C# Reading an Mp3 File Visual Graph

Full general-purpose programming linguistic communication

C
Major implementations
The C Programming Language ^[one] (often referred to as Yard&R), the seminal book on C
Paradigm	Multi-prototype: imperative (procedural), structured
Designed past	Dennis Ritchie
Developer	Dennis Ritchie & Bong Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
Offset appeared	1972; 50 years ago (1972) ^[two]

Stable release	C17 / June 2018; three years ago (2018-06)
Preview release	C2x (N2731) / October 18, 2021; 4 months ago (2021-10-18) ^[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
Cyclone, Unified Parallel C, Dissever-C, Cilk, C*
Influenced by
B (BCPL, CPL), ALGOL 68,^[iv] assembly, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Go, Java, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Freeway, Processing, Python, Ring,^[five]Rust, Seed7, Vala, Verilog (HDL),^[six] Nim, Zig
C Programming at Wikibooks

C (, as in the letterc) is a full general-purpose, procedural reckoner programming linguistic communication supporting structured programming, lexical variable scope, and recursion, with a static type system. Past design, C provides constructs that map efficiently to typical automobile instructions. It has establish lasting employ 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 language B, C was originally developed at Bell Labs past Dennis Ritchie betwixt 1972 and 1973 to construct utilities running on Unix. Information technology was applied to re-implementing the kernel of the Unix operating organization.^[7] During the 1980s, C gradually gained popularity. It has become one of the nigh widely used programming languages,^[8] ^[ix] with C compilers from diverse vendors available for the majority of existing computer 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. It was designed to exist compiled to provide low-level access to memory and language constructs that map efficiently to car instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C program written with portability in mind can be compiled for a wide diverseness of figurer platforms and operating systems with few changes to its source code.^[10]

Since 2000, C has consistently ranked among the peak ii languages in the TIOBE index, a measure of the popularity of programming languages.^[xi]

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 lawmaking is contained within subroutines (besides called "functions", though not strictly in the sense of functional programming). Function parameters are always passed past value (except arrays). Pass-by-reference is false in C by explicitly passing pointer values. C plan source text is gratis-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements.

The C linguistic communication too exhibits the following characteristics:

The language has a small, fixed number of keywords, including a full set of control flow primitives: if/else, for, do/while, while, and switch. User-defined names are not distinguished from keywords by any kind of sigil.
Information technology has a large number of arithmetic, bitwise, and logic operators: +,+=,++,&,||, etc.
More than than 1 assignment may be performed in a single statement.
Functions:
- Function return values tin be ignored, when not needed.
- Function and information pointers allow advertisement hoc run-fourth dimension polymorphism.
- Functions may non exist defined within the lexical scope of other functions.
Information typing is static, simply weakly enforced; all data has a blazon, just implicit conversions are possible.
Announcement syntax mimics usage context. C has no "define" keyword; instead, a statement beginning with the proper name of a type is taken as a declaration. There is no "function" keyword; instead, a function is indicated by the presence of a parenthesized argument list.
User-divers (typedef) and chemical compound types are possible.
- Heterogeneous aggregate information types (struct) allow related data elements to exist accessed and assigned as a unit.
- Union is a structure with overlapping members; merely the last member stored is valid.
- Assortment indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are non first-class objects: they cannot be assigned or compared using single built-in operators. At that place is no "assortment" keyword in use or definition; instead, square brackets indicate arrays syntactically, for example calendar month[xi].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are non a distinct data type, but are conventionally implemented as goose egg-terminated character arrays.
Depression-level access to reckoner memory is possible by converting machine addresses to typed pointers.
Procedures (subroutines not returning values) are a special case of role, with an untyped return blazon void.
A preprocessor performs macro definition, source lawmaking file inclusion, and conditional compilation.
There is a bones grade 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, often through the use of external libraries (east.chiliad., the GLib Object System or the Boehm garbage collector).

Relations to other languages

Many later languages have borrowed direct or indirectly from C, including C++, C#, Unix'due south C shell, D, Get, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[6] These languages have drawn many of their control structures and other basic features from C. Most of them (Python being a dramatic exception) besides express highly like syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that tin can exist radically different.

