C# Read and Write Csv at Same Time

General-purpose programming language

C
Major implementations
The C Programming Language ^[1] (oftentimes referred to equally Grand&R), the seminal volume on C
Paradigm	Multi-paradigm: imperative (procedural), structured
Designed by	Dennis Ritchie
Developer	Dennis Ritchie & Bell Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
Starting time appeared	1972; l years ago (1972) ^[2]

Stable release	C17 / June 2018; iii years ago (2018-06)
Preview release	C2x (N2731) / October 18, 2021; 4 months ago (2021-10-18) ^[3]

Typing discipline	Static, weak, manifest, nominal
Bone	Cantankerous-platform
Filename extensions	.c, .h
Website	www.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, Separate-C, Cilk, C*
Influenced by
B (BCPL, CPL), ALGOL 68,^[4] assembly, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Go, Java, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Motorway, Processing, Python, Ring,^[5]Rust, Seed7, Vala, Verilog (HDL),^{[half dozen]} Nim, Zig
C Programming at Wikibooks

C (, as in the letterc) is a general-purpose, procedural computer programming language supporting structured programming, lexical variable telescopic, and recursion, with a static blazon system. By design, C provides constructs that map efficiently to typical machine instructions. It has constitute lasting utilise in applications previously coded in associates language. Such applications include operating systems and various application software for reckoner 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. Information technology was applied to re-implementing the kernel of the Unix operating arrangement.^[7] During the 1980s, C gradually gained popularity. It has become one of the most widely used programming languages,^[8] ^[9] with C compilers from diverse vendors available for the majority of existing figurer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and by the International Arrangement for Standardization (ISO).

C is an imperative procedural language. It was designed to be compiled to provide depression-level access to memory and language constructs that map efficiently to machine instructions, all with minimal runtime back up. 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 be compiled for a wide diversity of reckoner platforms and operating systems with few changes to its source lawmaking.^[10]

Since 2000, C has consistently ranked among the top 2 languages in the TIOBE index, a measure 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 independent within subroutines (also called "functions", though not strictly in the sense of functional programming). Function parameters are always passed by value (except arrays). Pass-past-reference is simulated in C by explicitly passing arrow values. C program source text is free-format, using the semicolon as a statement terminator and curly braces for group blocks of statements.

The C language too exhibits the following characteristics:

The language has a small, fixed number of keywords, including a full set of control catamenia primitives: if/else, for, practice/while, while, and switch. User-defined names are not distinguished from keywords by whatsoever kind of sigil.
It has a large number of arithmetic, bitwise, and logic operators: +,+=,++,&,||, etc.
More than i assignment may be performed in a single statement.
Functions:
- Part return values can exist ignored, when non needed.
- Function and data pointers permit advertizing hoc run-time polymorphism.
- Functions may not exist divers inside the lexical scope of other functions.
Data typing is static, simply weakly enforced; all information has a type, simply implicit conversions are possible.
Declaration syntax mimics usage context. C has no "define" keyword; instead, a statement offset with the proper noun of a blazon is taken every bit a declaration. There is no "role" keyword; instead, a function is indicated by the presence of a parenthesized statement list.
User-defined (typedef) and compound types are possible.
- Heterogeneous amass data types (struct) let related data elements to be accessed and assigned every bit a unit of measurement.
- Union is a structure with overlapping members; only the terminal fellow member stored is valid.
- Array indexing is a secondary notation, defined in terms of pointer arithmetic. Different structs, arrays are not splendid objects: they cannot be assigned or compared using single built-in operators. There is no "assortment" keyword in use or definition; instead, foursquare brackets indicate arrays syntactically, for example calendar 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 null-terminated graphic symbol arrays.
Low-level access to computer retentivity is possible by converting auto addresses to typed pointers.
Procedures (subroutines not returning values) are a special case of function, with an untyped return type void.
A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
There is a bones grade of modularity: files tin be compiled separately and linked together, with control over which functions and data objects are visible to other files via static and extern attributes.
Complex functionality such equally I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does not include certain features found in other languages (such equally object orientation and garbage collection), these tin can be implemented or emulated, often through the employ of external libraries (eastward.k., the GLib Object System or the Boehm garbage collector).

