C# Read String From Public Partial Class

General-purpose programming language

C
Major implementations
The C Programming Language ^[ane] (often referred to every bit K&R), the seminal volume on C
Image	Multi-paradigm: imperative (procedural), structured
Designed by	Dennis Ritchie
Programmer	Dennis Ritchie & Bell Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
First appeared	1972; 50 years agone (1972) ^[ii]

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

Typing subject	Static, weak, manifest, nominal
Bone	Cross-platform
Filename extensions	.c, .h
Website	www.iso.org/standard/74528.html www.open-std.org/jtc1/sc22/wg14/
pcc, GCC, Clang, Intel C, C++Builder, Microsoft Visual C++, Watcom C
Dialects
Cyclone, Unified Parallel C, Split-C, Cilk, C*
Influenced past
B (BCPL, CPL), ALGOL 68,^[four] assembly, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Go, Coffee, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, State highway, Processing, Python, Band,^[5]Rust, Seed7, Vala, Verilog (HDL),^[6] Nim, Zig
C Programming at Wikibooks

C (, as in the letter c) is a general-purpose, procedural estimator programming language supporting structured programming, lexical variable scope, and recursion, with a static type system. By blueprint, C provides constructs that map efficiently to typical auto instructions. Information technology has found lasting use in applications previously coded in associates linguistic communication. 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 language B, C was originally adult at Bell Labs by Dennis Ritchie betwixt 1972 and 1973 to construct utilities running on Unix. Information technology was applied to re-implementing the kernel of the Unix operating system.^[vii] During the 1980s, C gradually gained popularity. Information technology has become i of the nigh widely used programming languages,^[eight] ^[9] with C compilers from various vendors available for the majority of existing computer architectures and operating systems. C has been standardized past ANSI since 1989 (ANSI C) and by the International Organisation for Standardization (ISO).

C is an imperative procedural language. It was designed to be compiled to provide depression-level access to retention and language constructs that map efficiently to car instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C plan written with portability in heed can be compiled for a wide diversity of figurer platforms and operating systems with few changes to its source code.^[10]

Since 2000, C has consistently ranked amidst the top two languages in the TIOBE alphabetize, a measure of the popularity of programming languages.^[xi]

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 blazon arrangement prevents unintended operations. In C, all executable code is contained within subroutines (as well called "functions", though not strictly in the sense of functional programming). Function parameters are e'er passed by value (except arrays). Pass-by-reference is simulated in C past explicitly passing pointer values. C programme source text is free-format, using the semicolon as a statement terminator and curly braces for group blocks of statements.

The C language also exhibits the following characteristics:

The language has a pocket-sized, fixed number of keywords, including a full set of command flow primitives: if/else, for, practice/while, while, and switch. User-defined names are not distinguished from keywords by whatsoever kind of sigil.
It has a big number of arithmetic, bitwise, and logic operators: +,+=,++,&,||, etc.
More than ane assignment may be performed in a unmarried statement.
Functions:
- Function return values can exist ignored, when not needed.
- Function and information pointers allow ad hoc run-time polymorphism.
- Functions may non exist defined inside the lexical scope of other functions.
Data typing is static, but weakly enforced; all data has a type, but implicit conversions are possible.
Declaration syntax mimics usage context. C has no "ascertain" keyword; instead, a statement beginning with the name of a blazon is taken equally a declaration. 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) permit related data elements to be accessed and assigned every bit a unit of measurement.
- Union is a structure with overlapping members; but the last member stored is valid.
- Array indexing is a secondary notation, defined in terms of pointer arithmetics. Different structs, arrays are not first-class objects: they cannot be assigned or compared using single congenital-in operators. There is no "assortment" keyword in use or definition; instead, square brackets signal arrays syntactically, for example month[eleven].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are not a distinct data type, but are conventionally implemented as naught-terminated character arrays.
Low-level access to calculator memory is possible by converting machine addresses to typed pointers.
Procedures (subroutines not returning values) are a special case of part, with an untyped return type void.
A preprocessor performs macro definition, source lawmaking file inclusion, and conditional compilation.
There is a basic grade of modularity: files can be compiled separately and linked together, with control over which functions and information objects are visible to other files via static and extern attributes.
Complex functionality such equally I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

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

Relations to other languages [edit]

Many later languages have borrowed directly or indirectly from C, including C++, C#, Unix's C beat, D, Go, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[6] These languages accept drawn many of their control structures and other basic features from C. Most of them (Python being a dramatic exception) as well limited highly similar syntax to C, and they tend to combine the recognizable expression and argument syntax of C with underlying blazon systems, data models, and semantics that can exist radically different.

