C# Handle Api Down Try Again

General-purpose programming linguistic communication

C
Major implementations
The C Programming Linguistic communication ^[1] (ofttimes referred to as K&R), the seminal volume on C
Epitome	Multi-paradigm: imperative (procedural), structured
Designed past	Dennis Ritchie
Developer	Dennis Ritchie & Bell Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
First appeared	1972; l years ago (1972) ^[2]

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

Typing discipline	Static, weak, manifest, nominal
OS	Cross-platform
Filename extensions	.c, .h
Website	www.iso.org/standard/74528.html world wide web.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 past
B (BCPL, CPL), ALGOL 68,^[4] assembly, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Get, Java, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Pike, Processing, Python, Ring,^[v]Rust, Seed7, Vala, Verilog (HDL),^[6] Nim, Zig
C Programming at Wikibooks

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

A successor to the programming linguistic communication B, C was originally adult at Bong Labs by Dennis Ritchie betwixt 1972 and 1973 to construct utilities running on Unix. It was practical to re-implementing the kernel of the Unix operating arrangement.^[7] During the 1980s, C gradually gained popularity. Information technology has become one of the most widely used programming languages,^[8] ^[9] with C compilers from various vendors bachelor for the majority of existing computer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and past the International Arrangement for Standardization (ISO).

C is an imperative procedural language. It was designed to exist compiled to provide depression-level admission to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C program written with portability in heed tin 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 among the top 2 languages in the TIOBE index, a mensurate of the popularity of programming languages.^[11]

Overview [edit]

Like most procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type system prevents unintended operations. In C, all executable code is contained within subroutines (also called "functions", though not strictly in the sense of functional programming). Part parameters are ever passed by value (except arrays). Pass-by-reference is simulated in C by explicitly passing pointer values. C program source text is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements.

The C language also exhibits the following characteristics:

The linguistic communication has a pocket-sized, fixed number of keywords, including a total set of control flow primitives: if/else, for, exercise/while, while, and switch. User-defined names are not distinguished from keywords by any kind of sigil.
It has a large number of arithmetic, bitwise, and logic operators: +,+=,++,&,||, etc.
More than 1 assignment may be performed in a single statement.
Functions:
- Part render values tin be ignored, when non needed.
- Function and data pointers permit advertising hoc run-time polymorphism.
- Functions may non be divers inside the lexical scope of other functions.
Data typing is static, but weakly enforced; all data has a blazon, but implicit conversions are possible.
Declaration syntax mimics usage context. C has no "define" keyword; instead, a statement beginning with the name of a type is taken equally a announcement. There is no "role" keyword; instead, a role is indicated by the presence of a parenthesized argument listing.
User-defined (typedef) and compound types are possible.
- Heterogeneous amass information types (struct) allow related information elements to exist accessed and assigned equally a unit of measurement.
- Union is a structure with overlapping members; only the concluding member stored is valid.
- Assortment indexing is a secondary note, defined in terms of pointer arithmetic. Unlike structs, arrays are non kickoff-grade objects: they cannot be assigned or compared using single built-in operators. There is no "array" keyword in apply 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 non a distinct data type, merely are conventionally implemented as zip-terminated graphic symbol arrays.
Low-level access to computer memory is possible past converting car addresses to typed pointers.
Procedures (subroutines non returning values) are a special case of function, with an untyped return blazon void.
A preprocessor performs macro definition, source code file inclusion, and provisional compilation.
In that location is a basic course of modularity: files tin exist 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 as 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 as object orientation and garbage collection), these can be implemented or emulated, often through the use of external libraries (e.k., the GLib Object System or the Boehm garbage collector).

Relations to other languages [edit]

Many later on languages have borrowed directly or indirectly from C, including C++, C#, Unix'due south C shell, D, Go, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Reddish, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[vi] These languages have fatigued many of their control structures and other bones features from C. Most of them (Python existence a dramatic exception) also express highly similar syntax to C, and they tend to combine the recognizable expression and argument syntax of C with underlying type systems, data models, and semantics that can be radically dissimilar.