Relations to other languages

Many later on languages accept borrowed directly or indirectly from C, including C++, C#, Unix'due south C beat out, D, Go, 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 fatigued many of their control structures and other basic features from C. Most of them (Python beingness a dramatic exception) as well limited highly similar syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying blazon systems, data models, and semantics that can exist radically different.

History

Early developments

Timeline of language development
Year	C Standard^[10]
1972	Nascency
1978	Chiliad&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 evolution of the Unix operating system, originally implemented in associates language on a PDP-7 by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Somewhen, they decided to port the operating arrangement to a PDP-11. The original PDP-11 version of Unix was also developed in assembly language.^[7]

Thompson desired a programming language to make utilities for the new platform. At first, he tried to make a Fortran compiler, simply soon gave up the thought. Instead, he created a cut-downward version of the recently developed BCPL systems programming language. The official description of BCPL was not available at the fourth dimension,^[12] and Thompson modified the syntax to exist less wordy, producing the similar but somewhat simpler B.^[7] However, few utilities were ultimately written in B considering it was also wearisome, and B could not take advantage of PDP-11 features such equally byte addressability.

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

At Version 4 Unix, released in Nov 1973, the Unix kernel was extensively re-implemented in C.^[vii] Past this time, the C language had caused some powerful features such as struct types.

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

Unix was ane of the get-go operating arrangement kernels implemented in a language other than associates. Earlier instances include the Multics system (which was written in PL/I) and Master Command Plan (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In effectually 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson'south Portable C Compiler served as the basis for several implementations of C on new platforms.^[13]

Grand&R C

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Linguistic communication.^[1] This book, known to C programmers as K&R, served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as "K&R C". As this was released in 1978, it is also referred to every bit C78.^[15] The 2nd edition of the book^[16] covers the later ANSI C standard, described beneath.

Thousand&R introduced several language features:

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

Even afterward the publication of the 1989 ANSI standard, for many years K&R C was yet 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 1000&R C code tin be legal Standard C every bit well.

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

For case:

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

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

Since K&R part declarations did not include any information about function arguments, function parameter blazon checks were non performed, although some compilers would event a warning bulletin if a local function was called with the incorrect number of arguments, or if multiple calls to an external office used different numbers or types of arguments. Divide tools such as Unix's lint utility were developed that (amongst other things) could check for consistency of function apply across multiple source files.

In the years following the publication of One thousand&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.e., functions with no return value)
functions returning struct or union types (rather than pointers)
assignment 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 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, equally 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; even so, 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 every bit ANSI X3.159-1989 "Programming Language C". This version of the linguistic communication is ofttimes referred to as ANSI C, Standard C, or sometimes C89.

In 1990, the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) equally 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 group ISO/IEC JTC1/SC22/WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication.

One of the aims of the C standardization procedure was to produce a superset of K&R C, incorporating many of the after introduced unofficial features. The standards committee as well 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 style used in C++, the 1000&R interface continued to exist permitted, for compatibility with existing source lawmaking.

C89 is supported by current C compilers, and most modern C code is based on it. Whatsoever programme written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a befitting C implementation, within its resource limits. Without such precautions, programs may compile but on a certain platform or with a detail compiler, due, for example, to the apply of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such every bit the verbal size of data types and byte endianness.