History [edit]

Early developments [edit]

Timeline of language development
Yr	C Standard^[10]
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 organisation, originally implemented in assembly language on a PDP-7 past Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Somewhen, they decided to port the operating system to a PDP-11. The original PDP-11 version of Unix was also developed in assembly linguistic communication.^[7]

Thompson desired a programming language to brand utilities for the new platform. At first, he tried to brand a Fortran compiler, merely presently gave up the idea. Instead, he created a cut-down version of the recently developed BCPL systems programming language. The official description of BCPL was non available at the time,^[12] and Thompson modified the syntax to exist less wordy, producing the similar but somewhat simpler B.^[7] However, few utilities were ultimately written in B because information technology was too tiresome, and B could not accept advantage of PDP-eleven features such as byte addressability.

In 1972, Ritchie started to improve B, almost notably adding data typing for variables, which resulted in creating a new language C.^[thirteen] The C compiler and some utilities made with information technology were included in Version ii Unix.^[14]

At Version 4 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 as well in recognition of the usefulness of the file-inclusion mechanisms bachelor in BCPL and PL/I. Its original version provided only included files and unproblematic string replacements: #include and #define of parameterless macros. Shortly afterwards that, it was extended, mostly by Mike Lesk and so past John Reiser, to comprise macros with arguments and conditional compilation.^[vii]

Unix was one of the first operating organization kernels implemented in a language other than associates. 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 effectually 1977, Ritchie and Stephen C. Johnson made further changes to the linguistic communication to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served as the basis for several implementations of C on new platforms.^[13]

K&R C [edit]

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

Thou&R introduced several language features:

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

Even subsequently 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 still in utilise, and because carefully written M&R C code tin be legal Standard C as well.

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

For example:

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

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

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

In the years following the publication of K&R C, several features were added to the language, supported past 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 non 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 broad variety of mainframe computers, minicomputers, and microcomputers, including the IBM PC, as its popularity began to increment significantly.

In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to found a standard specification of C. X3J11 based the C standard on the Unix implementation; all the same, 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 often 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, similar other national standards bodies, no longer develops the C standard independently, but 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 inside a year of ISO publication.

One of the aims of the C standardization process was to produce a superset of G&R C, incorporating many of the afterwards introduced unofficial features. The standards commission also included several additional features such as office prototypes (borrowed from C++), void pointers, support for international grapheme sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the mode used in C++, the One thousand&R interface continued to be permitted, for compatibility with existing source code.

C89 is supported by current C compilers, and almost modern C lawmaking is based on it. Any program written just in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a befitting C implementation, within its resources limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for case, to the apply of not-standard libraries, such every bit GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness.

In cases where code must be compilable by either standard-conforming or Chiliad&R C-based compilers, the __STDC__ macro tin can be used to split the code into Standard and Thou&R sections to forbid the utilise on a Yard&R C-based compiler of features bachelor only in Standard C.

Later the ANSI/ISO standardization procedure, the C language specification remained relatively static for several years. In 1995, Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive back up for international character sets.^[eighteen]

C99 [edit]

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

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

C99 is for the virtually role backward compatible with C90, only 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 divers with value 199901L to betoken that C99 support is bachelor. GCC, Solaris Studio, and other C compilers at present 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.^[20] ^{[ needs update ]}

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

C11 [edit]

In 2007, piece of work began on another revision of the C standard, informally called "C1X" until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested past existing implementations.

The C11 standard adds numerous new features to C and the library, including blazon generic macros, bearding structures, improved Unicode back up, atomic operations, multi-threading, and bounds-checked functions. It as well makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__ is defined as 201112L to bespeak that C11 back up is available.

