc.
More than one assignment may be performed in a single statement.
Functions:
- Office return values can be ignored, when not needed.
- Function and data pointers allow ad 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.
Announcement syntax mimics usage context. C has no "define" keyword; instead, a argument beginning with the name of a type is taken as a annunciation. In that location is no "function" keyword; instead, a function is indicated by the presence of a parenthesized argument list.
User-defined (typedef) and compound types are possible.
- Heterogeneous aggregate data types (struct) allow related data elements to exist accessed and assigned equally a unit of measurement.
- Union is a construction with overlapping members; only the last fellow member stored is valid.
- Array indexing is a secondary notation, divers in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects: they cannot be assigned or compared using single built-in operators. There is no "array" keyword in use or definition; instead, square brackets signal arrays syntactically, for example month[11].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are not a distinct data type, but are conventionally implemented as zero-terminated character arrays.
Low-level access to computer retentivity is possible past converting motorcar addresses to typed pointers.
Procedures (subroutines not returning values) are a special example of function, with an untyped return type void.
A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
There is a basic form of modularity: files tin can 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 equally I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does non include certain features found in other languages (such as object orientation and garbage drove), these can be implemented or emulated, oftentimes through the use of external libraries (e.m., the GLib Object Organisation or the Boehm garbage collector).

Relations to other languages

Many later languages have borrowed straight or indirectly from C, including C++, C#, Unix's C vanquish, D, Go, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[vi] These languages accept drawn many of their control structures and other basic features from C. Most of them (Python being a dramatic exception) as well express highly like syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, information models, and semantics that tin exist radically different.

History

Early on developments

Timeline of language development
Twelvemonth	C Standard^[10]
1972	Nascency
1978	K&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 system, originally implemented in associates linguistic communication on a PDP-7 past Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Eventually, they decided to port the operating organization to a PDP-11. The original PDP-11 version of Unix was also developed in assembly language.^[seven]

Thompson desired a programming linguistic communication to make utilities for the new platform. At first, he tried to brand a Fortran compiler, merely soon gave upwardly the idea. Instead, he created a cut-downward version of the recently developed BCPL systems programming linguistic communication. The official description of BCPL was not available at the fourth dimension,^[12] and Thompson modified the syntax to be less wordy, producing the like but somewhat simpler B.^[7] However, few utilities were ultimately written in B because it was as well slow, and B could not accept reward of PDP-xi features such as byte addressability.

In 1972, Ritchie started to amend B, virtually notably calculation information 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 iv Unix, released in November 1973, the Unix kernel was extensively re-implemented in C.^[vii] Past 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 also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I. Its original version provided merely included files and uncomplicated string replacements: #include and #define of parameterless macros. Soon afterward that, it was extended, mostly past Mike Lesk and then past John Reiser, to comprise macros with arguments and provisional compilation.^[7]

Unix was one of the kickoff operating system kernels implemented in a language other than assembly. Before instances include the Multics system (which was written in PL/I) and Primary Control Plan (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In around 1977, Ritchie and Stephen C. Johnson made farther 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.^[13]

K&R C

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Linguistic communication.^[ane] This book, known to C programmers every bit Grand&R, served for many years as an informal specification of the language. The version of C that information technology describes is commonly referred to every bit "K&R C". Every bit this was released in 1978, it is also referred to as C78.^[15] The 2nd edition of the book^[sixteen] covers the later ANSI C standard, described below.

K&R introduced several language features:

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

Even after the publication of the 1989 ANSI standard, for many years M&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 nonetheless in employ, and because carefully written K&R C code can exist legal Standard C as well.

In early versions of C, just functions that return types other than int must exist declared if used before the function definition; functions used without prior announcement were presumed to render 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            ();                                                render                                    test2            ;                        }

The int type specifiers which are commented out could exist omitted in 1000&R C, but are required in after standards.

Since K&R office declarations did non include whatever information well-nigh function arguments, function parameter type checks were not performed, although some compilers would issue a alarm message if a local office was called with the incorrect number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Separate tools such as Unix'southward lint utility were developed that (among other things) could check for consistency of function use across multiple source files.