In cases where code must be compilable by either standard-conforming or Chiliad&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and Yard&R sections to prevent the utilise on a Thou&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 character sets.^[xviii]

C99

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

C99 introduced several new features, including inline functions, several new information types (including long long int and a circuitous blazon to represent complex numbers), variable-length arrays and flexible array members, improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity), and back up 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 nearly part backward compatible with C90, but is stricter in some ways; in detail, a announcement 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 back up is bachelor. 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++, even so, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.^[20] ^{[ needs update ]}

In add-on, back up for Unicode identifiers (variable / role names) in the form of escaped characters (e.g. \U0001f431) is at present required. Back up for raw Unicode names is optional.

C11

In 2007, piece of work began on another 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 by 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 bespeak 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, 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 next (after C17) major C language standard revision. It is expected to exist voted on in 2023 and would therefore exist called C23.^[21] ^{[ meliorate source needed ]}

Embedded C

Historically, embedded C programming requires nonstandard extensions to the C language in order to support exotic features such every bit stock-still-point arithmetic, multiple distinct retentivity banks, and basic I/O operations.

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

Syntax

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

C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either define new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, commonly by writing the type followed past the variable proper noun. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }, sometimes called "curly brackets") to limit the scope of declarations and to human activity as a single statement for command structures.

Every bit an imperative language, C uses statements to specify actions. The well-nigh common statement is an expression statement, consisting of an expression to exist evaluated, followed past a semicolon; equally a side effect of the evaluation, functions may be called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several control-menstruation statements identified by reserved keywords. Structured programming is supported by if … [else] conditional execution and past do … while, while, and for iterative execution (looping). The for statement has divide initialization, testing, and reinitialization expressions, whatsoever or all of which can exist omitted. intermission and continue tin be used to leave the innermost enclosing loop statement or skip to its reinitialization. In that location is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression.

Expressions can use a variety of congenital-in operators and may contain function calls. The order in which arguments to functions and operands to nearly operators are evaluated is unspecified. The evaluations may fifty-fifty 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 argument, and the entry to and return from each function telephone call. Sequence points also occur during evaluation of expressions containing sure operators (&&, ||, ?: and the comma operator). This permits a high 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 Linguistic communication: "C, similar any other language, has its blemishes. Some of the operators have the incorrect precedence; some parts of the syntax could be meliorate."^[25] The C standard did not attempt to correct many of these blemishes, because of the impact of such changes on already existing software.

Character set

The basic C source character ready includes the post-obit characters:

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

Newline indicates the end of a text line; information technology need not correspond to an actual single character, although for convenience C treats information technology as i.

Additional multi-byte encoded characters may exist used in string literals, but they are non 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 graphic symbol), although this feature is not yet widely implemented.

The basic C execution character gear up contains the same characters, along with representations for warning, 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 every bit keywords, which are the words that cannot be used for any purposes other than those for which they are predefined:

auto
break
instance
char
const
go on
default
exercise
double
else
enum
extern
float
for
goto
if
int
long
register
render
short
signed
sizeof
static
struct
switch
typedef
union
unsigned
void
volatile
while

C99 reserved five more words:

_Bool
_Complex
_Imaginary
inline
restrict

C11 reserved seven more words:^[26]

_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert
_Thread_local

Most of the recently reserved words brainstorm with an underscore followed by a capital letter, considering identifiers of that form were previously reserved by the C standard for use only by implementations. Since existing program source code should not take been using these identifiers, information technology would non be affected when C implementations started supporting these extensions to the programming linguistic communication. Some standard headers do ascertain more convenient synonyms for underscored identifiers. The language previously included a reserved word called entry, but this was seldom implemented, and has now 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 exist performed while evaluating that expression. C has operators for:

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

C uses the operator = (used in mathematics to express equality) to indicate assignment, post-obit 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 2 operators (assignment and equality) may effect in the accidental use of one in place of the other, and in many cases, the mistake does not produce an mistake message (although some compilers produce warnings). For example, the conditional expression if (a == b + 1) might mistakenly exist written as if (a = b + i), which will be evaluated every bit truthful if a is not zero after the assignment.^[28]

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

"Hello, world" instance

The "hi, world" example, which appeared in the starting time edition of Yard&R, has go the model for an introductory program in most programming textbooks. The program prints "hello, world" to the standard output, which is ordinarily a final or screen display.