C17 [edit]

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

C2x [edit]

C2x is an informal proper noun for the adjacent (after C17) major C linguistic communication standard revision. It is expected to exist 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 linguistic communication in order to back up exotic features such as stock-still-betoken arithmetic, multiple distinct memory banks, and basic I/O operations.

In 2008, the C Standards Commission published a technical report extending the C linguistic communication^[22] to address these issues past providing a common standard for all implementations to adhere to. Information technology includes a number of features non available in normal C, such as fixed-bespeak 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 non significant in C; however, line boundaries do accept significance during the preprocessing phase. Comments may appear either between the delimiters /* and */, or (since C99) post-obit // until the cease of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as annotate delimiters if they appear inside cord or character literals.^[24]

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

As an imperative language, C uses statements to specify actions. The well-nigh common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side effect of the evaluation, functions may be called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several 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 separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. intermission and continue can exist used to leave the innermost enclosing loop statement or skip to its reinitialization. In that location is also a non-structured goto statement which branches directly to the designated characterization within the function. switch selects a example to be executed based on the value of an integer expression.

Expressions tin utilize a variety of congenital-in operators and may incorporate function calls. The order in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next "sequence point"; sequence points include the end of each expression argument, and the entry to and return from each office call. Sequence points besides occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a high degree of object code optimization by the compiler, just requires C programmers to take more than care to obtain reliable results than is needed for other programming languages.

Kernighan and Ritchie say in the Introduction of The C Programming Linguistic communication: "C, similar any other language, has its blemishes. Some of the operators accept the wrong precedence; some parts of the syntax could be better."^[25] The C standard did non endeavour to correct many of these blemishes, because of the impact of such changes on already existing software.

Graphic symbol set [edit]

The basic C source character set includes the following characters:

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

Newline indicates the terminate of a text line; it need non represent to an actual unmarried graphic symbol, although for convenience C treats it as one.

Additional multi-byte encoded characters may be used in string literals, but they are non entirely portable. The latest C standard (C11) allows multi-national Unicode characters to be embedded portably inside C source text by using \uXXXX or \UXXXXXXXX encoding (where the X denotes a hexadecimal character), although this feature is non yet widely implemented.

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

Reserved words [edit]

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

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

C99 reserved 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 begin with an underscore followed by a upper-case letter, considering identifiers of that form were previously reserved past the C standard for utilise but by implementations. Since existing program source lawmaking should non have been using these identifiers, it would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers do define more user-friendly synonyms for underscored identifiers. The language previously included a reserved give-and-take called entry, simply this was seldom implemented, and has at present been removed as a reserved word.^[27]

Operators [edit]

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

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

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

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

"Hi, world" example [edit]

The "hello, world" case, which appeared in the first edition of G&R, has become the model for an introductory program in nigh programming textbooks. The program prints "hello, world" to the standard output, which is usually a terminal or screen display.

The original version was:^[thirty]

                        main            ()                        {                                                printf            (            "hullo, world            \northward            "            );                        }

A standard-conforming "how-do-you-do, world" programme is:^[a]

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

The outset line of the program contains a preprocessing directive, indicated by #include. This causes the compiler to replace that line with the entire text of the stdio.h standard header, which contains declarations for standard input and output functions such as printf and scanf. The angle brackets surrounding stdio.h indicate that stdio.h is located using a search strategy that prefers headers provided with the compiler to other headers having the same proper noun, as opposed to double quotes which typically include local or project-specific header files.

The next line indicates that a part named main is beingness defined. The principal function serves a special purpose in C programs; the run-fourth dimension surroundings calls the principal function to begin plan 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 primary part, is an integer. The keyword void as a parameter list indicates that this part takes no arguments.^[b]

The opening curly brace indicates the beginning of the definition of the master function.

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

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

Data types [edit]

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

C is often used in low-level systems programming where escapes from the type system may exist necessary. The compiler attempts to ensure type definiteness of about expressions, only the programmer tin can override the checks in diverse ways, either by using a blazon cast to explicitly convert a value from one type to another, or by using pointers or unions to reinterpret the underlying $.25 of a data object in another manner.