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

void functions (i.eastward., functions with no return value)
functions returning struct or union types (rather than pointers)
assignment for struct data types
enumerated types

The big number of extensions and lack of understanding on a standard library, together with the linguistic communication popularity and the fact that not even the Unix compilers precisely implemented the Yard&R specification, led to the necessity of standardization.

ANSI C and ISO C

During the late 1970s and 1980s, versions of C were implemented for a wide variety of mainframe computers, minicomputers, and microcomputers, including the IBM PC, as its popularity began to increase significantly.

In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; still, the not-portable portion of the Unix C library was handed off to the IEEE working group 1003 to get the basis for the 1988 POSIX standard. In 1989, the C standard was ratified equally ANSI X3.159-1989 "Programming Linguistic communication C". This version of the linguistic communication is often referred to equally 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) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language.

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

One of the aims of the C standardization process was to produce a superset of M&R C, incorporating many of the afterward introduced unofficial features. The standards committee as well included several additional features such as function prototypes (borrowed from C++), void pointers, support for international graphic symbol sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the fashion used in C++, the K&R interface continued to be permitted, for compatibility with existing source code.

C89 is supported past current C compilers, and most mod C lawmaking is based on it. Any program written only in Standard C and without whatsoever hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile but on a sure platform or with a item compiler, due, for example, to the employ of not-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such every bit the exact size of information types and byte endianness.

In cases where code must be compilable by either standard-befitting or K&R C-based compilers, the __STDC__ macro can be used to carve up the code into Standard and K&R sections to prevent the utilize on a Grand&R C-based compiler of features bachelor simply in Standard C.

After the ANSI/ISO standardization procedure, 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 every bit C95) was published, to right some details and to add more extensive support for international graphic symbol sets.^[18]

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 equally "C99". It has since been amended iii times by Technical Corrigenda.^[19]

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

C99 is for the nigh function astern compatible with C90, simply is stricter in some ways; in particular, a proclamation 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 back up 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++eleven.^[20] ^{[ needs update ]}

In addition, support for Unicode identifiers (variable / function names) in the class of escaped characters (e.1000. \U0001f431) is now required. Support for raw Unicode names is optional.

C11

In 2007, work began on some other revision of the C standard, informally called "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 past existing implementations.

The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode back up, atomic operations, multi-threading, and bounds-checked functions. It 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 support is available.

C17

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

C2x

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

Embedded C

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

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

Syntax

C has a formal grammar specified by the C standard.^[23] Line endings are more often than not not significant in C; even so, line boundaries do have significance during the preprocessing stage. Comments may appear either between the delimiters /* and */, or (since C99) following // until the stop of the line. Comments delimited by /* and */ practice not nest, and these sequences of characters are non interpreted every bit annotate delimiters if they announced inside cord or character literals.^[24]

C source files contain declarations and role 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 perchance reserve storage for new variables, unremarkably past writing the type followed past the variable name. Keywords such as char and int specify built-in types. Sections of lawmaking are enclosed in braces ({ and }, sometimes called "curly brackets") to limit the telescopic of declarations and to human action equally a single argument for control structures.

As an imperative language, C uses statements to specify actions. The almost common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; equally a side effect of the evaluation, functions may be chosen and variables may exist assigned new values. To change the normal sequential execution of statements, C provides several control-catamenia statements identified by reserved keywords. Structured programming is supported by if … [else] conditional execution and by do … while, while, and for iterative execution (looping). The for argument has separate initialization, testing, and reinitialization expressions, any or all of which tin be omitted. break and go on tin be used to leave the innermost enclosing loop statement or skip to its reinitialization. There is as well a not-structured goto statement which branches directly to the designated label within the function. switch selects a instance to be executed based on the value of an integer expression.