History

Early developments

Timeline of language development
Year	C Standard^[ten]
1972	Birth
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 arrangement, originally implemented in assembly linguistic communication on a PDP-7 by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Eventually, they decided to port the operating arrangement to a PDP-11. The original PDP-11 version of Unix was also developed in assembly language.^[vii]

Thompson desired a programming language to make utilities for the new platform. At start, he tried to make a Fortran compiler, simply soon gave up the idea. Instead, he created a cut-downwardly version of the recently adult BCPL systems programming language. The official description of BCPL was non available at the time,^[12] and Thompson modified the syntax to be less wordy, producing the similar merely somewhat simpler B.^[seven] Notwithstanding, few utilities were ultimately written in B because information technology was likewise slow, and B could not take reward of PDP-xi features such every bit byte addressability.

In 1972, Ritchie started to meliorate B, near notably adding data typing for variables, which resulted in creating a new linguistic communication C.^[13] The C compiler and some utilities made with information technology were included in Version 2 Unix.^[fourteen]

At Version 4 Unix, released in Nov 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 also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I. Its original version provided but included files and simple string replacements: #include and #define of parameterless macros. Soon later that, information technology was extended, by and large past Mike Lesk and then by John Reiser, to incorporate macros with arguments and conditional compilation.^[seven]

Unix was one of the kickoff operating system kernels implemented in a language other than associates. Before instances include the Multics organisation (which was written in PL/I) and Master Control Plan (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating organization. Johnson'southward Portable C Compiler served equally the basis for several implementations of C on new platforms.^[13]

K&R C

In 1978, Brian Kernighan and Dennis Ritchie published the outset edition of The C Programming Language.^[1] This book, known to C programmers equally Thou&R, served for many years as 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 volume^[sixteen] covers the subsequently ANSI C standard, described below.

Thousand&R introduced several language features:

Standard I/O library
long int data blazon
unsigned int data type
Chemical compound assignment operators of the form =op (such as =-) were inverse to the form op= (that is, -=) to remove the semantic ambiguity created by constructs such as i=-10, which had been interpreted as i =- 10 (decrement i past 10) instead of the possibly intended i = -10 (let i be −10).

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

In early versions of C, only functions that return types other than int must be declared if used before the function definition; functions used without prior declaration were presumed to return blazon int.

For example:

                        long                                    some_function            ();                        /* int */                                    other_function            ();                        /* int */                                    calling_function            ()                        {                                                long                                    test1            ;                                                register                                    /* 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 exist omitted in G&R C, simply are required in later standards.

Since K&R function declarations did not include any information about function arguments, part parameter type checks were not performed, although some compilers would effect a alert message if a local function was called with the wrong number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Separate tools such as Unix'south lint utility were adult that (among other things) could cheque for consistency of function use across multiple source files.

In the years post-obit the publication of Chiliad&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.east., functions with no return value)
functions returning struct or marriage types (rather than pointers)
consignment for struct data types
enumerated types

The large number of extensions and lack of agreement on a standard library, together with the linguistic communication popularity and the fact that not fifty-fifty the Unix compilers precisely implemented the K&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 commission, X3J11, to plant 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 get the footing for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Linguistic communication C". This version of the language is ofttimes referred to as ANSI C, Standard C, or sometimes C89.

In 1990, the ANSI C standard (with formatting changes) was adopted past the International Organisation for Standardization (ISO) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming linguistic communication.

ANSI, like 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 yr of ISO publication.

One of the aims of the C standardization process was to produce a superset of K&R C, incorporating many of the subsequently introduced unofficial features. The standards committee likewise included several additional features such as function 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 mode 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 lawmaking is based on it. Any program written only in Standard C and without whatsoever hardware-dependent assumptions volition run correctly on whatsoever platform with a conforming C implementation, within its resources limits. Without such precautions, programs may compile but on a sure platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness.

In cases where code must be compilable past either standard-conforming or G&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and 1000&R sections to prevent the apply on a 1000&R C-based compiler of features available 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 grapheme 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 as "C99". Information technology has since been amended iii times by Technical Corrigenda.^[xix]

C99 introduced several new features, including inline functions, several new data types (including long long int and a complex type to represent complex numbers), variable-length arrays and flexible assortment 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 //, as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.

