C# Split String by Comma Reading From a File Msdn

General-purpose programming language

C
Major implementations
The C Programming Linguistic communication ^[1] (oft referred to as One thousand&R), the seminal book on C
Epitome	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)
First appeared	1972; 50 years ago (1972) ^[2]

Stable release	C17 / June 2018; iii years agone (2018-06)
Preview release	C2x (N2731) / Oct 18, 2021; iv months ago (2021-10-18) ^[three]

Typing discipline	Static, weak, manifest, nominal
Bone	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, Split-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, Become, Java, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Pike, Processing, Python, Ring,^[5]Rust, Seed7, Vala, Verilog (HDL),^[vi] Nim, Zig
C Programming at Wikibooks

C (, as in the letter c) is a general-purpose, procedural reckoner programming language supporting structured programming, lexical variable scope, and recursion, with a static type organisation. Past blueprint, C provides constructs that map efficiently to typical machine instructions. Information technology has found lasting utilize in applications previously coded in assembly language. Such applications include operating systems and various application software for computer architectures that range from supercomputers to PLCs and embedded systems.

A successor to the programming linguistic communication B, C was originally developed at Bell Labs by Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. It was practical to re-implementing the kernel of the Unix operating organisation.^[7] During the 1980s, C gradually gained popularity. It has become ane of the almost widely used programming languages,^[8] ^[ix] with C compilers from various vendors bachelor for the bulk of existing computer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and past the International Organization for Standardization (ISO).

C is an imperative procedural linguistic communication. 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 support. Despite its depression-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C plan written with portability in mind can be compiled for a wide variety of estimator platforms and operating systems with few changes to its source code.^[10]

Since 2000, C has consistently ranked amongst the acme two languages in the TIOBE index, a measure of the popularity of programming languages.^[xi]

Overview [edit]

Similar most procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type system prevents unintended operations. In C, all executable code is contained inside subroutines (likewise called "functions", though not strictly in the sense of functional programming). Part parameters are always passed past value (except arrays). Laissez passer-by-reference is false in C by explicitly passing pointer values. C programme source text is free-format, using the semicolon equally a argument terminator and curly braces for grouping blocks of statements.

The C linguistic communication also exhibits the following characteristics:

The language has a pocket-sized, fixed number of keywords, including a full set of control catamenia 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 arithmetics, bitwise, and logic operators: +,+=,++,&,||, etc.
More i assignment may be performed in a single statement.
Functions:
- Function return values can be ignored, when not needed.
- Function and data pointers allow advertisement hoc run-fourth dimension polymorphism.
- Functions may not be divers within the lexical scope of other functions.
Data typing is static, only weakly enforced; all data has a type, but implicit conversions are possible.
Declaration syntax mimics usage context. C has no "define" keyword; instead, a statement outset with the proper name of a type is taken equally a proclamation. There is no "function" keyword; instead, a function is indicated by the presence of a parenthesized argument list.
User-defined (typedef) and compound types are possible.
- Heterogeneous aggregate data types (struct) allow related data elements to be accessed and assigned as a unit.
- Marriage is a structure with overlapping members; only the last fellow member stored is valid.
- Assortment indexing is a secondary notation, defined in terms of pointer arithmetic. Dissimilar structs, arrays are not first-class objects: they cannot be assigned or compared using single built-in operators. At that place is no "array" keyword in apply or definition; instead, foursquare brackets bespeak arrays syntactically, for example calendar month[xi].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are not a singled-out information type, but are conventionally implemented as aught-terminated character arrays.
Depression-level admission to computer memory is possible by converting car addresses to typed pointers.
Procedures (subroutines not returning values) are a special case of role, with an untyped return type void.
A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
There is a basic form of modularity: files 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.
Circuitous functionality such every bit I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does not include certain features constitute in other languages (such equally object orientation and garbage collection), these can exist implemented or emulated, oft through the employ of external libraries (east.thou., the GLib Object System or the Boehm garbage collector).

Relations to other languages [edit]

Many after languages accept borrowed directly or indirectly from C, including C++, C#, Unix'south C shell, D, Go, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[six] These languages accept drawn many of their control structures and other basic features from C. About of them (Python existence a dramatic exception) also 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 tin can be radically different.