Expressions can use a variety of built-in operators and may incorporate function calls. The gild in which arguments to functions and operands to almost operators are evaluated is unspecified. The evaluations may fifty-fifty be interleaved. Still, all side effects (including storage to variables) will occur before the adjacent "sequence point"; sequence points include the stop of each expression statement, and the entry to and return from each part call. Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a loftier degree of object code optimization by the compiler, simply 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 incorrect precedence; some parts of the syntax could exist better."^[25] The C standard did not attempt to right many of these blemishes, because of the impact of such changes on already existing software.

Graphic symbol set

The basic C source grapheme fix 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: infinite, horizontal tab, vertical tab, grade feed, newline

Newline indicates the end of a text line; information technology need not correspond to an bodily single character, although for convenience C treats it equally ane.

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

The basic C execution graphic symbol set up contains the aforementioned characters, along with representations for alert, backspace, and carriage render. Run-fourth dimension support for extended character sets has increased with each revision of the C standard.

Reserved words

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

auto
break
case
char
const
continue
default
practise
double
else
enum
extern
float
for
goto
if
int
long
register
return
short
signed
sizeof
static
struct
switch
typedef
matrimony
unsigned
void
volatile
while

C99 reserved v more words:

_Bool
_Complex
_Imaginary
inline
restrict

C11 reserved seven more words:^[26]

_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert
_Thread_local

Near of the recently reserved words begin with an underscore followed by a majuscule alphabetic character, because identifiers of that grade were previously reserved by the C standard for use only by implementations. Since existing programme source code should non have been using these identifiers, it would not be afflicted when C implementations started supporting these extensions to the programming linguistic communication. Some standard headers do ascertain more user-friendly synonyms for underscored identifiers. The language previously included a reserved word called entry, merely this was seldom implemented, and has at present been removed as a reserved word.^[27]

Operators

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

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

C uses the operator = (used in mathematics to express equality) to indicate assignment, following the precedent of Fortran and PL/I, just unlike ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these two operators (consignment and equality) may result in the accidental use of one in place of the other, and in many cases, the fault does not produce an error bulletin (although some compilers produce warnings). For instance, the provisional expression if (a == b + one) might mistakenly exist written equally if (a = b + 1), which will be evaluated as truthful if a is not zero later on the consignment.^[28]

The C operator precedence is not ever intuitive. For example, the operator == binds more tightly than (is executed prior to) the operators & (bitwise AND) and | (bitwise OR) in expressions such as x & ane == 0, which must exist written as (x & 1) == 0 if that is the coder'southward intent.^[29]

"How-do-you-do, world" instance

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

The original version was:^[30]

                        principal            ()                        {                                                printf            (            "hello, world            \n            "            );                        }

A standard-conforming "hullo, world" program is:^[a]

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

The start line of the program contains a preprocessing directive, indicated by #include. This causes the compiler to supplant 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 proper name, every bit opposed to double quotes which typically include local or projection-specific header files.

The next line indicates that a function named chief is existence defined. The master function serves a special purpose in C programs; the run-fourth dimension environment calls the principal function to begin program execution. The blazon specifier int indicates that the value that is returned to the invoker (in this case the run-time surround) as a outcome of evaluating the principal function, is an integer. The keyword void as a parameter listing indicates that this office takes no arguments.^[b]

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

The next line calls (diverts execution to) a function named printf, which in this case is supplied from a organization library. In this phone call, the printf function is passed (provided with) a single argument, the accost of the first character in the string literal "howdy, earth\n". The string literal is an unnamed array with elements of type char, set up upward automatically by the compiler with a terminal 0-valued character to marking the end of the array (printf needs to know this). The \northward is an escape sequence that C translates to a newline character, which on output signifies the end of the electric current line. The render value of the printf function is of type int, simply it is silently discarded since it is not used. (A more careful plan might test the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement.

The closing curly brace indicates the end of the code for the main role. According to the C99 specification and newer, the master function, unlike any other function, will implicitly return a value of 0 upon reaching the } that terminates the function. (Formerly an explicit return 0; statement was required.) This is interpreted by the run-time system equally an leave code indicating successful execution.^[31]

Data types

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

C is often used in depression-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure type definiteness of most expressions, merely the programmer can override the checks in diverse ways, either by using a type bandage to explicitly convert a value from i type to another, or by using pointers or unions to reinterpret the underlying bits of a data object in another mode.