C99 is for the most part backward compatible with C90, just is stricter in some ways; in detail, a annunciation that lacks a type specifier no longer has int implicitly causeless. A standard macro __STDC_VERSION__ is divers with value 199901L to indicate that C99 support is available. GCC, Solaris Studio, and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++, nevertheless, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.^[20] ^{[ needs update ]}

In addition, back up for Unicode identifiers (variable / function names) in the grade of escaped characters (e.m. \U0001f431) is now required. Support for raw Unicode names is optional.

C11

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 support, 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 signal that C11 support is available.

C17

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

C2x

C2x is an informal proper noun for the adjacent (after C17) major C language standard revision. It 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 linguistic communication in lodge to back up exotic features such every bit fixed-point arithmetic, multiple singled-out retentivity banks, and basic I/O operations.

In 2008, the C Standards Committee published a technical report extending the C linguistic communication^[22] to accost these issues by providing a mutual standard for all implementations to adhere to. It includes a number of features non available in normal C, such every bit fixed-bespeak arithmetic, named address spaces, and basic I/O hardware addressing.

Syntax

C has a formal grammar specified by the C standard.^[23] Line endings are generally not significant in C; nevertheless, line boundaries do have significance during the preprocessing phase. Comments may appear either between the delimiters /* and */, or (since C99) post-obit // until the end of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as comment delimiters if they appear inside cord or character literals.^[24]

C source files comprise declarations and function definitions. Part definitions, in turn, contain declarations and statements. Declarations either define new types using keywords such as struct, wedlock, and enum, or assign types to and possibly reserve storage for new variables, usually by writing the blazon followed past the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }, sometimes chosen "curly brackets") to limit the scope of declarations and to act as a single statement for control structures.

As an imperative language, C uses statements to specify deportment. The nearly 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 control-flow statements identified by reserved keywords. Structured programming is supported past if … [else] conditional execution and by exercise … while, while, and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can exist omitted. break and go along can be used to leave the innermost enclosing loop statement or skip to its reinitialization. There is also a non-structured goto argument which branches straight to the designated label within the part. switch selects a case to be executed based on the value of an integer expression.

Expressions tin can use a variety of built-in operators and may comprise function calls. The order in which arguments to functions and operands to nigh operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side furnishings (including storage to variables) will occur earlier the next "sequence point"; sequence points include the end of each expression statement, and the entry to and return from each function phone call. Sequence points likewise occur during evaluation of expressions containing sure operators (&&, ||, ?: and the comma operator). This permits a loftier degree of object code optimization by the compiler, but requires C programmers to accept 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 language, has its blemishes. Some of the operators have the incorrect precedence; some parts of the syntax could exist amend."^[25] The C standard did non endeavor to correct many of these blemishes, because of the bear upon of such changes on already existing software.

Grapheme prepare

The bones C source character fix includes the post-obit characters:

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

Newline indicates the end of a text line; it need not stand for to an actual unmarried grapheme, although for convenience C treats it as ane.

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

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

Reserved words

C89 has 32 reserved words, also known as 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
do
double
else
enum
extern
bladder
for
goto
if
int
long
register
return
short
signed
sizeof
static
struct
switch
typedef
union
unsigned
void
volatile
while

C99 reserved v more words:

_Bool
_Complex
_Imaginary
inline
restrict

C11 reserved vii more than words:^[26]

_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert
_Thread_local

Nigh of the recently reserved words brainstorm with an underscore followed past a capital letter alphabetic character, because identifiers of that class were previously reserved by the C standard for use just by implementations. Since existing program source code should not take been using these identifiers, it would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers exercise define more convenient synonyms for underscored identifiers. The linguistic communication previously included a reserved word called entry, only this was seldom implemented, and has now been removed equally a reserved word.^[27]

Operators

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

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

C uses the operator = (used in mathematics to express equality) to signal consignment, post-obit the precedent of Fortran and PL/I, but unlike ALGOL and its derivatives. C uses the operator == to examination for equality. The similarity between these two operators (assignment and equality) may result in the accidental use of one in place of the other, and in many cases, the mistake does not produce an error message (although some compilers produce warnings). For example, the conditional expression if (a == b + 1) might mistakenly exist written every bit if (a = b + 1), which will exist evaluated as truthful if a is non goose egg after the assignment.^[28]

The C operator precedence is not always intuitive. For example, the operator == binds more tightly than (is executed prior to) the operators & (bitwise AND) and | (bitwise OR) in expressions such as 10 & 1 == 0, which must exist written equally (x & i) == 0 if that is the coder's intent.^[29]

"Hi, earth" example

The "how-do-you-do, earth" example, which appeared in the offset 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 ordinarily a final or screen display.