The original version was:^[30]

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

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

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

The showtime line of the programme contains a preprocessing directive, indicated by #include. This causes the compiler to supervene upon 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 project-specific header files.

The next line indicates that a function named main is being divers. The main role serves a special purpose in C programs; the run-time environment calls the main function to brainstorm program execution. The type specifier int indicates that the value that is returned to the invoker (in this example the run-fourth dimension environment) every bit a issue of evaluating the main function, is an integer. The keyword void as a parameter list indicates that this function takes no arguments.^[b]

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

The side by side line calls (diverts execution to) a role named printf, which in this example is supplied from a system library. In this call, the printf function is passed (provided with) a single argument, the address of the commencement character in the string literal "hello, earth\north". The string literal is an unnamed array with elements of blazon char, set automatically by the compiler with a concluding 0-valued character to mark the end of the assortment (printf needs to know this). The \n is an escape sequence that C translates to a newline character, which on output signifies the end of the electric current line. The return value of the printf office is of type int, only it is silently discarded since it is not used. (A more than conscientious plan might exam the return value to determine whether or not the printf part succeeded.) The semicolon ; terminates the argument.

The closing curly caryatid indicates the cease of the code for the main function. Co-ordinate to the C99 specification and newer, the chief office, unlike any other function, will implicitly return a value of 0 upon reaching the } that terminates the part. (Formerly an explicit return 0; statement was required.) This is interpreted by the run-fourth dimension system as an exit code indicating successful execution.^[31]

Data types

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

C is often used in low-level systems programming where escapes from the blazon organisation may exist necessary. The compiler attempts to ensure type correctness of nearly expressions, just the developer can override the checks in various ways, either past using a type bandage to explicitly convert a value from one type to another, or by using pointers or unions to reinterpret the underlying $.25 of a data object in some other mode.

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

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

Pointers

C supports the use 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 information stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or pointer arithmetic. The run-fourth dimension representation of a pointer value is typically a raw retention address (perhaps augmented by an offset-within-word field), but since a arrow's type includes the type of the thing pointed to, expressions including pointers tin can be type-checked at compile fourth dimension. Arrow arithmetic is automatically scaled by 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 data types, such as copse, are usually implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to higher-order functions (such every bit qsort or bsearch) or equally callbacks to be invoked by consequence handlers.^[31]

A zip pointer value explicitly points to no valid location. Dereferencing a nothing pointer value is undefined, often resulting in a sectionalization error. Null pointer values are useful for indicating special cases such as no "adjacent" pointer in the terminal 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 pointer constant tin can be written every bit 0, with or without explicit casting to a pointer blazon, or as the Aught macro divers by several standard headers. In conditional contexts, null pointer values evaluate to simulated, while all other pointer values evaluate to true.

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

Careless employ of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable can be made to point to whatsoever arbitrary location, which tin cause undesirable effects. Although properly used pointers indicate to condom places, they can be made to point to unsafe places past using invalid arrow arithmetic; the objects they point to may continue to exist used subsequently 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 full 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 restrictive reference types.

Arrays

Array types in C are traditionally of a fixed, static size specified at compile time. The more recent C99 standard also allows a grade of variable-length arrays. However, it is also possible to allocate a block of retentivity (of arbitrary size) at run-time, using the standard library's malloc function, and care for information technology as an array.

Since arrays are always accessed (in consequence) via pointers, array accesses are typically not checked against the underlying array size, although some compilers may provide bounds checking as an choice.^[34] ^[35] Array premises violations are therefore possible and tin can lead to various repercussions, including illegal retentiveness accesses, corruption of data, buffer overruns, and run-time exceptions.

