C# Edi Read a File Into a Class

General-purpose programming language

C
Major implementations
The C Programming Language ^[1] (often referred to equally K&R), the seminal book on C
Paradigm	Multi-epitome: imperative (procedural), structured
Designed by	Dennis Ritchie
Developer	Dennis Ritchie & Bell Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
First appeared	1972; 50 years ago (1972) ^[ii]

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

Typing discipline	Static, weak, manifest, nominal
OS	Cantankerous-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
Whirlwind, Unified Parallel C, Separate-C, Cilk, C*
Influenced past
B (BCPL, CPL), ALGOL 68,^[iv] associates, PL/I, FORTRAN
Influenced
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Get, Java, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Superhighway, Processing, Python, Band,^[five]Rust, Seed7, Vala, Verilog (HDL),^[six] Nim, Zig
C Programming at Wikibooks

C (, as in the letter c) is a general-purpose, procedural reckoner programming linguistic communication supporting structured programming, lexical variable telescopic, and recursion, with a static type system. By design, C provides constructs that map efficiently to typical machine instructions. It has establish lasting apply in applications previously coded in assembly language. Such applications include operating systems and diverse application software for computer architectures that range from supercomputers to PLCs and embedded systems.

A successor to the programming language B, C was originally developed at Bell Labs by Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. Information technology was applied to re-implementing the kernel of the Unix operating system.^[7] During the 1980s, C gradually gained popularity. It has get 1 of the near widely used programming languages,^[eight] ^[nine] with C compilers from various vendors available for the majority of existing figurer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and by the International Organization for Standardization (ISO).

C is an imperative procedural language. Information technology was designed to be compiled to provide depression-level access to memory and linguistic communication constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its depression-level capabilities, the linguistic communication was designed to encourage cross-platform programming. A standards-compliant C program written with portability in heed can be compiled for a wide variety of computer platforms and operating systems with few changes to its source code.^[x]

Since 2000, C has consistently ranked among the top 2 languages in the TIOBE index, a measure of the popularity of programming languages.^[xi]

Overview [edit]

Like almost procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type arrangement prevents unintended operations. In C, all executable code is contained inside subroutines (also called "functions", though not strictly in the sense of functional programming). Function 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 costless-format, using the semicolon as a argument terminator and curly braces for group blocks of statements.

The C language besides exhibits the following characteristics:

The language has a pocket-sized, fixed number of keywords, including a full set of control flow primitives: if/else, for, do/while, while, and switch. User-defined names are non distinguished from keywords by any kind of sigil.
Information technology has a large number of arithmetics, bitwise, and logic operators: +,+=,++,&,||, etc.
More than one assignment may be performed in a single argument.
Functions:
- Function return values can be ignored, when not needed.
- Office and data pointers permit advertizement hoc run-time polymorphism.
- Functions may not exist defined within the lexical scope of other functions.
Information typing is static, merely weakly enforced; all data has a type, but implicit conversions are possible.
Annunciation syntax mimics usage context. C has no "define" keyword; instead, a statement beginning with the name of a type is taken equally a declaration. There is no "role" keyword; instead, a function is indicated by the presence of a parenthesized argument listing.
User-defined (typedef) and compound types are possible.
- Heterogeneous aggregate data types (struct) let related information elements to be accessed and assigned as a unit.
- Union is a construction with overlapping members; only the last member stored is valid.
- Assortment indexing is a secondary note, divers in terms of pointer arithmetics. Dissimilar structs, arrays are not first-class objects: they cannot be assigned or compared using single built-in operators. There is no "assortment" keyword in use or definition; instead, square brackets betoken arrays syntactically, for case calendar month[11].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are non a distinct information type, just are conventionally implemented as null-terminated grapheme arrays.
Low-level access to computer memory is possible by converting machine addresses to typed pointers.
Procedures (subroutines non returning values) are a special case of function, with an untyped return type void.
A preprocessor performs macro definition, source lawmaking file inclusion, and conditional compilation.
There is a bones form of modularity: files tin exist 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 every bit 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 equally object orientation and garbage collection), these can be implemented or emulated, often through the employ of external libraries (e.yard., 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's C shell, D, Go, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Red, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^[6] These languages have drawn many of their control structures and other basic features from C. Nigh of them (Python existence a dramatic exception) also limited highly similar syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, information models, and semantics that can exist radically different.