The original version was:^[30]

                        principal            ()                        {                                                printf            (            "how-do-you-do, world            \n            "            );                        }

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

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

The commencement line of the program contains a preprocessing directive, indicated past #include. This causes the compiler to replace 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 angle 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 projection-specific header files.

The adjacent line indicates that a function named chief is being defined. The main function serves a special purpose in C programs; the run-time environment calls the master role to begin program execution. The type specifier int indicates that the value that is returned to the invoker (in this instance the run-time surround) as a result of evaluating the primary part, is an integer. The keyword void as a parameter list indicates that this function takes no arguments.^[b]

The opening curly caryatid indicates the get-go of the definition of the main function.

The next line calls (diverts execution to) a function named printf, which in this case is supplied from a system library. In this call, the printf part is passed (provided with) a single argument, the address of the first character in the string literal "hello, world\n". The string literal is an unnamed array with elements of type char, set up up automatically past the compiler with a final 0-valued character to mark the end of the array (printf needs to know this). The \n is an escape sequence that C translates to a newline character, which on output signifies the end of the current line. The return value of the printf part is of type int, but it is silently discarded since it is not used. (A more conscientious program might exam the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement.

The closing curly brace indicates the terminate of the code for the main office. According to the C99 specification and newer, the main function, unlike any other function, 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 past the run-fourth dimension organization as an leave code indicating successful execution.^[31]

Data types

The type system in C is static and weakly typed, which makes information technology similar to the type organisation of ALGOL descendants such every bit Pascal.^[32] At that place are built-in types for integers of diverse sizes, both signed and unsigned, floating-point 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 often used in low-level systems programming where escapes from the blazon system may exist necessary. The compiler attempts to ensure type correctness of most expressions, just the programmer can override the checks in various means, either by using a type bandage to explicitly convert a value from one type to some other, or by using pointers or unions to reinterpret the underlying bits of a information object in some other mode.

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

C's usual arithmetic conversions let for efficient lawmaking to exist generated, but tin 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

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

A null arrow value explicitly points to no valid location. Dereferencing a naught arrow value is undefined, often resulting in a partitioning mistake. Null arrow values are useful for indicating special cases such as no "next" pointer in the last 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 arrow variable, a null arrow constant can exist written equally 0, with or without explicit casting to a pointer type, or as the NULL macro divers by several standard headers. In provisional contexts, null pointer values evaluate to false, while all other arrow values evaluate to truthful.

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

Careless utilise of pointers is potentially unsafe. Because they are typically unchecked, a pointer variable can be fabricated to point to whatever arbitrary location, which can cause undesirable effects. Although properly used pointers signal to safety places, they tin exist made to point to unsafe places by using invalid pointer arithmetic; the objects they point to may continue to be 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 bandage, union, or through another corrupt pointer. In general, C is permissive in assuasive manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these bug by using more than restrictive reference types.

Arrays

Array types in C are traditionally of a fixed, static size specified at compile time. The more than contempo C99 standard as well allows a form of variable-length arrays. Withal, information technology is as well possible to allocate a block of memory (of arbitrary size) at run-time, using the standard library's malloc office, and treat information technology as an array.

Since arrays are always accessed (in issue) 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 premises violations are therefore possible and tin can lead to various repercussions, including illegal memory accesses, corruption of data, buffer overruns, and run-time exceptions.

C does not have a special provision for declaring multi-dimensional arrays, just rather relies on recursion within the type organization to declare arrays of arrays, which effectively accomplishes the aforementioned thing. The index values of the resulting "multi-dimensional assortment" can be thought of equally increasing in row-major society. Multi-dimensional arrays are commonly used in numerical algorithms (mainly from applied linear algebra) to store matrices. The construction of the C assortment is well suited to this detail task. However, in early versions of C the premises of the assortment must exist known stock-still 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 classify the array with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this result.