History [edit]

Early developments [edit]

Timeline of linguistic communication evolution
Year	C Standard^[10]
1972	Birth
1978	Thou&R C
1989/1990	ANSI C and ISO C
1999	C99
2011	C11
2017	C17
TBD	C2x

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

Thompson desired a programming linguistic communication to make utilities for the new platform. At first, he tried to make a Fortran compiler, only soon gave upwards 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 time,^[12] and Thompson modified the syntax to be less wordy, producing the similar merely somewhat simpler B.^[seven] Still, few utilities were ultimately written in B because it was too tedious, and B could not have advantage of PDP-11 features such equally byte addressability.

In 1972, Ritchie started to improve B, well-nigh notably adding data typing for variables, which resulted in creating a new language C.^[xiii] The C compiler and some utilities made with it were included in Version 2 Unix.^[14]

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

The preprocessor was introduced around 1973 at the urging of Alan Snyder and also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I. Its original version provided merely included files and simple cord replacements: #include and #ascertain of parameterless macros. Soon after that, it was extended, mostly by Mike Lesk and then by John Reiser, to incorporate macros with arguments and provisional compilation.^[vii]

Unix was i of the offset operating system kernels implemented in a language other than assembly. Earlier instances include the Multics system (which was written in PL/I) and Master Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating organization. Johnson'due south Portable C Compiler served every bit the basis for several implementations of C on new platforms.^[13]

One thousand&R C [edit]

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language.^[one] This volume, known to C programmers as K&R, served for many years as an breezy 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 too referred to as C78.^[fifteen] The 2d edition of the book^[16] covers the later ANSI C standard, described beneath.

Yard&R introduced several linguistic communication features:

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

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

In early versions of C, only functions that return types other than int must exist declared if used before the role definition; functions used without prior annunciation 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                                    >                                    1            )                                                test2                                    =                                    0            ;                                                else                                                test2                                    =                                    other_function            ();                                                return                                    test2            ;                        }

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

Since K&R part declarations did not include any information nigh part arguments, office parameter type checks were not performed, although some compilers would consequence a warning bulletin if a local function was called with the incorrect number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Split tools such equally Unix'southward lint utility were developed that (among other things) could check for consistency of role use across multiple source files.

In the years post-obit the publication of K&R C, several features were added to the language, supported by compilers from AT&T (in item 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 linguistic communication popularity and the fact that not fifty-fifty the Unix compilers precisely implemented the G&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 Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; nonetheless, 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 as ANSI X3.159-1989 "Programming Language C". This version of the language is frequently 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) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language.

ANSI, like other national standards bodies, no longer develops the C standard independently, simply 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 Thou&R C, incorporating many of the afterward introduced unofficial features. The standards committee also included several boosted features such every bit function prototypes (borrowed from C++), void pointers, support 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 Thou&R interface continued to exist permitted, for compatibility with existing source code.

C89 is supported by current C compilers, and nigh modern C code is based on it. Any programme written simply in Standard C and without any hardware-dependent assumptions will run correctly on whatever platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile but on a sure platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the verbal size of data types and byte endianness.

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

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

C99 [edit]

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

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

C99 is for the nigh function astern compatible with C90, simply is stricter in some means; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is bachelor. GCC, Solaris Studio, and other C compilers now back up many or all of the new features of C99. The C compiler in Microsoft Visual C++, nevertheless, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.^[20] ^{[ needs update ]}

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

C11 [edit]

In 2007, work began on some other revision of the C standard, informally called "C1X" until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested 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 indicate that C11 support is available.

C17 [edit]

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

C2x [edit]

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

Embedded C [edit]

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

In 2008, the C Standards Committee published a technical study extending the C language^[22] to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features non available in normal C, such as fixed-betoken arithmetic, named address spaces, and basic I/O hardware addressing.

Syntax [edit]

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

C source files contain declarations and function definitions. Function definitions, in turn, comprise declarations and statements. Declarations either define new types using keywords such equally struct, spousal relationship, and enum, or assign types to and perhaps reserve storage for new variables, commonly 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 scope of declarations and to deed as a single statement for control structures.