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

C's usual arithmetic conversions permit for efficient lawmaking to be generated, but can sometimes produce unexpected results. For case, 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

C supports the use of pointers, a blazon of reference that records the accost or location of an object or role in retentivity. Pointers tin can exist dereferenced to admission data stored at the accost pointed to, or to invoke a pointed-to function. Pointers can exist manipulated using consignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-inside-word field), but since a pointer's blazon includes the type of the thing pointed to, expressions including pointers can exist type-checked at compile time. Pointer arithmetics is automatically scaled by the size of the pointed-to data type. Pointers are used for many purposes in C. Text strings are ordinarily manipulated using pointers into arrays of characters. Dynamic memory allocation is performed using pointers. Many data types, such as trees, are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to higher-club functions (such equally qsort or bsearch) or every bit callbacks to exist invoked by event handlers.^[31]

A null arrow value explicitly points to no valid location. Dereferencing a zippo pointer value is undefined, oft resulting in a sectionalization fault. Null pointer values are useful for indicating special cases such every bit 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 null arrow abiding tin be written as 0, with or without explicit casting to a pointer type, or equally the NULL macro defined by several standard headers. In conditional contexts, nix arrow values evaluate to false, while all other arrow values evaluate to truthful.

Void pointers (void *) point to objects of unspecified blazon, and tin can therefore be used as "generic" information 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 immune, although they can easily be (and in many contexts implicitly are) converted to and from any other object arrow blazon.^[31]

Careless utilise of pointers is potentially dangerous. Considering they are typically unchecked, a pointer variable can be fabricated to point to any arbitrary location, which can crusade undesirable furnishings. Although properly used pointers point to safety places, they tin can be made to point to dangerous places by using invalid pointer arithmetic; the objects they betoken to may continue to exist used after deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may be directly assigned an dangerous value using a cast, matrimony, or through another corrupt pointer. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more than restrictive reference types.

Arrays

Array types in C are traditionally of a stock-still, static size specified at compile time. The more contempo C99 standard also allows a form of variable-length arrays. Even so, information technology is likewise possible to allocate a block of memory (of arbitrary size) at run-fourth dimension, using the standard library'due south malloc office, and treat it every bit an array.

Since arrays are ever accessed (in result) via pointers, array accesses are typically not checked against the underlying assortment size, although some compilers may provide bounds checking every bit an pick.^[34] ^[35] Array bounds violations are therefore possible and can lead to various repercussions, including illegal retention accesses, corruption of data, buffer overruns, and run-time exceptions.

C does not have a special provision for declaring multi-dimensional 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 "multi-dimensional array" can be thought of as increasing in row-major lodge. Multi-dimensional arrays are usually used in numerical algorithms (mainly from applied linear algebra) to shop matrices. The structure of the C array is well suited to this particular job. Nonetheless, in early versions of C the bounds of the array must exist known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this was to allocate the array with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this consequence.

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

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

Array–pointer interchangeability

The subscript notation x[i] (where x designates a arrow) is syntactic sugar for *(ten+i).^[36] Taking advantage of the compiler's knowledge of the pointer type, the address that x + i points to is not the base address (pointed to by 10) incremented by i bytes, simply rather is defined to be the base address incremented by i multiplied past the size of an element that ten points to. Thus, 10[i] designates the i+aneth element of the assortment.

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

The full size of an array ten can be determined past applying sizeof to an expression of array type. The size of an element can be determined past applying the operator sizeof to whatever dereferenced element of an array A, every bit in n = sizeof A[0]. This, the number of elements in a declared array A tin be adamant as sizeof A / sizeof A[0]. Note, that if only a arrow to the outset element is bachelor as it is ofttimes the case in C code because of the automatic conversion described above, the information almost the full type of the array and its length are lost.