The following instance using mod C (C99 or afterwards) shows resource allotment of a two-dimensional array on the heap and the use of multi-dimensional array indexing for accesses (which tin employ bounds-checking on many C compilers):

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

Array–pointer interchangeability

The subscript notation x[i] (where 10 designates a pointer) is syntactic saccharide for *(x+i).^[36] Taking advantage of the compiler's knowledge of the pointer blazon, the address that ten + i points to is not the base address (pointed to by x) incremented by i bytes, but rather is defined to be the base of operations address incremented by i multiplied by the size of an element that ten 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 kickoff chemical element. This implies that an array is never copied as a whole when named equally an argument to a office, simply rather only the address of its first element is passed. Therefore, although function calls in C utilise pass-by-value semantics, arrays are in effect passed by reference.

The total size of an assortment ten can exist determined by applying sizeof to an expression of array blazon. The size of an element tin can be adamant by applying the operator sizeof to any dereferenced element of an array A, every bit in n = sizeof A[0]. This, the number of elements in a alleged array A tin can be determined as sizeof A / sizeof A[0]. Notation, that if only a pointer to the first element is available as it is ofttimes the case in C code considering of the automatic conversion described above, the information about the full type of the array and its length are lost.

Retentiveness management

Ane of the nigh important functions of a programming language is to provide facilities for managing retention and the objects that are stored in retentivity. C provides three singled-out means to classify memory 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 every bit the binary which contains them is loaded into memory.
Automated memory allocation: temporary objects can be stored on the stack, and this infinite is automatically freed and reusable later the cake in which they are declared is exited.
Dynamic memory resource allotment: blocks of retentivity of arbitrary size can be requested at run-time using library functions such as malloc from a region of retentivity chosen the heap; these blocks persist until subsequently freed for reuse by calling the library function realloc or free

These three approaches are advisable in dissimilar situations and have various trade-offs. For instance, static retentivity allocation has little resource allotment overhead, automatic allocation may involve slightly more overhead, and dynamic retentiveness allotment can potentially have a swell bargain of overhead for both allocation and deallocation. The persistent nature of static objects is useful for maintaining state information across function calls, automatic allocation is easy to use but stack space is typically much more limited and transient than either static memory or heap space, and dynamic memory allotment allows convenient allocation of objects whose size is known only at run-time. Nigh C programs make extensive utilise of all iii.

Where possible, automatic or static allocation is ordinarily simplest considering the storage is managed by the compiler, freeing the developer of the potentially error-prone chore of manually allocating and releasing storage. All the same, many data structures can change in size at runtime, and since static allocations (and automatic allocations before C99) must accept 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. (Meet the article on malloc for an example of dynamically allocated arrays.) Unlike automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a zip pointer value) when the required storage cannot be allocated. (Static allocation that is as well large is usually detected by the linker or loader, before the programme can fifty-fifty begin execution.)

Unless otherwise specified, static objects incorporate cypher or cypher arrow values upon programme startup. Automatically and dynamically allocated objects are initialized merely if an initial value is explicitly specified; otherwise they initially accept indeterminate values (typically, whatsoever fleck pattern happens to be present in the storage, which might not fifty-fifty stand for a valid value for that type). If the plan attempts to access an uninitialized value, the results are undefined. Many modern compilers try to find and warn nigh this problem, but both false 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 as possible. For example, if the only pointer to a heap retentiveness allocation goes out of telescopic or has its value overwritten before it is deallocated explicitly, so that retention cannot be recovered for after reuse and is essentially lost to the program, a phenomenon known equally a memory leak. Conversely, information technology 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 code that causes the mistake, making information technology hard to diagnose the failure. Such issues 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 set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained inside the library that may exist used past a program, and declarations of special data types and macro symbols used with these functions. In social club for a program to use a library, it must include the library's header file, and the library must exist linked with the plan, which in many cases requires compiler flags (e.g., -lm, shorthand for "link the math library").^[31]

The near 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 only a subset of the standard library). This library supports stream input and output, memory allocation, mathematics, graphic symbol strings, and fourth dimension values. Several separate standard headers (for example, stdio.h) specify the interfaces for these and other standard library facilities.