History [edit]

Early developments [edit]

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 system, originally implemented in assembly language on a PDP-7 by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Eventually, they decided to port the operating system to a PDP-11. The original PDP-eleven version of Unix was also developed in assembly language.^[7]

Thompson desired a programming language to make utilities for the new platform. At first, he tried to brand a Fortran compiler, but soon gave up the idea. Instead, he created a cut-down version of the recently developed BCPL systems programming linguistic communication. The official description of BCPL was not available at the fourth dimension,^[12] and Thompson modified the syntax to be less wordy, producing the similar only somewhat simpler B.^[7] However, few utilities were ultimately written in B considering it was too irksome, and B could not take advantage of PDP-xi features such as byte addressability.

In 1972, Ritchie started to improve B, virtually notably calculation information typing for variables, which resulted in creating a new language C.^[13] The C compiler and some utilities made with it were included in Version 2 Unix.^[14]

At Version 4 Unix, released in Nov 1973, the Unix kernel was extensively re-implemented in C.^[7] By this fourth dimension, the C linguistic communication had caused some powerful features such equally struct types.

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

Unix was i of the first operating organization kernels implemented in a language other than assembly. Earlier instances include the Multics system (which was written in PL/I) and Primary Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In around 1977, Ritchie and Stephen C. Johnson fabricated farther changes to the language to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served as the ground for several implementations of C on new platforms.^[13]

K&R C [edit]

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

K&R introduced several language features:

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

Even afterward the publication of the 1989 ANSI standard, for many years Chiliad&R C was nonetheless considered the "lowest common denominator" to which C programmers restricted themselves when maximum portability was desired, since many older compilers were withal in use, and because carefully written Thousand&R C code can be legal Standard C as well.

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

For example:

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

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

Since Grand&R part declarations did not include whatsoever information nigh office arguments, function parameter type checks were not performed, although some compilers would issue a warning message if a local role was chosen with the incorrect number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Separate tools such equally Unix's lint utility were developed that (amidst other things) could check for consistency of office utilize across multiple source files.

In the years following the publication of One thousand&R C, several features were added to the linguistic communication, supported past compilers from AT&T (in particular 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 big number of extensions and lack of agreement on a standard library, together with the language 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 [edit]

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

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

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

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

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

C89 is supported by current C compilers, and virtually modern C code is based on information technology. Any program written just in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, inside its resource limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the employ of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such every bit the exact size of information types and byte endianness.

In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to divide the code into Standard and K&R sections to prevent the use on a M&R C-based compiler of features available only in Standard C.

After the ANSI/ISO standardization procedure, the C language specification remained relatively static for several years. In 1995, Normative Subpoena 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally every bit C95) was published, to correct some details and to add more all-encompassing support for international character sets.^[18]

C99 [edit]

The C standard was farther revised in the belatedly 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 data types (including long long int and a circuitous blazon to represent circuitous numbers), variable-length arrays and flexible assortment members, improved support for IEEE 754 floating point, support 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 equally extensions in several C compilers.

C99 is for the nearly part backward compatible with C90, but is stricter in some means; in item, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 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++, however, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.^[twenty] ^{[ needs update ]}

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

C11 [edit]

In 2007, 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 past existing implementations.

The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and premises-checked functions. It besides makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__ is defined as 201112L to indicate that C11 support is bachelor.

C17 [edit]

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

C2x [edit]

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

Embedded C [edit]

Historically, embedded C programming requires nonstandard extensions to the C language in order to support exotic features such equally fixed-indicate arithmetic, multiple singled-out memory banks, and bones I/O operations.

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

Syntax [edit]

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

C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either ascertain new types using keywords such as struct, union, and enum, or assign types to and perchance reserve storage for new variables, usually by writing the type followed by the variable name. 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 telescopic of declarations and to deed as a single statement for control structures.

As an imperative language, C uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; every bit a side effect of the evaluation, functions may be chosen and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several command-menstruation statements identified by reserved keywords. Structured programming is supported by if … [else] conditional execution and by do … while, while, and for iterative execution (looping). The for statement has split initialization, testing, and reinitialization expressions, whatsoever or all of which can be omitted. suspension and continue can be used to exit the innermost enclosing loop statement or skip to its reinitialization. At that place is also a non-structured goto statement which branches straight to the designated characterization within the office. switch selects a case to be executed based on the value of an integer expression.

Expressions can use a diverseness of built-in operators and may contain function calls. The club in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. Yet, all side effects (including storage to variables) volition occur before the next "sequence bespeak"; sequence points include the finish of each expression argument, and the entry to and render from each function call. Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a loftier degree of object lawmaking optimization past the compiler, merely requires C programmers to take more care to obtain reliable results than is needed for other programming languages.