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

Expressions tin can use a diverseness of born operators and may incorporate function calls. The social club in which arguments to functions and operands to well-nigh operators are evaluated is unspecified. The evaluations may even be interleaved. All the same, all side effects (including storage to variables) volition occur earlier the adjacent "sequence point"; sequence points include the stop of each expression statement, and the entry to and return from each function call. Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a high degree of object code optimization by the compiler, but 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, like whatever other linguistic communication, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be amend."^[25] The C standard did not endeavor to correct many of these blemishes, because of the touch of such changes on already existing software.

Grapheme gear up [edit]

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

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

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

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

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

Reserved words [edit]

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

auto
break
case
char
const
continue
default
do
double
else
enum
extern
bladder
for
goto
if
int
long
register
render
short
signed
sizeof
static
struct
switch
typedef
spousal relationship
unsigned
void
volatile
while

C99 reserved 5 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, considering identifiers of that form were previously reserved by the C standard for utilise but past implementations. Since existing program source lawmaking should not have been using these identifiers, it would not be afflicted when C implementations started supporting these extensions to the programming language. Some standard headers do define more than convenient synonyms for underscored identifiers. The linguistic communication previously included a reserved word called entry, but this was seldom implemented, and has now been removed as a reserved discussion.^[27]

Operators [edit]

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

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

C uses the operator = (used in mathematics to express equality) to signal assignment, following the precedent of Fortran and PL/I, just unlike ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these ii operators (assignment and equality) may result in the accidental use of i in place of the other, and in many cases, the mistake does not produce an fault bulletin (although some compilers produce warnings). For example, the conditional expression if (a == b + 1) might mistakenly be written as if (a = b + i), which will be evaluated every bit true if a is not zero after the assignment.^[28]

The C operator precedence is non e'er 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 & one == 0, which must be written every bit (x & 1) == 0 if that is the coder'southward intent.^[29]

"How-do-you-do, world" example [edit]

The "hello, earth" example, which appeared in the first edition of K&R, has get the model for an introductory programme in most programming textbooks. The program prints "hello, earth" to the standard output, which is usually a terminal or screen brandish.

The original version was:^[thirty]

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

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

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

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

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

The opening curly caryatid indicates the beginning of the definition of the primary function.

The adjacent line calls (diverts execution to) a role named printf, which in this example is supplied from a system library. In this phone call, the printf part is passed (provided with) a single argument, the address of the first character in the string literal "hello, world\n". The cord literal is an unnamed array with elements of type char, ready automatically by the compiler with a last 0-valued character to mark the end of the array (printf needs to know this). The \n is an escape sequence that C translates to a newline graphic symbol, which on output signifies the stop of the current line. The render value of the printf function is of blazon int, but information technology is silently discarded since it is not used. (A more careful program might test the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement.

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

Data types [edit]

The blazon arrangement in C is static and weakly typed, which makes it similar to the blazon system of ALGOL descendants such as Pascal.^[32] There are congenital-in types for integers of various sizes, both signed and unsigned, floating-point numbers, and enumerated types (enum). Integer blazon char is oft used for unmarried-byte characters. C99 added a boolean datatype. There are also derived types including arrays, pointers, records (struct), and unions (spousal relationship).

C is oft used in low-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure blazon correctness of well-nigh expressions, but the programmer tin override the checks in various ways, either by using a type bandage to explicitly catechumen a value from 1 type to another, or by using pointers or unions to reinterpret the underlying $.25 of a data object in another mode.

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

C'due south usual arithmetics conversions allow for efficient lawmaking to be generated, merely 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 tin generate unexpected results if the signed value is negative.

Pointers [edit]

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

A nothing arrow value explicitly points to no valid location. Dereferencing a null pointer value is undefined, oft resulting in a division fault. Aught arrow values are useful for indicating special cases such as no "next" pointer 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 aught pointer constant can be written as 0, with or without explicit casting to a pointer blazon, or as the Cipher macro defined past several standard headers. In conditional contexts, null arrow values evaluate to false, while all other pointer values evaluate to true.

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

Devil-may-care utilise of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable can be fabricated to point to whatever arbitrary location, which tin cause undesirable effects. Although properly used pointers point to safe places, they can be made to indicate to unsafe places by using invalid pointer arithmetics; the objects they point to may go along to be used after deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may exist straight assigned an unsafe value using a bandage, matrimony, or through another corrupt pointer. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more than restrictive reference types.