Some detect C's annunciation syntax unintuitive, particularly for role pointers. (Ritchie'south thought was to declare identifiers in contexts resembling their use: "proclamation reflects use".)^[33]

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

A nix pointer value explicitly points to no valid location. Dereferencing a naught arrow value is undefined, often resulting in a segmentation fault. Nada pointer values are useful for indicating special cases such as no "next" arrow in the final node of a linked listing, or every bit an error indication from functions returning pointers. In appropriate contexts in source lawmaking, such equally for assigning to a pointer variable, a null pointer abiding tin be written as 0, with or without explicit casting to a pointer type, or as the NULL macro defined past several standard headers. In conditional contexts, null pointer values evaluate to imitation, while all other pointer values evaluate to true.

Void pointers (void *) point to objects of unspecified type, and tin therefore exist used as "generic" data pointers. Since the size and blazon 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]

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

Arrays [edit]

Assortment types in C are traditionally of a stock-still, static size specified at compile time. The more recent C99 standard also allows a form of variable-length arrays. However, it is also possible to allocate a block of memory (of capricious size) at run-fourth dimension, using the standard library'southward malloc function, and treat it equally an array.

Since arrays are ever accessed (in consequence) via pointers, array accesses are typically non checked against the underlying assortment size, although some compilers may provide premises checking every bit an option.^[34] ^[35] Assortment premises violations are therefore possible and can atomic number 82 to various repercussions, including illegal memory accesses, corruption of data, buffer overruns, and run-fourth dimension exceptions.

C does not take 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 aforementioned thing. The index values of the resulting "multi-dimensional array" can exist thought of equally increasing in row-major order. Multi-dimensional arrays are usually used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C assortment is well suited to this item job. However, 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 classify the array with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this issue.

The following example using modern C (C99 or afterward) shows allocation of a 2-dimensional array on the heap and the employ of multi-dimensional assortment indexing for accesses (which tin employ bounds-checking on many C compilers):

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

Array–arrow interchangeability [edit]

The subscript notation ten[i] (where x designates a pointer) is syntactic carbohydrate for *(10+i).^[36] Taking advantage of the compiler's cognition of the pointer type, the address that ten + i points to is not the base address (pointed to by x) 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, x[i] designates the i+ith element of the array.

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

The total size of an array x tin be determined by applying sizeof to an expression of array type. The size of an element tin be adamant by applying the operator sizeof to any dereferenced chemical element of an array A, every bit in n = sizeof A[0]. This, the number of elements in a declared assortment A can exist adamant as sizeof A / sizeof A[0]. Note, that if only a pointer to the beginning element is available equally it is often the case in C lawmaking because of the automatic conversion described in a higher place, the information about the full type of the assortment and its length are lost.

Retentivity direction [edit]

One of the most important functions of a programming language is to provide facilities for managing memory and the objects that are stored in retentiveness. C provides three distinct means to allocate memory for objects:^[31]

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

These three approaches are appropriate in different situations and have various merchandise-offs. For example, static retentiveness allotment has little allotment overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially accept a smashing 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 like shooting fish in a barrel to utilise but stack infinite is typically much more limited and transient than either static retention or heap infinite, and dynamic retentiveness allocation allows user-friendly allocation of objects whose size is known only at run-time. Most C programs make extensive utilise of all three.

Where possible, automated or static allocation is usually simplest because the storage is managed by the compiler, freeing the programmer of the potentially error-prone task of manually allocating and releasing storage. All the same, many data structures can modify 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. (See the article on malloc for an instance of dynamically allocated arrays.) Unlike automatic allocation, which tin fail at run fourth dimension with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a goose egg 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 fifty-fifty brainstorm execution.)

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

Heap memory allocation has to be synchronized with its actual usage in any program to exist reused as much as possible. For instance, if the but arrow to a heap memory allocation goes out of scope or has its value overwritten before it is deallocated explicitly, and then that retentivity cannot be recovered for after reuse and is essentially lost to the program, a phenomenon known as a retention leak. Conversely, information technology is possible for memory to exist freed, but is referenced later on, leading to unpredictable results. Typically, the failure symptoms appear in a portion of the program unrelated to the code that causes the error, making it hard to diagnose the failure. Such issues are ameliorated in languages with automated garbage drove.