Another mutual set up 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 diverse 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 then create interfaces to the library so that the routines tin can exist used from higher-level languages like Java, Perl, and Python.^[31]

File treatment and streams

File input and output (I/O) is non part of the C language itself but instead is handled past libraries (such as the C standard library) and their associated header files (due east.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 period that is independent of devices, while a file is a concrete device. The high-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 shop data before it'south sent to the final destination. This reduces the time spent waiting for slower devices, for example a hard drive or solid land drive. Low-level I/O functions are not part of the standard C library^{[ clarification needed ]} simply are by and large function of "bare metallic" programming (programming that'southward contained of whatever operating organization such as most embedded programming). With few exceptions, implementations include low-level I/O.

Language tools

A number of tools have been adult to assist C programmers discover and set statements with undefined behavior or perhaps erroneous expressions, with greater rigor than that provided past the compiler. The tool lint was the commencement such, leading to many others.

Automatic source code checking and auditing are beneficial in any language, and for C many such tools exist, such equally Lint. A common exercise is to utilise Lint to detect questionable code when a program is starting time written. Once a programme passes Lint, information technology is then compiled using the C compiler. Also, many compilers can optionally warn about syntactically valid constructs that are likely to really be errors. MISRA C is a proprietary ready of guidelines to avoid such questionable lawmaking, adult for embedded systems.^[37]

In that location are also compilers, libraries, and operating arrangement level mechanisms for performing deportment that are not a standard part of C, such as bounds checking for arrays, detection of buffer overflow, serialization, dynamic memory tracking, and automatic garbage collection.

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

Uses

The C Programming Linguistic communication

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

C can be used for website programming using the Mutual Gateway Interface (CGI) every bit a "gateway" for information betwixt the Web application, the server, and the browser.^[39] C is often chosen over interpreted languages because of its speed, stability, and nigh-universal availability.^[40]

A effect of C'southward broad availability and efficiency is that compilers, libraries and interpreters of other programming languages are often implemented in C. For case, the reference implementations of Python, Perl, Ruby, and PHP are written in C.

C enables programmers to create efficient implementations of algorithms and information structures, considering the layer of brainchild from hardware is thin, and its overhead is low, an of import 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 be used for portability or convenience; past using C every bit an intermediate language, additional automobile-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 code. All the same, some of C's shortcomings have prompted the evolution of other C-based languages specifically designed for utilise as intermediate languages, such as C--.

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

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

C has both directly and indirectly influenced many after languages such as C#, D, Go, Java, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix'due south C vanquish.^[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, data 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 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 lawmaking was translated into C, and so compiled with a C compiler.^[43]

The C++ programming language (originally named "C with Classes") was devised past 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. Most a superset of C, C++ now supports most of C, with a few exceptions.

Objective-C was originally a very "thin" layer on meridian of C, and remains a strict superset of C that permits object-oriented programming using a hybrid dynamic/static typing paradigm. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations, and 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

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

^ The original example code will compile on most modernistic compilers that are not in strict standard compliance manner, but 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 office actually has two arguments, int argc and char *argv[], respectively, which can exist used to handle command line arguments. The ISO C standard (department v.one.two.two.1) requires both forms of main to be supported, which is special handling non afforded to any other role.