C does non have a special provision for declaring multi-dimensional arrays, but rather relies on recursion within the type organisation to declare arrays of arrays, which finer accomplishes the same affair. The index values of the resulting "multi-dimensional array" can be thought of every bit increasing in row-major lodge. Multi-dimensional arrays are commonly used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C array is well suited to this item job. Yet, in early on versions of C the bounds of the array must be known fixed values or else explicitly passed to whatsoever subroutine that requires them, and dynamically sized arrays of arrays cannot exist accessed using double indexing. (A workaround for this was to allocate the assortment with an boosted "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this issue.

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

                        int                                    func            (            int                                    N            ,                                    int                                    M            )                        {                                                float                                    (            *            p            )[            North            ][            M            ]                                    =                                    malloc            (            sizeof                                    *            p            );                                                if                                    (            !            p            )                                                return                                    -ane            ;                                                for                                    (            int                                    i                                    =                                    0            ;                                    i                                    <                                    N            ;                                    i            ++            )                                                for                                    (            int                                    j                                    =                                    0            ;                                    j                                    <                                    Grand            ;                                    j            ++            )                                                (            *            p            )[            i            ][            j            ]                                    =                                    i                                    +                                    j            ;                                                print_array            (            North            ,                                    M            ,                                    p            );                                                free            (            p            );                                                return                                    i            ;                        }

Array–arrow interchangeability

The subscript notation ten[i] (where x designates a pointer) is syntactic sugar for *(x+i).^[36] Taking advantage of the compiler'due south knowledge of the pointer type, the address that 10 + i points to is non the base accost (pointed to by x) incremented past i bytes, only rather is divers to be the base accost incremented by i multiplied by the size of an element that x points to. Thus, x[i] designates the i+1th element of the assortment.

Furthermore, in well-nigh expression contexts (a notable exception is as operand of sizeof), an expression of array type is automatically converted to a pointer to the assortment'due south first element. This implies that an array is never copied every bit a whole when named every bit an argument to a role, just rather only the address of its start chemical element is passed. Therefore, although function calls in C utilise pass-by-value semantics, arrays are in issue passed by reference.

The total size of an array x can be determined by applying sizeof to an expression of assortment type. The size of an element can be determined by applying the operator sizeof to any dereferenced chemical element of an array A, as in n = sizeof A[0]. This, the number of elements in a declared array A tin can exist determined as sizeof A / sizeof A[0]. Note, that if simply a pointer to the first element is available as it is often the instance in C lawmaking considering of the automatic conversion described above, the information about the full blazon of the array and its length are lost.

Retention management

One of the most important functions of a programming language is to provide facilities for managing memory and the objects that are stored in memory. C provides three singled-out ways to classify retentivity for objects:^[31]

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

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

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

Unless otherwise specified, static objects contain cypher or null pointer values upon programme startup. Automatically and dynamically allocated objects are initialized only if an initial value is explicitly specified; otherwise they initially have indeterminate values (typically, whatever bit blueprint happens to exist present in the storage, which might not even stand for a valid value for that blazon). If the program attempts to access an uninitialized value, the results are undefined. Many modernistic compilers try to find and warn virtually this problem, but both imitation positives and fake negatives can occur.

Heap memory allocation has to be synchronized with its actual usage in whatever program to be reused every bit much as possible. For example, if the merely arrow to a heap retention allocation goes out of scope or has its value overwritten before it is deallocated explicitly, then that memory cannot be recovered for after 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 announced in a portion of the programme unrelated to the code that causes the mistake, making it difficult 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 set up of functions contained within a single "annal" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a program, and declarations of special data types and macro symbols used with these functions. In order for a program to use a library, it must include the library'south header file, and the library must be linked with the program, which in many cases requires compiler flags (due east.g., -lm, autograph for "link the math library").^[31]

The about 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 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, character strings, and fourth dimension values. Several separate standard headers (for instance, stdio.h) specify the interfaces for these and other standard library facilities.