History [edit]

Early developments [edit]

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

Thompson desired a programming language to make utilities for the new platform. At first, he tried to make a Fortran compiler, simply soon gave upwardly the idea. Instead, he created a cutting-down version of the recently adult BCPL systems programming language. The official description of BCPL was not available at the time,^[12] and Thompson modified the syntax to be less wordy, producing the similar but somewhat simpler B.^[seven] Withal, few utilities were ultimately written in B considering it was too slow, and B could not accept advantage of PDP-11 features such as byte addressability.

In 1972, Ritchie started to meliorate B, most notably calculation information typing for variables, which resulted in creating a new linguistic communication C.^[13] The C compiler and some utilities fabricated with it were included in Version 2 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 language had caused some powerful features such equally struct types.

The preprocessor was introduced effectually 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 uncomplicated string replacements: #include and #ascertain of parameterless macros. Soon after that, it was extended, mostly by Mike Lesk then past John Reiser, to incorporate macros with arguments and provisional compilation.^[7]

Unix was 1 of the first operating system kernels implemented in a linguistic communication other than assembly. Before instances include the Multics system (which was written in PL/I) and Primary Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson'southward Portable C Compiler served as the footing for several implementations of C on new platforms.^[13]

Grand&R C [edit]

In 1978, Brian Kernighan and Dennis Ritchie published the kickoff edition of The C Programming Language.^[1] This book, known to C programmers as Thou&R, served for many years as an informal specification of the language. The version of C that information technology describes is commonly referred to every bit "K&R C". Equally this was released in 1978, it is also referred to as C78.^[15] The second edition of the book^[xvi] covers the afterwards ANSI C standard, described below.

1000&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 equally =-) were changed to the class op= (that is, -=) to remove the semantic ambiguity created by constructs such as i=-x, which had been interpreted as i =- 10 (decrement i by x) instead of the possibly intended i = -10 (let i exist −ten).

Even later the publication of the 1989 ANSI standard, for many years K&R C was nonetheless considered the "everyman common denominator" to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C lawmaking tin can exist legal Standard C as well.

In early versions of C, only functions that return types other than int must exist alleged if used before the function definition; functions used without prior announcement were presumed to render type int.

For case:

                        long                                    some_function            ();                        /* int */                                    other_function            ();                        /* int */                                    calling_function            ()                        {                                                long                                    test1            ;                                                register                                    /* int */                                    test2            ;                                                test1                                    =                                    some_function            ();                                                if                                    (            test1                                    >                                    1            )                                                test2                                    =                                    0            ;                                                else                                                test2                                    =                                    other_function            ();                                                return                                    test2            ;                        }

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

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

In the years following the publication of K&R C, several features were added to the language, supported by compilers from AT&T (in particular PCC^[17]) and some other vendors. These included:

void functions (i.e., functions with no return value)
functions returning struct or union types (rather than pointers)
assignment for struct information types
enumerated types

The big number of extensions and lack of understanding on a standard library, together with the language popularity and the fact that non even 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 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 commission, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to the IEEE working group 1003 to go the ground for the 1988 POSIX standard. In 1989, the C standard was ratified every bit ANSI X3.159-1989 "Programming Linguistic communication C". This version of the language is ofttimes referred to as ANSI C, Standard C, or sometimes C89.

In 1990, the ANSI C standard (with formatting changes) was adopted past the International Organization for Standardization (ISO) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the aforementioned 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 grouping ISO/IEC JTC1/SC22/WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication.

Ane of the aims of the C standardization process was to produce a superset of K&R C, incorporating many of the subsequently introduced unofficial features. The standards committee also included several boosted features such every bit function prototypes (borrowed from C++), void pointers, back up 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 K&R interface connected to exist permitted, for compatibility with existing source code.

C89 is supported by current C compilers, and most modern C code is based on it. Any programme written only in Standard C and without whatever hardware-dependent assumptions volition run correctly on any platform with a conforming C implementation, inside its resource limits. Without such precautions, programs may compile only on a sure platform or with a particular compiler, due, for case, to the utilise of not-standard libraries, such every bit GUI libraries, or to a reliance on compiler- or platform-specific attributes such equally the exact size of data types and byte endianness.