Libraries [edit]

The C programming language uses libraries equally its chief method of extension. In C, a library is a set of functions contained inside a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained inside the library that may be used past a program, and declarations of special data types and macro symbols used with these functions. In lodge for a programme to employ a library, it must include the library's header file, and the library must exist linked with the program, which in many cases requires compiler flags (eastward.m., -lm, shorthand for "link the math library").^[31]

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

Another common ready of C library functions are those used past 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 equally POSIX and the Single UNIX Specification.

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

File handling and streams [edit]

File input and output (I/O) is not part of the C language itself merely instead is handled by libraries (such as the C standard library) and their associated header files (e.1000. stdio.h). File handling is mostly implemented through high-level I/O which works through streams. A stream is from this perspective a data catamenia 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 memory expanse or queue) is temporarily used to shop data 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 bulldoze. Depression-level I/O functions are not office of the standard C library^{[ clarification needed ]} but are mostly part of "bare metallic" programming (programming that'due south independent of whatsoever operating system such as near embedded programming). With few exceptions, implementations include low-level I/O.

Linguistic communication tools [edit]

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

Automated source code checking and auditing are beneficial in any linguistic communication, and for C many such tools be, such as Lint. A common practice is to use Lint to detect questionable lawmaking when a program is first written. Once a programme passes Lint, it is then compiled using the C compiler. As well, many compilers can optionally warn about syntactically valid constructs that are probable to really be errors. MISRA C is a proprietary set of guidelines to avert such questionable code, adult for embedded systems.^[37]

There are also compilers, libraries, and operating organization level mechanisms for performing actions that are not a standard part of C, such equally bounds checking for arrays, detection of buffer overflow, serialization, dynamic retentivity tracking, and automatic garbage collection.

Tools such equally Purify or Valgrind and linking with libraries containing special versions of the memory allocation functions can assistance 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 system applications,^[38] considering C code, when written for portability, can be used for about purposes, nevertheless 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-time demand on system resources.

C tin can be used for website programming using the Mutual Gateway Interface (CGI) as a "gateway" for data between the Spider web awarding, the server, and the browser.^[39] C is oftentimes chosen over interpreted languages considering of its speed, stability, and near-universal availability.^[forty]

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 case, 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 brainchild from hardware is thin, and its overhead is low, an important criterion for computationally intensive programs. For instance, the GNU Multiple Precision Arithmetics Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.

C is sometimes used as an intermediate language past implementations of other languages. This arroyo may be used for portability or convenience; by using C as an intermediate language, additional auto-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 besides been widely used to implement cease-user applications. However, such applications can likewise be written in newer, higher-level languages.

[edit]

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

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

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

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

The C++ programming linguistic communication (originally named "C with Classes") was devised by Bjarne Stroustrup every bit 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. Near a superset of C, C++ at present supports about of C, with a few exceptions.

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

Meet also [edit]

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

Notes [edit]

^ The original case code volition compile on nearly mod compilers that are non 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 message be produced.
^ The main role really has two arguments, int argc and char *argv[], respectively, which tin be used to handle control line arguments. The ISO C standard (section 5.1.two.two.one) requires both forms of main to be supported, which is special handling not afforded to any other office.

References [edit]