Arrays [edit]

Array types in C are traditionally of a fixed, static size specified at compile fourth dimension. The more than recent C99 standard also allows a class of variable-length arrays. However, it is besides possible to classify a block of retention (of capricious size) at run-time, using the standard library's malloc function, and care for it as an assortment.

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

C does not accept a special provision for declaring multi-dimensional arrays, but rather relies on recursion within the blazon system to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multi-dimensional array" can exist thought of as increasing in row-major club. Multi-dimensional arrays are commonly used in numerical algorithms (mainly from practical linear algebra) to shop matrices. The structure of the C array is well suited to this item task. Withal, in early 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 be 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 modern C (C99 or after) shows allocation of a two-dimensional assortment on the heap and the utilize of multi-dimensional assortment indexing for accesses (which tin use premises-checking on many C compilers):

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

Array–pointer interchangeability [edit]

The subscript note ten[i] (where x designates a pointer) is syntactic sugar for *(x+i).^[36] Taking advantage of the compiler's knowledge of the pointer type, the accost that x + i points to is non the base address (pointed to by 10) incremented by i bytes, just rather is defined to exist the base address incremented by i multiplied by the size of an element that x points to. Thus, x[i] designates the i+aneth element of the array.

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

The total size of an array 10 can be determined by applying sizeof to an expression of array type. The size of an element can exist determined by applying the operator sizeof to any dereferenced element of an array A, as in due north = sizeof A[0]. This, the number of elements in a alleged array A tin can be determined every bit sizeof A / sizeof A[0]. Note, that if merely a pointer to the start chemical element is available as information technology is often the case in C code considering of the automatic conversion described above, the information about the full type of the array and its length are lost.

Memory direction [edit]

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

Static retention allocation: space for the object is provided in the binary at compile-time; these objects have an extent (or lifetime) every bit long as the binary which contains them is loaded into memory.
Automatic memory allocation: temporary objects can exist stored on the stack, and this space is automatically freed and reusable after the cake in which they are declared is exited.
Dynamic memory allocation: blocks of memory of capricious size can be requested at run-time using library functions such as malloc from a region of memory called the heap; these blocks persist until afterward freed for reuse by calling the library office realloc or free

These three approaches are appropriate in different situations and have various trade-offs. For case, static memory allotment has little allocation overhead, automatic allocation may involve slightly more than overhead, and dynamic retentivity allocation tin can potentially have a great deal of overhead for both allotment and deallocation. The persistent nature of static objects is useful for maintaining state information across function calls, automated allotment is easy to utilise merely stack space is typically much more than limited and transient than either static retentivity or heap space, and dynamic memory allocation allows convenient resource allotment of objects whose size is known only at run-time. Most C programs make all-encompassing apply of all three.

Where possible, automatic or static allocation is commonly simplest because the storage is managed by the compiler, freeing the programmer of the potentially error-decumbent chore of manually allocating and releasing storage. All the same, many data structures can change in size at runtime, and since static allocations (and automatic allocations before C99) must 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. (Come across the article on malloc for an example of dynamically allocated arrays.) Dissimilar automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions render an indication (in the form of a zippo arrow value) when the required storage cannot be allocated. (Static allocation that is too big is usually detected by the linker or loader, before the program tin can even begin execution.)

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

Heap memory allocation has to be synchronized with its actual usage in any plan to be reused as much as possible. For example, if the simply pointer to a heap memory allotment goes out of telescopic or has its value overwritten before information technology is deallocated explicitly, then that retentiveness cannot be recovered for afterwards reuse and is essentially lost to the program, a phenomenon known as a retentiveness leak. Conversely, information technology 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 code that causes the error, making it difficult to diagnose the failure. Such issues are ameliorated in languages with automatic garbage collection.