References

^ ^a ^b Kernighan, Brian Due west.; Ritchie, Dennis M. (February 1978). The C Programming Language (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110163-0.
^ Ritchie (1993): "Thompson had fabricated a brief attempt to produce a system coded in an early on version of C—before structures—in 1972, merely gave upward the try."
^ 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 composition adopted by C owes considerable debt to Algol 68, although it did non, perchance, sally in a grade that Algol's adherents would approve of."
^ Ring Team (October 23, 2021). "The Band programming language and other languages". ring-lang.net.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Enquiry School of Computer Scientific discipline at the Australian National Academy. June 3, 2010. Archived from the original (PDF) on November 6, 2013. Retrieved August 19, 2013. 1980s: ; Verilog outset 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 16, 2009. Retrieved January 16, 2009.
^ "TIOBE Programming Community Alphabetize". 2009. Archived from the original on May iv, 2009. Retrieved May vi, 2009.
^ ^a ^b "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
^ "TIOBE Alphabetize for Oct 2021". Retrieved October 7, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on December 12, 2019. Retrieved September 10, 2019.
^ ^a ^b Johnson, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX Arrangement". Bell System Tech. J. 57 (vi): 2021–2048. CiteSeerX10.1.1.138.35. doi:x.1002/j.1538-7305.1978.tb02141.x. S2CID 17510065. (Notation: The PDF is an OCR scan of the original, and contains a rendering of "IBM 370" as "IBM 310".)
^ McIlroy, G. D. (1987). A Research Unix reader: annotated excerpts from the Developer'southward Manual, 1971–1986 (PDF) (Technical report). CSTR. Bong Labs. p. 10. 139. Archived (PDF) from the original on November xi, 2017. Retrieved February 1, 2015.
^ "C manual pages". FreeBSD Miscellaneous Data Manual (FreeBSD xiii.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 Due west.; Ritchie, Dennis M. (March 1988). The C Programming Linguistic communication (2d ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110362-seven.
^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Report). AT&T Labs. Archived (PDF) from the original on Baronial 24, 2014. Retrieved April 14, 2014.
^ C Integrity. International Arrangement for Standardization. March 30, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
^ "JTC1/SC22/WG14 – C". Home page. ISO/IEC. Archived from the original on Feb 12, 2018. Retrieved June 2, 2011.
^ Andrew Binstock (October 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on Baronial 2, 2013. Retrieved September vii, 2013.
^ "Revised C23 Schedule WG xiv N 2759" (PDF). world wide web.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October 10, 2021.
^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on Feb 25, 2021. Retrieved July 26, 2011.
^ Harbison, Samuel P.; Steele, Guy Fifty. (2002). C: A Reference Manual (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-9. Contains a BNF grammar for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. three.
^ "ISO/IEC 9899:201x (ISO C11) Commission Draft" (PDF). Archived (PDF) from the original on December 22, 2017. Retrieved September 16, 2011.
^ Kernighan & Ritchie (1996), pp. 192, 259.
^ "x Common Programming Mistakes in C++". Cs.ucr.edu. Archived from the original on October 21, 2008. Retrieved June 26, 2009.
^ Schultz, Thomas (2004). C and the 8051 (3rd ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-one-58961-237-2. Archived from the original on July 29, 2020. Retrieved February 10, 2012.
^ Kernighan & Ritchie (1978), p. 6.
^ ^a ^b ^c ^d ^e ^f ^thousand Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-1-4493-2714-9.
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^ Raymond, Eric S. (Oct 11, 1996). The New Hacker's Dictionary (3rd ed.). MIT Press. p. 432. ISBN978-0-262-68092-9. Archived from the original on November 12, 2012. Retrieved August v, 2012.
^ "Human being Folio for lint (freebsd Section ane)". unix.com. May 24, 2001. Retrieved July 15, 2014.
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Sources

Ritchie, Dennis M. (March 1993). "The Development of the C Language". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:x.1145/155360.155580.
Ritchie, Dennis M. (1993). "The Development of the C Linguistic communication". The Second ACM SIGPLAN Briefing on History of Programming Languages (HOPL-II). ACM. pp. 201–208. doi:ten.1145/154766.155580. ISBN0-89791-570-iv . Retrieved November iv, 2014.
Kernighan, Brian Westward.; Ritchie, Dennis M. (1996). The C Programming Language (2d ed.). Prentice Hall. ISBN7-302-02412-10.

Farther reading

Kernighan, Brian; Ritchie, Dennis (1988). The C Programming Language (2 ed.). Prentice Hall. ISBN978-0131103627. (archive)
Plauger, P.J. (1992). The Standard C Library (1 ed.). Prentice Hall. ISBN978-0131315099. (source)
Banahan, M.; Brady, D.; Doran, M. (1991). The C Book: Featuring the ANSI C Standard (2 ed.). Addison-Wesley. ISBN978-0201544336. (complimentary)
Harbison, Samuel; Steele Jr, Guy (2002). C: A Reference Manual (five ed.). Pearson. ISBN978-0130895929. (annal)
Rex, Grand.Due north. (2008). C Programming: A Modernistic Approach (2 ed.). W. Westward. Norton. ISBN978-0393979503. (archive)
Griffiths, David; Griffiths, Dawn (2012). Head Offset C (one 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 Programme (eight ed.). Pearson. ISBN978-0133976892.
Gustedt, Jens (2019). Modernistic C (2 ed.). Manning. ISBN978-1617295812. (complimentary)

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 final edited on ane March 2022, at 08:47

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