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

Afterward the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Subpoena 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to right some details and to add more extensive support for international graphic symbol sets.^[18]

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 usually referred to as "C99". It 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 circuitous type to represent complex numbers), variable-length arrays and flexible array members, improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity), and back up for ane-line comments beginning with //, equally in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.

C99 is for the about role backward uniform with C90, but is stricter in some ways; in detail, a annunciation that lacks a type specifier no longer has int implicitly causeless. A standard macro __STDC_VERSION__ is defined with value 199901L to bespeak 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++eleven.^[20] ^{[ needs update ]}

In add-on, back up for Unicode identifiers (variable / function names) in the course of escaped characters (e.g. \U0001f431) is at present 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, bearding structures, improved Unicode support, diminutive 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 linguistic communication. 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 side by side (after C17) major C language standard revision. It is expected to be voted on in 2023 and would therefore be chosen C23.^[21] ^{[ improve source needed ]}

Embedded C [edit]

Historically, embedded C programming requires nonstandard extensions to the C language in lodge to back up exotic features such as stock-still-signal arithmetic, multiple singled-out retentivity banks, and basic I/O operations.

In 2008, the C Standards Commission published a technical written report extending the C linguistic communication^[22] to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not bachelor in normal C, such as fixed-indicate arithmetics, 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; notwithstanding, line boundaries do have 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 */ do not nest, and these sequences of characters are non interpreted as comment delimiters if they appear inside string or character literals.^[24]

C source files contain declarations and role definitions. Function definitions, in turn, contain declarations and statements. Declarations either ascertain new types using keywords such as struct, union, and enum, or assign types to and perchance reserve storage for new variables, usually by writing the blazon followed by the variable proper noun. Keywords such as char and int specify congenital-in types. Sections of lawmaking are enclosed in braces ({ and }, sometimes chosen "curly brackets") to limit the scope of declarations and to human action equally a single argument for command structures.

As an imperative linguistic communication, C uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to exist evaluated, followed past a semicolon; as a side effect of the evaluation, functions may be called and variables may be assigned new values. To change the normal sequential execution of statements, C provides several control-menstruum statements identified past reserved keywords. Structured programming is supported by if … [else] provisional execution and by do … while, while, and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, whatever or all of which tin can be omitted. break and proceed can exist used to exit the innermost enclosing loop statement or skip to its reinitialization. There is as well a not-structured goto statement which branches direct to the designated label within the function. switch selects a case to be executed based on the value of an integer expression.

Expressions can employ a variety of congenital-in operators and may contain function calls. The order in which arguments to functions and operands to virtually operators are evaluated is unspecified. The evaluations may even exist interleaved. All the same, all side furnishings (including storage to variables) will occur earlier the side by side "sequence point"; sequence points include the end of each expression statement, and the entry to and return from each role call. Sequence points as well occur during evaluation of expressions containing sure operators (&&, ||, ?: and the comma operator). This permits a high degree of object code optimization by the compiler, but requires C programmers to accept more care to obtain reliable results than is needed for other programming languages.

Kernighan and Ritchie say in the Introduction of The C Programming Linguistic communication: "C, similar whatsoever other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be meliorate."^[25] The C standard did not endeavour to correct many of these blemishes, because of the touch on of such changes on already existing software.

Character fix [edit]

The bones C source character gear up includes the following characters:

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

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

Additional 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 Ten denotes a hexadecimal graphic symbol), although this characteristic is not notwithstanding widely implemented.

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

Reserved words [edit]

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

machine
break
example
char
const
proceed
default
practice
double
else
enum
extern
bladder
for
goto
if
int
long
register
render
brusque
signed
sizeof
static
struct
switch
typedef
union
unsigned
void
volatile
while

C99 reserved five more words:

_Bool
_Complex
_Imaginary
inline
restrict

C11 reserved 7 more words:^[26]

_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert
_Thread_local

Nigh of the recently reserved words begin with an underscore followed past a upper-case letter letter of the alphabet, considering identifiers of that form were previously reserved past the C standard for use only by implementations. Since existing program source lawmaking should not accept been using these identifiers, information technology would not exist afflicted when C implementations started supporting these extensions to the programming linguistic communication. Some standard headers do define more convenient synonyms for underscored identifiers. The language previously included a reserved word called entry, but this was seldom implemented, and has now been removed as a reserved word.^[27]

Operators [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:

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

C uses the operator = (used in mathematics to express equality) to indicate assignment, following the precedent of Fortran and PL/I, but unlike ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these ii operators (assignment and equality) may outcome in the accidental utilise of one in identify of the other, and in many cases, the mistake does not produce an error message (although some compilers produce warnings). For example, the conditional expression if (a == b + 1) might mistakenly exist written as if (a = b + i), which volition be evaluated as truthful if a is not zip after the assignment.^[28]

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

"Hello, world" example [edit]

The "hello, world" example, which appeared in the beginning edition of One thousand&R, has become the model for an introductory program in most programming textbooks. The program prints "hello, earth" to the standard output, which is normally a terminal or screen display.