Memory management

Ane of the nearly important functions of a programming language is to provide facilities for managing retentivity and the objects that are stored in memory. C provides three distinct ways to allocate memory for objects:^[31]

Static retention allotment: 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 allotment: temporary objects can be stored on the stack, and this space is automatically freed and reusable afterward the cake in which they are declared is exited.
Dynamic retention allocation: blocks of memory of arbitrary size can be requested at run-time using library functions such as malloc from a region of retention called the heap; these blocks persist until subsequently freed for reuse by calling the library function realloc or free

These three approaches are appropriate in different situations and have various trade-offs. For example, static retentiveness allocation has little allocation overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially have a great deal of overhead for both resource allotment and deallocation. The persistent nature of static objects is useful for maintaining state information across function calls, automatic allocation is piece of cake to use but stack infinite is typically much more than limited and transient than either static memory or heap infinite, and dynamic memory allocation allows convenient resource allotment of objects whose size is known only at run-time. Nearly C programs make extensive use of all three.

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

Unless otherwise specified, static objects contain naught or zip pointer values upon program startup. Automatically and dynamically allocated objects are initialized only 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 non even correspond a valid value for that type). If the programme attempts to access an uninitialized value, the results are undefined. Many mod compilers attempt to detect and warn about this problem, but both false positives and false negatives tin can occur.

Heap retentivity allocation has to be synchronized with its actual usage in whatever program to be reused as much every bit possible. For example, if the only arrow to a heap memory allocation goes out of telescopic or has its value overwritten earlier it is deallocated explicitly, then that memory cannot be recovered for subsequently reuse and is essentially lost to the program, a phenomenon known as a retentiveness leak. Conversely, information technology is possible for retention 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 code that causes the error, making it hard to diagnose the failure. Such bug are ameliorated in languages with automatic garbage collection.

Libraries

The C programming language uses libraries as its primary method of extension. In C, a library is a prepare of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used past a program, and declarations of special data types and macro symbols used with these functions. In lodge for a program to use a library, it must include the library'due south header file, and the library must be linked with the program, which in many cases requires compiler flags (e.k., -lm, shorthand for "link the math library").^[31]

The most common C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation (implementations which target limited environments such as embedded systems may provide merely 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 example, stdio.h) specify the interfaces for these and other standard library facilities.

Some other mutual set of C library functions are those used past applications specifically targeted for Unix and Unix-similar 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, at that place are a broad variety of other libraries available. Libraries are often written in C because C compilers generate efficient object code; programmers then create interfaces to the library and then that the routines tin can exist used from higher-level languages like Java, Perl, and Python.^[31]

File handling and streams

File input and output (I/O) is non part of the C language itself simply instead is handled by libraries (such as the C standard library) and their associated header files (e.g. stdio.h). File handling is generally 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 association of a stream to a file. In the C standard library, a buffer (a memory area or queue) is temporarily used to store data before it's sent to the concluding destination. This reduces the time spent waiting for slower devices, for example a hard bulldoze or solid state drive. Low-level I/O functions are non function of the standard C library^{[ clarification needed ]} but are more often than not part of "blank metallic" programming (programming that'due south independent of any operating organization such as most embedded programming). With few exceptions, implementations include low-level I/O.

Language tools

A number of tools take been developed to help C programmers find and fix 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 lawmaking checking and auditing are beneficial in any language, and for C many such tools be, such as Lint. A common practice is to utilise Lint to detect questionable code when a program is first written. Once a program passes Lint, it is and then compiled using the C compiler. Likewise, many compilers can optionally warn about syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary set of guidelines to avoid such questionable code, developed for embedded systems.^[37]

There are too compilers, libraries, and operating system level mechanisms for performing actions that are not a standard function of C, such as bounds checking for arrays, detection of buffer overflow, serialization, dynamic retentivity tracking, and automatic garbage drove.

Tools such as Purify or Valgrind and linking with libraries containing special versions of the retentiveness resource allotment functions can assist uncover runtime errors in retentivity usage.