^ ^a ^b Kernighan, Brian W.; Ritchie, Dennis M. (February 1978). The C Programming Language (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110163-0.
^ Ritchie (1993): "Thompson had fabricated a brief attempt to produce a system coded in an early version of C—before structures—in 1972, just gave upwardly the endeavour."
^ Fruderica (December xiii, 2020). "History of C". The cppreference.com. Archived from the original on Oct 24, 2020. Retrieved October 24, 2020.
^ Ritchie (1993): "The scheme of type composition adopted by C owes considerable debt to Algol 68, although it did not, perhaps, emerge in a form that Algol's adherents would approve of."
^ Ring Squad (October 23, 2021). "The Ring programming language and other languages". band-lang.internet.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Research School of Reckoner Scientific discipline at the Australian National University. June iii, 2010. Archived from the original (PDF) on November 6, 2013. Retrieved Baronial 19, 2013. 1980s: ; Verilog first introduced ; Verilog inspired past the C programming language
^ ^a ^b ^c ^d ^e Ritchie (1993)
^ "Programming Linguistic communication Popularity". 2009. Archived from the original on January sixteen, 2009. Retrieved Jan 16, 2009.
^ "TIOBE Programming Community Index". 2009. Archived from the original on May 4, 2009. Retrieved May 6, 2009.
^ ^a ^b "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
^ "TIOBE Alphabetize for October 2021". Retrieved Oct 7, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on Dec 12, 2019. Retrieved September 10, 2019.
^ ^a ^b Johnson, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX System". Bell Organization Tech. J. 57 (six): 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" equally "IBM 310".)
^ McIlroy, M. D. (1987). A Enquiry Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bong Labs. p. 10. 139. Archived (PDF) from the original on November xi, 2017. Retrieved February 1, 2015.
^ "C transmission pages". FreeBSD Miscellaneous Information Manual (FreeBSD 13.0 ed.). May 30, 2011. Archived from the original on January 21, 2021. Retrieved January 15, 2021. [1] Archived Jan 21, 2021, at the Wayback Machine
^ Kernighan, Brian W.; Ritchie, Dennis M. (March 1988). The C Programming Language (second ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110362-7.
^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Study). AT&T Labs. Archived (PDF) from the original on August 24, 2014. Retrieved April 14, 2014.
^ C Integrity. International System for Standardization. March xxx, 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 two, 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 fourteen N 2759" (PDF). world wide web.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October 10, 2021.
^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on February 25, 2021. Retrieved July 26, 2011.
^ Harbison, Samuel P.; Steele, Guy L. (2002). C: A Reference Manual (fifth ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-nine. Contains a BNF grammar for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. 3.
^ "ISO/IEC 9899:201x (ISO C11) Commission 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 (tertiary ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-1-58961-237-ii. Archived from the original on July 29, 2020. Retrieved February 10, 2012.
^ Kernighan & Ritchie (1978), p. 6.
^ ^a ^b ^c ^d ^e ^f ^g Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-1-4493-2714-9.
^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparison of the Programming Languages C and Pascal". ACM Calculating Surveys. 14 (one): 73–92. doi:x.1145/356869.356872. S2CID 3136859.
^ Kernighan & Ritchie (1996), p. 122.
^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on Jan vii, 2007. Retrieved August five, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-EDUCATION PUBLIC Visitor Express. pp. 225–230. ISBN978-616-08-2740-4.
^ Raymond, Eric S. (October 11, 1996). The New Hacker's Lexicon (3rd ed.). MIT Press. p. 432. ISBN978-0-262-68092-nine. Archived from the original on November 12, 2012. Retrieved Baronial 5, 2012.
^ "Man Page for lint (freebsd Section i)". unix.com. May 24, 2001. Retrieved July 15, 2014.
^ Dale, Nell B.; Weems, Chip (2014). Programming and problem solving with C++ (sixth ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
^ Dr. Dobb's Sourcebook. U.S.A.: Miller Freeman, Inc. November–Dec 1995.
^ "Using C for CGI Programming". linuxjournal.com. March 1, 2005. Archived from the original on Feb thirteen, 2010. Retrieved January four, 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 technology firms. ISBN978-3319214641. OCLC 922324121.
^ Rauchwerger, Lawrence (2004). Languages and compilers for parallel computing : 16th international workshop, LCPC 2003, College Station, TX, USA, October 2-4, 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 ii, 2019. Retrieved June 9, 2011.

Sources [edit]

Ritchie, Dennis Thousand. (March 1993). "The Development of the C Linguistic communication". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:10.1145/155360.155580.
Ritchie, Dennis Yard. (1993). "The Development of the C Language". The 2d 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 iv, 2014.
Kernighan, Brian Westward.; Ritchie, Dennis Chiliad. (1996). The C Programming Language (2d 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). (three.61 MB)
comp.lang.c Often Asked Questions
A History of C, by Dennis Ritchie

villanuevaingents.blogspot.com

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