Kernighan and Ritchie say in the Introduction of The C Programming Language: "C, similar any other linguistic communication, has its blemishes. Some of the operators have the incorrect precedence; some parts of the syntax could be amend."^[25] The C standard did not attempt to correct many of these blemishes, considering of the impact of such changes on already existing software.

Character set [edit]

The bones C source graphic symbol fix includes the following characters:

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

Newline indicates the terminate of a text line; information technology demand not correspond to an actual unmarried character, although for convenience C treats it as ane.

Boosted multi-byte encoded characters may be used in string literals, simply 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 character), although this feature is not nonetheless widely implemented.

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

Reserved words [edit]

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

auto
intermission
example
char
const
keep
default
do
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 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 begin with an underscore followed by a upper-case letter letter, because identifiers of that form were previously reserved by the C standard for use only by implementations. Since existing programme source code should not have been using these identifiers, information technology would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers practise define more than convenient synonyms for underscored identifiers. The language previously included a reserved word called entry, merely this was seldom implemented, and has now been removed as a reserved give-and-take.^[27]

Operators [edit]

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

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

C uses the operator = (used in mathematics to express equality) to indicate consignment, post-obit the precedent of Fortran and PL/I, only unlike ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these 2 operators (assignment and equality) may result in the adventitious use of one in place of the other, and in many cases, the fault does not produce an fault message (although some compilers produce warnings). For instance, the provisional expression if (a == b + 1) might mistakenly exist written equally if (a = b + one), which will be evaluated equally true if a is not zero later the assignment.^[28]

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

"Hi, earth" example [edit]

The "hello, world" example, which appeared in the start edition of Grand&R, has go the model for an introductory program in about programming textbooks. The programme prints "hello, world" to the standard output, which is usually a terminal or screen display.

The original version was:^[30]

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

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

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

The get-go line of the program 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 proper noun, as opposed to double quotes which typically include local or projection-specific header files.

The next line indicates that a function named main is beingness defined. The principal function serves a special purpose in C programs; the run-time environment calls the main function to begin program execution. The type specifier int indicates that the value that is returned to the invoker (in this instance the run-fourth dimension environs) equally a outcome of evaluating the principal role, is an integer. The keyword void equally a parameter list indicates that this role takes no arguments.^[b]

The opening curly brace indicates the outset 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 statement, the address of the first character in the string literal "hullo, earth\n". The cord literal is an unnamed array with elements of blazon char, ready automatically past the compiler with a final 0-valued grapheme to marker the cease of the array (printf needs to know this). The \northward is an escape sequence that C translates to a newline character, which on output signifies the finish of the current line. The return value of the printf function is of blazon int, only it is silently discarded since it is non used. (A more careful programme might examination the render value to decide whether or not the printf role succeeded.) The semicolon ; terminates the statement.

The closing curly caryatid indicates the cease of the lawmaking for the chief role. According to the C99 specification and newer, the chief role, unlike whatever other role, will implicitly render a value of 0 upon reaching the } that terminates the function. (Formerly an explicit return 0; statement was required.) This is interpreted by the run-time system as an exit lawmaking indicating successful execution.^[31]

Data types [edit]

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

C is often used in low-level systems programming where escapes from the type organization may be necessary. The compiler attempts to ensure type definiteness of most expressions, simply the programmer can override the checks in diverse ways, either past using a type cast to explicitly convert a value from one type to some other, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way.

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

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

Pointers [edit]

C supports the utilize of pointers, a type of reference that records the accost or location of an object or function in memory. Pointers can be dereferenced to admission data stored at the address pointed to, or to invoke a pointed-to role. Pointers can be manipulated using assignment or pointer arithmetic. The run-fourth dimension representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-within-word field), but since a pointer's type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile fourth dimension. 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 memory allocation is performed using pointers. Many data types, such every bit trees, are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to college-society functions (such as qsort or bsearch) or equally callbacks to be invoked by issue handlers.^[31]

A null pointer value explicitly points to no valid location. Dereferencing a aught pointer value is undefined, oft resulting in a segmentation error. Null pointer values are useful for indicating special cases such equally no "next" arrow in the final node of a linked list, or every bit an error indication from functions returning pointers. In advisable contexts in source code, such as for assigning to a pointer variable, a nix pointer constant tin be written every bit 0, with or without explicit casting to a pointer type, or as the Nix macro defined by several standard headers. In conditional contexts, aught pointer values evaluate to false, while all other arrow values evaluate to true.