Uses

The C Programming Language

C is widely used for systems programming in implementing operating systems and embedded system applications,^[38] because C lawmaking, when written for portability, can be used for almost purposes, notwithstanding when needed, system-specific code can be used to access specific hardware addresses and to perform blazon punning to match externally imposed interface requirements, with a low run-time demand on system resource.

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

A outcome of C's broad 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, Scarlet, 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 thin, 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 by implementations of other languages. This arroyo may be used for portability or convenience; by using C as an intermediate linguistic communication, boosted automobile-specific code generators are non necessary. C has some features, such every bit line-number preprocessor directives and optional superfluous commas at the end of initializer lists, that back up compilation of generated lawmaking. However, some of C'due south shortcomings take prompted the development of other C-based languages specifically designed for apply equally intermediate languages, such every bit C--.

C has as well been widely used to implement finish-user applications. Nevertheless, such applications can also exist written in newer, higher-level languages.

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

C has both straight and indirectly influenced many after languages such equally C#, D, Go, 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 blazon systems, data models, and/or big-calibration program structures that differ from those of C, sometimes radically.

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

When object-oriented programming languages became popular, C++ and Objective-C were 2 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 and then compiled with a C compiler.^[43]

The C++ programming language (originally named "C with Classes") was devised by Bjarne Stroustrup as an approach to providing object-oriented functionality with a C-like syntax.^[44] C++ adds greater typing strength, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. About 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 image. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations, and part 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.

Notes

^ The original example code will compile on almost modern compilers that are not in strict standard compliance mode, merely it does not fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic message be produced.
^ The primary function really has two arguments, int argc and char *argv[], respectively, which can exist used to handle control line arguments. The ISO C standard (section v.one.two.2.1) requires both forms of master to exist supported, which is special treatment not afforded to whatsoever other function.