Libraries [edit]

The C programming linguistic communication uses libraries as its master method of extension. In C, a library is a gear up of functions independent within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a plan, and declarations of special information types and macro symbols used with these functions. In order for a program to use a library, it must include the library's header file, and the library must exist linked with the plan, which in many cases requires compiler flags (e.g., -lm, shorthand for "link the math library").^[31]

The nigh common C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation (implementations which target limited environments such equally embedded systems may provide only a subset of the standard library). This library supports stream input and output, retention allotment, mathematics, graphic symbol strings, and time values. Several split standard headers (for example, stdio.h) specify the interfaces for these and other standard library facilities.

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

Since many programs take been written in C, in that location are a broad diversity of other libraries available. Libraries are oftentimes 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 handling and streams [edit]

File input and output (I/O) is non part of the C linguistic communication itself but instead is handled by libraries (such as the C standard library) and their associated header files (east.chiliad. stdio.h). File handling is more often than not implemented through loftier-level I/O which works through streams. A stream is from this perspective a information menses that is contained of devices, while a file is a concrete device. The loftier-level I/O is done through the association of a stream to a file. In the C standard library, a buffer (a retentiveness area or queue) is temporarily used to store information before it's sent to the final destination. This reduces the time spent waiting for slower devices, for example a difficult drive or solid state drive. Low-level I/O functions are not part of the standard C library^{[ clarification needed ]} just are generally office of "bare metal" programming (programming that's independent of any operating arrangement such as most embedded programming). With few exceptions, implementations include low-level I/O.

Language tools [edit]

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

Automated source code checking and auditing are benign in any linguistic communication, and for C many such tools exist, such as Lint. A common practise is to use Lint to detect questionable lawmaking when a program is first written. Once a program passes Lint, it is and so compiled using the C compiler. Also, many compilers can optionally warn about syntactically valid constructs that are likely to really be errors. MISRA C is a proprietary ready of guidelines to avoid such questionable code, developed for embedded systems.^[37]

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

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

Uses [edit]

The C Programming Language

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

C can be used for website programming using the Common Gateway Interface (CGI) every bit 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 most-universal availability.^[40]

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

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

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

C has also been widely used to implement cease-user applications. However, such applications tin also exist written in newer, higher-level languages.

[edit]

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

C has both directly and indirectly influenced many later languages such equally C#, D, Get, Coffee, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix's C vanquish.^[42] The most pervasive influence has been syntactical; all of the languages mentioned combine the statement and (more or less recognizably) expression syntax of C with type systems, data models, and/or large-scale programme structures that differ from those of C, sometimes radically.

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

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

The C++ programming language (originally named "C with Classes") was devised by Bjarne Stroustrup as an approach to providing object-oriented functionality with a C-like syntax.^[44] C++ adds greater typing strength, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Nearly a superset of C, C++ now supports nigh of C, with a few exceptions.

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

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

Meet likewise [edit]

Compatibility of C and C++
Comparison of Pascal and C
Comparison of programming languages
International Obfuscated C Code Competition
List of C-based programming languages
Listing of C compilers

Notes [edit]

^ The original case lawmaking volition compile on virtually modernistic compilers that are not in strict standard compliance mode, but it does not fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic bulletin be produced.
^ The main part actually has two arguments, int argc and char *argv[], respectively, which tin be used to handle command line arguments. The ISO C standard (section 5.one.2.2.1) requires both forms of primary to be supported, which is special handling not afforded to whatever other function.

References [edit]