Another common fix of C library functions are those used by applications specifically targeted for Unix and Unix-like systems, especially functions which provide an interface to the kernel. These functions are detailed in various standards such every bit POSIX and the Single UNIX Specification.

Since many programs take been written in C, there are a wide variety of other libraries bachelor. Libraries are often written in C because C compilers generate efficient object lawmaking; programmers then create interfaces to the library so that the routines can exist used from higher-level languages similar Java, Perl, and Python.^[31]

File handling and streams

File input and output (I/O) is not part of the C language itself but instead is handled by libraries (such as the C standard library) and their associated header files (e.thou. stdio.h). File handling is generally implemented through high-level I/O which works through streams. A stream is from this perspective a data catamenia that is independent of devices, while a file is a concrete device. The high-level I/O is done through the clan of a stream to a file. In the C standard library, a buffer (a memory area or queue) is temporarily used to store data earlier it's sent to the final destination. This reduces the fourth dimension spent waiting for slower devices, for example a hard drive or solid state drive. Low-level I/O functions are not function of the standard C library^{[ clarification needed ]} but are generally office of "bare metal" programming (programming that'due south independent of any operating system such as most embedded programming). With few exceptions, implementations include low-level I/O.

Language tools

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

Automated source code checking and auditing are beneficial in whatsoever language, and for C many such tools exist, such as Lint. A mutual do is to apply Lint to discover questionable code when a programme is first written. One time a program passes Lint, it is then compiled using the C compiler. Also, many compilers tin can optionally warn well-nigh syntactically valid constructs that are probable to actually exist errors. MISRA C is a proprietary set up of guidelines to avoid such questionable lawmaking, adult for embedded systems.^[37]

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

Tools such equally Purify or Valgrind and linking with libraries containing special versions of the memory allocation functions tin help uncover runtime errors in memory usage.

Uses

The C Programming Language

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

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

A consequence of C's wide availability and efficiency is that compilers, libraries and interpreters of other programming languages are often implemented in C. For instance, the reference implementations of Python, Perl, Reddish, and PHP are written in C.

C enables programmers to create efficient implementations of algorithms and data structures, because the layer of abstraction from hardware is sparse, and its overhead is low, an important benchmark 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 approach may be used for portability or convenience; by using C as an intermediate language, additional machine-specific lawmaking 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. Notwithstanding, some of C's shortcomings have prompted the development of other C-based languages specifically designed for use equally intermediate languages, such equally C--.

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

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

C has both directly 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 almost pervasive influence has been syntactical; all of the languages mentioned combine the statement and (more than or less recognizably) expression syntax of C with blazon systems, information models, and/or large-scale plan structures that differ from those of C, sometimes radically.

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

When object-oriented programming languages became popular, C++ and Objective-C were ii 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 then 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-similar syntax.^[44] C++ adds greater typing strength, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Almost a superset of C, C++ now supports most of C, with a few exceptions.

Objective-C was originally a very "sparse" layer on meridian 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 function 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 instance lawmaking will compile on most modernistic compilers that are non in strict standard compliance mode, only information technology does non fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic message be produced.
^ The principal function actually has two arguments, int argc and char *argv[], respectively, which tin can be used to handle command line arguments. The ISO C standard (department v.ane.ii.2.one) requires both forms of main to be supported, which is special treatment not afforded to any other function.