The original version was:^[30]

                        main            ()                        {                                                printf            (            "howdy, world            \north            "            );                        }

A standard-befitting "hello, globe" program is:^[a]

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

The commencement line of the plan 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 aforementioned name, as opposed to double quotes which typically include local or project-specific header files.

The adjacent line indicates that a function named main is being divers. The main function serves a special purpose in C programs; the run-time environs calls the master function to begin plan execution. The blazon specifier int indicates that the value that is returned to the invoker (in this example the run-fourth dimension environment) as a result of evaluating the main part, is an integer. The keyword void every bit a parameter listing indicates that this role takes no arguments.^[b]

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

The next line calls (diverts execution to) a function named printf, which in this case is supplied from a organisation library. In this call, the printf function is passed (provided with) a unmarried argument, the accost of the first grapheme in the cord literal "hello, earth\northward". The string literal is an unnamed assortment with elements of type char, fix up automatically past the compiler with a terminal 0-valued character to marking the end of the array (printf needs to know this). The \n is an escape sequence that C translates to a newline grapheme, which on output signifies the cease of the electric current line. The return value of the printf function is of type int, merely information technology is silently discarded since it is not used. (A more than conscientious program might test the return value to determine whether or non the printf role succeeded.) The semicolon ; terminates the statement.

The closing curly brace indicates the finish of the lawmaking for the main function. Co-ordinate to the C99 specification and newer, the main role, unlike whatever other office, volition implicitly render a value of 0 upon reaching the } that terminates the role. (Formerly an explicit render 0; statement was required.) This is interpreted by the run-fourth dimension organisation as an leave code indicating successful execution.^[31]

Data types [edit]

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

C is often used in low-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure type correctness of most expressions, but the programmer tin can override the checks in various ways, either by using a blazon bandage to explicitly convert a value from i type to another, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way.

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

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

Pointers [edit]

C supports the use of pointers, a blazon of reference that records the accost or location of an object or part in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using consignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (peradventure augmented by an offset-within-give-and-take field), but since a arrow'south type includes the blazon of the thing pointed to, expressions including pointers can be blazon-checked at compile time. Arrow arithmetic is automatically scaled by the size of the pointed-to data type. Pointers are used for many purposes in C. Text strings are commonly manipulated using pointers into arrays of characters. Dynamic retentiveness allocation is performed using pointers. Many data types, such equally copse, are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to college-order functions (such as qsort or bsearch) or as callbacks to be invoked by event handlers.^[31]

A null pointer value explicitly points to no valid location. Dereferencing a cypher pointer value is undefined, often resulting in a sectionalization fault. Goose egg pointer values are useful for indicating special cases such equally no "side by side" pointer in the last node of a linked list, or as an error indication from functions returning pointers. In appropriate contexts in source code, such equally for assigning to a pointer variable, a nada pointer abiding can be written as 0, with or without explicit casting to a pointer blazon, or as the NULL macro defined by several standard headers. In conditional contexts, null pointer values evaluate to false, while all other pointer values evaluate to true.

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

Devil-may-care use of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable can be fabricated to signal to any arbitrary location, which tin cause undesirable furnishings. Although properly used pointers point to safe places, they can be made to bespeak to unsafe places by using invalid pointer arithmetics; the objects they betoken to may go along to be used after deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may be directly assigned an unsafe value using a cast, wedlock, or through some other corrupt pointer. In full general, C is permissive in allowing manipulation of and conversion betwixt pointer types, although compilers typically provide options for diverse levels of checking. Some other programming languages address these problems past using more restrictive reference types.

Arrays [edit]

Array types in C are traditionally of a stock-still, static size specified at compile time. The more than recent C99 standard also allows a class of variable-length arrays. However, information technology is likewise possible to allocate a block of memory (of arbitrary size) at run-time, using the standard library's malloc function, and treat information technology as an array.