Void pointers (void *) point to objects of unspecified type, and can therefore be used equally "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 tin can hands be (and in many contexts implicitly are) converted to and from any other object pointer type.^[31]

Careless use of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable tin be made to point to whatsoever capricious location, which tin can cause undesirable effects. Although properly used pointers point to safety places, they can be made to point to dangerous places by using invalid pointer arithmetic; the objects they point to may proceed to exist used afterwards deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may be direct assigned an unsafe value using a bandage, union, or through some other 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 accost these issues by using more restrictive reference types.

Arrays [edit]

Array types in C are traditionally of a fixed, static size specified at compile time. The more contempo C99 standard as well allows a form of variable-length arrays. Still, it is also possible to allocate a cake of memory (of arbitrary size) at run-time, using the standard library'due south malloc function, and treat it as an assortment.

Since arrays are always accessed (in effect) via pointers, array accesses are typically not checked confronting the underlying assortment size, although some compilers may provide bounds checking as an option.^[34] ^[35] Array bounds violations are therefore possible and can lead to various repercussions, including illegal memory accesses, abuse of information, buffer overruns, and run-fourth dimension exceptions.

C does not have a special provision for declaring multi-dimensional arrays, but rather relies on recursion within the type organisation to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multi-dimensional array" tin can exist thought of as increasing in row-major order. Multi-dimensional arrays are commonly used in numerical algorithms (mainly from practical linear algebra) to store matrices. The structure of the C array is well suited to this particular job. All the same, in early versions of C the bounds of the array must be known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this was to allocate the array with an boosted "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which accost this consequence.

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

                        int                                    func            (            int                                    N            ,                                    int                                    M            )                        {                                                bladder                                    (            *            p            )[            N            ][            M            ]                                    =                                    malloc            (            sizeof                                    *            p            );                                                if                                    (            !            p            )                                                render                                    -i            ;                                                for                                    (            int                                    i                                    =                                    0            ;                                    i                                    <                                    Northward            ;                                    i            ++            )                                                for                                    (            int                                    j                                    =                                    0            ;                                    j                                    <                                    1000            ;                                    j            ++            )                                                (            *            p            )[            i            ][            j            ]                                    =                                    i                                    +                                    j            ;                                                print_array            (            N            ,                                    M            ,                                    p            );                                                free            (            p            );                                                render                                    one            ;                        }

Array–arrow interchangeability [edit]

The subscript notation x[i] (where x designates a pointer) is syntactic sugar for *(x+i).^[36] Taking reward of the compiler'due south knowledge of the arrow blazon, the accost that x + i points to is not the base address (pointed to by 10) incremented by i bytes, merely rather is defined to be the base address incremented by i multiplied by the size of an element that x points to. Thus, ten[i] designates the i+ith element of the array.

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

The total size of an array ten can be adamant by applying sizeof to an expression of array type. The size of an chemical element can exist determined past applying the operator sizeof to any dereferenced element of an array A, as in n = sizeof A[0]. This, the number of elements in a declared array A can be adamant as sizeof A / sizeof A[0]. Note, that if just a pointer to the first element is available equally it is often the instance in C code because of the automated conversion described above, the information virtually the full type of the assortment and its length are lost.

Memory management [edit]

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

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

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

Where possible, automatic or static allotment is usually simplest because the storage is managed past the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. Yet, many information structures tin can alter 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 common example of this. (Encounter the commodity on malloc for an example of dynamically allocated arrays.) Unlike automatic allocation, which can neglect at run time with uncontrolled consequences, the dynamic allotment functions return an indication (in the form of a goose egg arrow value) when the required storage cannot be allocated. (Static resource allotment that is too large is usually detected by the linker or loader, earlier the program can even begin execution.)

Unless otherwise specified, static objects contain nothing or zippo pointer values upon program startup. Automatically and dynamically allocated objects are initialized just if an initial value is explicitly specified; otherwise they initially take indeterminate values (typically, whatever scrap design happens to exist present in the storage, which might non even represent a valid value for that blazon). If the programme attempts to admission an uninitialized value, the results are undefined. Many modernistic compilers try to discover and warn well-nigh this problem, but both faux positives and false negatives tin can occur.