References

^ ^a ^b Kernighan, Brian W.; Ritchie, Dennis M. (Feb 1978). The C Programming Linguistic communication (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110163-0.
^ Ritchie (1993): "Thompson had made a brief effort to produce a system coded in an early version of C—before structures—in 1972, merely gave upward the endeavour."
^ Fruderica (Dec 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 non, perhaps, sally in a class that Algol's adherents would approve of."
^ Band Team (October 23, 2021). "The Ring programming language and other languages". ring-lang.net.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Research Schoolhouse of Computer science at the Australian National University. June 3, 2010. Archived from the original (PDF) on Nov 6, 2013. Retrieved August nineteen, 2013. 1980s: ; Verilog beginning introduced ; Verilog inspired by the C programming language
^ ^a ^b ^c ^d ^e Ritchie (1993)
^ "Programming Linguistic communication Popularity". 2009. Archived from the original on Jan sixteen, 2009. Retrieved January 16, 2009.
^ "TIOBE Programming Community Index". 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 Oct seven, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on December 12, 2019. Retrieved September x, 2019.
^ ^a ^b Johnson, S. C.; Ritchie, D. Thousand. (1978). "Portability of C Programs and the UNIX System". Bell System Tech. J. 57 (6): 2021–2048. CiteSeerX10.1.one.138.35. doi:10.1002/j.1538-7305.1978.tb02141.x. S2CID 17510065. (Note: The PDF is an OCR scan of the original, and contains a rendering of "IBM 370" every bit "IBM 310".)
^ McIlroy, K. D. (1987). A Enquiry Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical study). CSTR. Bell Labs. p. 10. 139. Archived (PDF) from the original on November 11, 2017. Retrieved February 1, 2015.
^ "C transmission pages". FreeBSD Miscellaneous Information Manual (FreeBSD 13.0 ed.). May xxx, 2011. Archived from the original on January 21, 2021. Retrieved January xv, 2021. [1] Archived January 21, 2021, at the Wayback Auto
^ Kernighan, Brian W.; Ritchie, Dennis Grand. (March 1988). The C Programming Language (2nd ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110362-vii.
^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Study). AT&T Labs. Archived (PDF) from the original on Baronial 24, 2014. Retrieved April fourteen, 2014.
^ C Integrity. International Organization 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 August 2, 2013. Retrieved September 7, 2013.
^ "Revised C23 Schedule WG 14 N 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October 10, 2021.
^ "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. ISBN978-0-13-089592-9. Contains a BNF grammer 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 Dec 22, 2017. Retrieved September sixteen, 2011.
^ Kernighan & Ritchie (1996), pp. 192, 259.
^ "10 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 (3rd ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-1-58961-237-ii. Archived from the original on July 29, 2020. Retrieved February 10, 2012.
^ Kernighan & Ritchie (1978), p. half dozen.
^ ^a ^b ^c ^d ^e ^f ^thou Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-ane-4493-2714-9.
^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparison of the Programming Languages C and Pascal". ACM Calculating Surveys. 14 (1): 73–92. doi:10.1145/356869.356872. S2CID 3136859.
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^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January 7, 2007. Retrieved August 5, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-EDUCATION PUBLIC COMPANY Express. pp. 225–230. ISBN978-616-08-2740-four.
^ Raymond, Eric Due south. (October eleven, 1996). The New Hacker'due south Lexicon (3rd ed.). MIT Printing. p. 432. ISBN978-0-262-68092-ix. Archived from the original on November 12, 2012. Retrieved Baronial 5, 2012.
^ "Man Page for lint (freebsd Section 1)". unix.com. May 24, 2001. Retrieved July 15, 2014.
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Sources

Ritchie, Dennis G. (March 1993). "The Development of the C Language". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:ten.1145/155360.155580.
Ritchie, Dennis M. (1993). "The Development of the C Language". The Second ACM SIGPLAN Conference on History of Programming Languages (HOPL-II). ACM. pp. 201–208. doi:10.1145/154766.155580. ISBN0-89791-570-4 . Retrieved November 4, 2014.
Kernighan, Brian Due west.; Ritchie, Dennis K. (1996). The C Programming Language (2d ed.). Prentice Hall. ISBN7-302-02412-Ten.

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). (3.61 MB)
comp.lang.c Oft Asked Questions
A History of C, by Dennis Ritchie

This page was last edited on ane March 2022, at 08:47

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