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

C does not have a special provision for declaring multi-dimensional arrays, just rather relies on recursion within the type organization to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multi-dimensional array" can be thought of as increasing in row-major order. Multi-dimensional arrays are ordinarily used in numerical algorithms (mainly from applied linear algebra) to store matrices. The construction of the C array is well suited to this particular task. Nevertheless, in early on versions of C the premises 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 assortment with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which accost this issue.

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

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

Array–pointer interchangeability [edit]

The subscript annotation ten[i] (where ten designates a pointer) is syntactic carbohydrate for *(x+i).^[36] Taking reward of the compiler's knowledge of the pointer type, the accost that ten + i points to is not the base address (pointed to by x) incremented past i bytes, but rather is defined to be the base accost incremented by i multiplied by the size of an element that x points to. Thus, ten[i] designates the i+1thursday chemical element of the array.

Furthermore, in nigh expression contexts (a notable exception is as operand of sizeof), an expression of assortment type is automatically converted to a arrow to the array'south showtime element. This implies that an array is never copied equally a whole when named as an argument to a role, only rather only the address of its first element is passed. Therefore, although function calls in C utilize laissez passer-by-value semantics, arrays are in consequence passed past reference.

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

Memory management [edit]

Ane of the most important functions of a programming language is to provide facilities for managing retention and the objects that are stored in retentivity. C provides iii distinct ways to classify retention for objects:^[31]

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

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

Where possible, automatic or static allocation is commonly simplest considering the storage is managed past the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. Still, many information structures can alter in size at runtime, and since static allocations (and automatic allocations before C99) must have a fixed size at compile-fourth dimension, 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 example of dynamically allocated arrays.) Dissimilar automatic resource allotment, which can fail at run time with uncontrolled consequences, the dynamic resource allotment functions return an indication (in the form of a null pointer value) when the required storage cannot be allocated. (Static allotment that is also large is unremarkably detected by the linker or loader, before the program tin even begin execution.)

Unless otherwise specified, static objects contain nada or null pointer values upon program startup. Automatically and dynamically allocated objects are initialized but if an initial value is explicitly specified; otherwise they initially have indeterminate values (typically, whatever flake pattern happens to be present in the storage, which might not even represent a valid value for that type). If the plan attempts to access an uninitialized value, the results are undefined. Many modern compilers attempt to find and warn near this trouble, but both simulated positives and simulated negatives can occur.

Heap retentivity allocation has to exist synchronized with its bodily usage in any programme to be reused as much equally possible. For example, if the only arrow to a heap memory resource allotment goes out of scope or has its value overwritten before it is deallocated explicitly, then that retention cannot exist recovered for afterwards reuse and is substantially lost to the programme, a phenomenon known as a retention leak. Conversely, it is possible for retention to be freed, but is referenced subsequently, leading to unpredictable results. Typically, the failure symptoms appear in a portion of the program unrelated to the code that causes the error, making it difficult to diagnose the failure. Such issues are ameliorated in languages with automated garbage collection.

Libraries [edit]

The C programming language uses libraries as its primary 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 independent within the library that may be used by a program, and declarations of special information types and macro symbols used with these functions. In order for a program 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 (due east.g., -lm, autograph for "link the math library").^[31]

The nearly 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 but a subset of the standard library). This library supports stream input and output, retentivity allocation, mathematics, character strings, and fourth dimension values. Several separate standard headers (for example, stdio.h) specify the interfaces for these and other standard library facilities.

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

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

File handling and streams [edit]

File input and output (I/O) is non office of the C language itself only instead is handled by libraries (such as the C standard library) and their associated header files (e.g. stdio.h). File handling is generally implemented through high-level I/O which works through streams. A stream is from this perspective a information flow that is independent of devices, while a file is a concrete device. The high-level I/O is done through the clan of a stream to a file. In the C standard library, a buffer (a retention surface area or queue) is temporarily used to shop data before it'due south sent to the final destination. This reduces the fourth dimension spent waiting for slower devices, for example a hard drive or solid land drive. Low-level I/O functions are not office of the standard C library^{[ clarification needed ]} just are mostly part of "bare metal" programming (programming that'south independent of any operating system such as about 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 observe and prepare statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided by the compiler. The tool lint was the commencement such, leading to many others.