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

Libraries [edit]

The C programming 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 within the library that may exist used by a program, and declarations of special data types and macro symbols used with these functions. In order for a plan to utilize a library, it must include the library's header file, and the library must be linked with the program, which in many cases requires compiler flags (e.g., -lm, shorthand for "link the math library").^[31]

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

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

Since many programs take 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 can be used from higher-level languages similar Java, Perl, and Python.^[31]

File treatment and streams [edit]

File input and output (I/O) is not part of the C linguistic communication itself only instead is handled past libraries (such as the C standard library) and their associated header files (e.g. stdio.h). File handling is more often than not implemented through high-level I/O which works through streams. A stream is from this perspective a data flow that is contained 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 retentiveness expanse or queue) is temporarily used to store data earlier information technology's sent to the terminal destination. This reduces the time spent waiting for slower devices, for example a hard drive or solid state drive. Low-level I/O functions are not part of the standard C library^{[ clarification needed ]} but are generally role of "bare metallic" programming (programming that's independent of any operating organisation such as most embedded programming). With few exceptions, implementations include depression-level I/O.

Linguistic communication tools [edit]

A number of tools have been adult to assistance C programmers notice and fix statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided past the compiler. The tool lint was the offset such, leading to many others.

Automated source lawmaking checking and auditing are beneficial in any linguistic communication, and for C many such tools exist, such every bit Lint. A mutual practice is to use Lint to detect questionable code when a program is get-go written. Once a plan passes Lint, it 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 gear up of guidelines to avert such questionable code, developed for embedded systems.^[37]

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

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

Uses [edit]

The C Programming Linguistic communication

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

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

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

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

C is sometimes used every bit an intermediate language by implementations of other languages. This approach may be used for portability or convenience; by using C as an intermediate linguistic communication, boosted machine-specific code generators are not necessary. C has some features, such as line-number preprocessor directives and optional superfluous commas at the finish of initializer lists, that support compilation of generated code. Still, some of C'south shortcomings take prompted the evolution of other C-based languages specifically designed for use every bit intermediate languages, such as C--.

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

[edit]

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

C has both directly and indirectly influenced many afterwards languages such as C#, D, Go, Java, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix's C crush.^[42] The nearly pervasive influence has been syntactical; all of the languages mentioned combine the argument and (more than or less recognizably) expression syntax of C with blazon systems, data models, and/or large-scale program structures that differ from those of C, sometimes radically.

Several C or near-C interpreters exist, including Ch and CINT, which tin can likewise 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 by Bjarne Stroustrup as an approach to providing object-oriented functionality with a C-like syntax.^[44] C++ adds greater typing strength, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Nigh 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 [edit]

^ The original case lawmaking will compile on most modern compilers that are not in strict standard compliance mode, but it does non fully adjust to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic message be produced.
^ The main function actually has two arguments, int argc and char *argv[], respectively, which can exist used to handle command line arguments. The ISO C standard (department five.ane.ii.2.1) requires both forms of primary to be supported, which is special handling not afforded to whatever other function.

References [edit]