^ ^a ^b Kernighan, Brian West.; Ritchie, Dennis Thou. (February 1978). The C Programming Language (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, but gave up the effort."
^ Fruderica (December 13, 2020). "History of C". The cppreference.com. Archived from the original on October 24, 2020. Retrieved October 24, 2020.
^ Ritchie (1993): "The scheme of type composition adopted past C owes considerable debt to Algol 68, although information technology did not, peradventure, sally in a form that Algol's adherents would approve of."
^ Ring Squad (October 23, 2021). "The Ring programming language and other languages". band-lang.net.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Enquiry School of Reckoner Science at the Australian National University. June 3, 2010. Archived from the original (PDF) on Nov vi, 2013. Retrieved August 19, 2013. 1980s: ; Verilog start introduced ; Verilog inspired by the C programming language
^ ^a ^b ^c ^d ^e Ritchie (1993)
^ "Programming Language Popularity". 2009. Archived from the original on January 16, 2009. Retrieved January 16, 2009.
^ "TIOBE Programming Community Alphabetize". 2009. Archived from the original on May iv, 2009. Retrieved May vi, 2009.
^ ^a ^b "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
^ "TIOBE Index for October 2021". Retrieved October 7, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on December 12, 2019. Retrieved September x, 2019.
^ ^a ^b Johnson, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX Organization". Bell System Tech. J. 57 (6): 2021–2048. CiteSeerX10.1.1.138.35. 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, One thousand. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical written report). CSTR. Bell Labs. p. 10. 139. Archived (PDF) from the original on November eleven, 2017. Retrieved February 1, 2015.
^ "C manual 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 Car
^ Kernighan, Brian W.; Ritchie, Dennis M. (March 1988). The C Programming Language (2nd ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110362-7.
^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Report). AT&T Labs. Archived (PDF) from the original on August 24, 2014. Retrieved Apr fourteen, 2014.
^ C Integrity. International Organisation for Standardization. March 30, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
^ "JTC1/SC22/WG14 – C". Home page. ISO/IEC. Archived from the original on February 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 Northward 2759" (PDF). www.open up-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October ten, 2021.
^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on February 25, 2021. Retrieved July 26, 2011.
^ Harbison, Samuel P.; Steele, Guy Fifty. (2002). C: A Reference Manual (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-nine. Contains a BNF grammar for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. three.
^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on December 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 October 21, 2008. Retrieved June 26, 2009.
^ Schultz, Thomas (2004). C and the 8051 (tertiary ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-1-58961-237-two. Archived from the original on July 29, 2020. Retrieved Feb x, 2012.
^ Kernighan & Ritchie (1978), p. 6.
^ ^a ^b ^c ^d ^e ^f ^k Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-i-4493-2714-9.
^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparison of the Programming Languages C and Pascal". ACM Computing Surveys. xiv (1): 73–92. doi:10.1145/356869.356872. S2CID 3136859.
^ Kernighan & Ritchie (1996), p. 122.
^ For instance, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Fourth dimension Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January 7, 2007. Retrieved Baronial 5, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-EDUCATION PUBLIC COMPANY Limited. pp. 225–230. ISBN978-616-08-2740-iv.
^ Raymond, Eric Due south. (October 11, 1996). The New Hacker's Lexicon (3rd ed.). MIT Press. p. 432. ISBN978-0-262-68092-ix. Archived from the original on November 12, 2012. Retrieved Baronial 5, 2012.
^ "Human being Page for lint (freebsd Section 1)". unix.com. May 24, 2001. Retrieved July 15, 2014.
^ Dale, Nell B.; Weems, Chip (2014). Programming and problem solving with C++ (6th ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
^ Dr. Dobb'southward Sourcebook. U.Due south.A.: Miller Freeman, Inc. November–December 1995.
^ "Using C for CGI Programming". linuxjournal.com. March 1, 2005. Archived from the original on Feb 13, 2010. Retrieved Jan 4, 2010.
^ McMillan, Robert (August 1, 2013). "Is Java Losing Its Mojo?". Wired. Archived from the original on Feb 15, 2017. Retrieved March 5, 2017.
^ O'Regan, Gerard (September 24, 2015). Pillars of computing : a compendium of select, pivotal engineering firms. ISBN978-3319214641. OCLC 922324121.
^ Rauchwerger, Lawrence (2004). Languages and compilers for parallel computing : 16th international workshop, LCPC 2003, College Station, TX, USA, Oct 2-4, 2003 : revised papers. Springer. ISBN978-3540246442. OCLC 57965544.
^ Stroustrup, Bjarne (1993). "A History of C++: 1979−1991" (PDF). Archived (PDF) from the original on Feb two, 2019. Retrieved June 9, 2011.

Sources [edit]

Ritchie, Dennis M. (March 1993). "The Development of the C Language". ACM SIGPLAN Notices. ACM. 28 (iii): 201–208. doi:10.1145/155360.155580.
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 W.; Ritchie, Dennis M. (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 Frequently Asked Questions
A History of C, past Dennis Ritchie

parsonenterhad1964.blogspot.com

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