References

^ ^a ^b Kernighan, Brian W.; Ritchie, Dennis M. (February 1978). The C Programming Linguistic communication (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-xiii-110163-0.
^ Ritchie (1993): "Thompson had made a cursory endeavor to produce a system coded in an early on version of C—before structures—in 1972, but gave up the endeavour."
^ Fruderica (December 13, 2020). "History of C". The cppreference.com. Archived from the original on October 24, 2020. Retrieved October 24, 2020.
^ Ritchie (1993): "The scheme of type limerick adopted by C owes considerable debt to Algol 68, although it did not, perhaps, emerge in a course that Algol's adherents would approve of."
^ Ring Team (October 23, 2021). "The Ring programming language and other languages". ring-lang.cyberspace.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Research School of Information science at the Australian National University. June 3, 2010. Archived from the original (PDF) on November half-dozen, 2013. Retrieved Baronial 19, 2013. 1980s: ; Verilog beginning introduced ; Verilog inspired by the C programming language
^ ^a ^b ^c ^d ^e Ritchie (1993)
^ "Programming Language Popularity". 2009. Archived from the original on January sixteen, 2009. Retrieved January 16, 2009.
^ "TIOBE Programming Customs Alphabetize". 2009. Archived from the original on May 4, 2009. Retrieved May 6, 2009.
^ ^a ^b "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
^ "TIOBE Index for October 2021". Retrieved October 7, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on December 12, 2019. Retrieved September x, 2019.
^ ^a ^b Johnson, South. C.; Ritchie, D. G. (1978). "Portability of C Programs and the UNIX Organisation". Bell Arrangement Tech. J. 57 (6): 2021–2048. CiteSeerXx.1.1.138.35. doi:x.1002/j.1538-7305.1978.tb02141.ten. S2CID 17510065. (Note: The PDF is an OCR scan of the original, and contains a rendering of "IBM 370" as "IBM 310".)
^ McIlroy, K. D. (1987). A Research Unix reader: annotated excerpts from the Developer's Manual, 1971–1986 (PDF) (Technical study). CSTR. Bong Labs. p. x. 139. Archived (PDF) from the original on Nov xi, 2017. Retrieved February 1, 2015.
^ "C manual pages". FreeBSD Miscellaneous Information Transmission (FreeBSD 13.0 ed.). May xxx, 2011. Archived from the original on Jan 21, 2021. Retrieved Jan 15, 2021. [1] Archived January 21, 2021, at the Wayback Automobile
^ Kernighan, Brian W.; Ritchie, Dennis M. (March 1988). The C Programming Language (2nd ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110362-7.
^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Study). AT&T Labs. Archived (PDF) from the original on August 24, 2014. Retrieved April 14, 2014.
^ C Integrity. International Organisation for Standardization. March 30, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
^ "JTC1/SC22/WG14 – C". Dwelling page. ISO/IEC. Archived from the original on Feb 12, 2018. Retrieved June ii, 2011.
^ Andrew Binstock (October 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on Baronial 2, 2013. Retrieved September 7, 2013.
^ "Revised C23 Schedule WG 14 Northward 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October ten, 2021.
^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on February 25, 2021. Retrieved July 26, 2011.
^ Harbison, Samuel P.; Steele, Guy L. (2002). C: A Reference Manual (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-nine. Contains a BNF grammar for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. 3.
^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on December 22, 2017. Retrieved September 16, 2011.
^ Kernighan & Ritchie (1996), pp. 192, 259.
^ "ten Mutual Programming Mistakes in C++". Cs.ucr.edu. Archived from the original on Oct 21, 2008. Retrieved June 26, 2009.
^ Schultz, Thomas (2004). C and the 8051 (tertiary ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-i-58961-237-ii. Archived from the original on July 29, 2020. Retrieved Feb 10, 2012.
^ Kernighan & Ritchie (1978), p. vi.
^ ^a ^b ^c ^d ^e ^f ^g Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-1-4493-2714-nine.
^ 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.
^ Kernighan & Ritchie (1996), p. 122.
^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on Jan 7, 2007. Retrieved Baronial v, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-EDUCATION PUBLIC Visitor Limited. pp. 225–230. ISBN978-616-08-2740-four.
^ Raymond, Eric South. (October 11, 1996). The New Hacker's Lexicon (tertiary ed.). MIT Press. p. 432. ISBN978-0-262-68092-nine. Archived from the original on November 12, 2012. Retrieved August five, 2012.
^ "Human Folio for lint (freebsd Section 1)". unix.com. May 24, 2001. Retrieved July 15, 2014.
^ Dale, Nell B.; Weems, Bit (2014). Programming and problem solving with C++ (sixth ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
^ Dr. Dobb's Sourcebook. U.s.a.A.: Miller Freeman, Inc. November–December 1995.
^ "Using C for CGI Programming". linuxjournal.com. March 1, 2005. Archived from the original on February 13, 2010. Retrieved Jan four, 2010.
^ McMillan, Robert (Baronial 1, 2013). "Is Java Losing Its Mojo?". Wired. Archived from the original on February 15, 2017. Retrieved March 5, 2017.
^ O'Regan, Gerard (September 24, 2015). Pillars of computing : a compendium of select, pivotal technology firms. ISBN978-3319214641. OCLC 922324121.
^ 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.
^ Stroustrup, Bjarne (1993). "A History of C++: 1979−1991" (PDF). Archived (PDF) from the original on February 2, 2019. Retrieved June 9, 2011.

Sources

Ritchie, Dennis 1000. (March 1993). "The Development of the C Language". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:x.1145/155360.155580.
Ritchie, Dennis 1000. (1993). "The Evolution of the C Language". The Second ACM SIGPLAN Briefing on History of Programming Languages (HOPL-II). ACM. pp. 201–208. doi:10.1145/154766.155580. ISBN0-89791-570-4 . Retrieved November iv, 2014.
Kernighan, Brian Due west.; Ritchie, Dennis M. (1996). The C Programming Language (2nd ed.). Prentice Hall. ISBNvii-302-02412-10.

External links

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). (iii.61 MB)
comp.lang.c Frequently Asked Questions
A History of C, by Dennis Ritchie

This page was concluding edited on i March 2022, at 08:47

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Source: https://wiki2.org/en/C_(programming_language)