^ ^a ^b Kernighan, Brian Westward.; 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 try to produce a system coded in an early version of C—earlier structures—in 1972, but gave up the endeavor."
^ Fruderica (December 13, 2020). "History of C". The cppreference.com. Archived from the original on October 24, 2020. Retrieved Oct 24, 2020.
^ Ritchie (1993): "The scheme of blazon composition adopted by C owes considerable debt to Algol 68, although it did non, perhaps, emerge in a class that Algol's adherents would approve of."
^ Ring Team (October 23, 2021). "The Ring programming language and other languages". ring-lang.net.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Inquiry School of Computer science at the Australian National University. June 3, 2010. Archived from the original (PDF) on Nov half-dozen, 2013. Retrieved August 19, 2013. 1980s: ; Verilog first introduced ; Verilog inspired by the C programming language
^ ^a ^b ^c ^d ^east Ritchie (1993)
^ "Programming Language Popularity". 2009. Archived from the original on Jan xvi, 2009. Retrieved January xvi, 2009.
^ "TIOBE Programming Customs 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 7, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on Dec 12, 2019. Retrieved September ten, 2019.
^ ^a ^b Johnson, Due south. C.; Ritchie, D. Yard. (1978). "Portability of C Programs and the UNIX Organisation". Bell Arrangement Tech. J. 57 (6): 2021–2048. CiteSeerXten.1.1.138.35. doi:10.1002/j.1538-7305.1978.tb02141.10. S2CID 17510065. (Note: The PDF is an OCR browse of the original, and contains a rendering of "IBM 370" every bit "IBM 310".)
^ McIlroy, M. D. (1987). A Enquiry Unix reader: annotated excerpts from the Programmer's Transmission, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. p. 10. 139. Archived (PDF) from the original on Nov xi, 2017. Retrieved Feb 1, 2015.
^ "C manual pages". FreeBSD Miscellaneous Information Manual (FreeBSD 13.0 ed.). May 30, 2011. Archived from the original on January 21, 2021. Retrieved January 15, 2021. [one] Archived January 21, 2021, at the Wayback Auto
^ Kernighan, Brian W.; Ritchie, Dennis M. (March 1988). The C Programming Language (second ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-xiii-110362-vii.
^ 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". Abode page. ISO/IEC. Archived from the original on February 12, 2018. Retrieved June 2, 2011.
^ Andrew Binstock (Oct 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on August 2, 2013. Retrieved September vii, 2013.
^ "Revised C23 Schedule WG fourteen 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 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. 3.
^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on December 22, 2017. Retrieved September 16, 2011.
^ Kernighan & Ritchie (1996), pp. 192, 259.
^ "10 Mutual 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 (third ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-ane-58961-237-two. Archived from the original on July 29, 2020. Retrieved Feb 10, 2012.
^ Kernighan & Ritchie (1978), p. vi.
^ ^a ^b ^c ^d ^e ^f ^grand Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-1-4493-2714-ix.
^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparing of the Programming Languages C and Pascal". ACM Computing Surveys. fourteen (ane): 73–92. doi:ten.1145/356869.356872. S2CID 3136859.
^ Kernighan & Ritchie (1996), p. 122.
^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January 7, 2007. Retrieved August 5, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-EDUCATION PUBLIC COMPANY Express. pp. 225–230. ISBN978-616-08-2740-4.
^ Raymond, Eric South. (October 11, 1996). The New Hacker'due south Dictionary (3rd ed.). MIT Printing. p. 432. ISBN978-0-262-68092-9. Archived from the original on November 12, 2012. Retrieved August 5, 2012.
^ "Man Page for lint (freebsd Section 1)". unix.com. May 24, 2001. Retrieved July xv, 2014.
^ Dale, Nell B.; Weems, Chip (2014). Programming and trouble solving with C++ (6th ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
^ Dr. Dobb's Sourcebook. United statesA.: Miller Freeman, Inc. November–December 1995.
^ "Using C for CGI Programming". linuxjournal.com. March i, 2005. Archived from the original on Feb 13, 2010. Retrieved January four, 2010.
^ McMillan, Robert (August 1, 2013). "Is Java Losing Its Mojo?". Wired. Archived from the original on February 15, 2017. Retrieved March 5, 2017.
^ O'Regan, Gerard (September 24, 2015). Pillars of computing : a compendium of select, pivotal technology firms. ISBN978-3319214641. OCLC 922324121.
^ Rauchwerger, Lawrence (2004). Languages and compilers for parallel computing : 16th international workshop, LCPC 2003, Higher Station, TX, USA, Oct two-4, 2003 : revised papers. Springer. ISBN978-3540246442. OCLC 57965544.
^ Stroustrup, Bjarne (1993). "A History of C++: 1979−1991" (PDF). Archived (PDF) from the original on February 2, 2019. Retrieved June 9, 2011.

Sources [edit]

Ritchie, Dennis M. (March 1993). "The Development of the C Linguistic communication". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:ten.1145/155360.155580.
Ritchie, Dennis Grand. (1993). "The Evolution of the C Language". The Second ACM SIGPLAN Briefing on History of Programming Languages (HOPL-Ii). ACM. pp. 201–208. doi:10.1145/154766.155580. ISBN0-89791-570-four . Retrieved Nov 4, 2014.
Kernighan, Brian W.; Ritchie, Dennis One thousand. (1996). The C Programming Language (2nd ed.). Prentice Hall. ISBN7-302-02412-X.

External links [edit]

ISO C Working Group official website
- ISO/IEC 9899, publicly available official C documents, including the C99 Rationale
- "C99 with Technical corrigenda TC1, TC2, and TC3 included" (PDF). (3.61 MB)
comp.lang.c Ofttimes Asked Questions
A History of C, by Dennis Ritchie

ingramdonly1990.blogspot.com

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