Automatic source code checking and auditing are beneficial in any language, and for C many such tools exist, such as Lint. A common practice is to use Lint to discover questionable code when a program is outset written. In one case a programme passes Lint, information technology is and then compiled using the C compiler. Also, many compilers can optionally warn virtually syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary prepare of guidelines to avert such questionable code, developed for embedded systems.^[37]

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

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

Uses [edit]

The C Programming Language

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

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

A upshot of C'southward wide availability and efficiency is that compilers, libraries and interpreters of other programming languages are often 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, because the layer of abstraction from hardware is thin, and its overhead is low, an important benchmark for computationally intensive programs. For example, the GNU Multiple Precision Arithmetic Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.

C is sometimes used equally an intermediate language by implementations of other languages. This approach may be used for portability or convenience; past 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 stop of initializer lists, that back up compilation of generated code. However, some of C's shortcomings have prompted the development of other C-based languages specifically designed for use equally intermediate languages, such equally C--.

C has as well been widely used to implement terminate-user applications. Nevertheless, such applications tin too exist written in newer, higher-level languages.

[edit]

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

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

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

When object-oriented programming languages became popular, C++ and Objective-C were two different extensions of C that provided object-oriented capabilities. Both languages were originally implemented as source-to-source compilers; source code was translated into C, and and so 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-similar 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 nearly of C, with a few exceptions.

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

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

Notes [edit]

^ The original example lawmaking volition compile on well-nigh modern compilers that are not in strict standard compliance manner, but it does not fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic message be produced.
^ The master function actually has two arguments, int argc and char *argv[], respectively, which tin be used to handle control line arguments. The ISO C standard (section 5.ane.2.2.1) requires both forms of main to be supported, which is special treatment not afforded to whatever other function.

References [edit]

^ ^a ^b Kernighan, Brian Westward.; Ritchie, Dennis M. (Feb 1978). The C Programming Linguistic communication (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-xiii-110163-0.
^ Ritchie (1993): "Thompson had made a brief endeavor to produce a organization coded in an early version of C—earlier structures—in 1972, just gave up the effort."
^ Fruderica (December 13, 2020). "History of C". The cppreference.com. Archived from the original on Oct 24, 2020. Retrieved Oct 24, 2020.
^ Ritchie (1993): "The scheme of type limerick adopted by C owes considerable debt to Algol 68, although it did not, perhaps, sally in a course that Algol's adherents would corroborate of."
^ Ring Team (October 23, 2021). "The Ring programming linguistic communication and other languages". ring-lang.internet.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Research School of Information science at the Australian National University. June 3, 2010. Archived from the original (PDF) on November six, 2013. Retrieved August 19, 2013. 1980s: ; Verilog first introduced ; Verilog inspired by the C programming linguistic communication
^ ^a ^b ^c ^d ^e Ritchie (1993)
^ "Programming Language Popularity". 2009. Archived from the original on January sixteen, 2009. Retrieved January xvi, 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 October 7, 2021.
^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on December 12, 2019. Retrieved September 10, 2019.
^ ^a ^b Johnson, Due south. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX System". Bell System Tech. J. 57 (six): 2021–2048. CiteSeerXten.one.1.138.35. doi:10.1002/j.1538-7305.1978.tb02141.x. S2CID 17510065. (Note: The PDF is an OCR browse of the original, and contains a rendering of "IBM 370" every bit "IBM 310".)
^ McIlroy, M. D. (1987). A Inquiry Unix reader: annotated excerpts from the Programmer'south 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 Data Manual (FreeBSD xiii.0 ed.). May xxx, 2011. Archived from the original on January 21, 2021. Retrieved January 15, 2021. [1] Archived January 21, 2021, at the Wayback Machine
^ Kernighan, Brian W.; Ritchie, Dennis Grand. (March 1988). The C Programming Language (2d 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 xiv, 2014.
^ C Integrity. International Organization for Standardization. March xxx, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
^ "JTC1/SC22/WG14 – C". Habitation folio. 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 vii, 2013.
^ "Revised C23 Schedule WG fourteen N 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October 10, 2021.
^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on February 25, 2021. Retrieved July 26, 2011.
^ Harbison, Samuel P.; Steele, Guy L. (2002). C: A Reference Manual (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-9. Contains a BNF grammer for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. three.
^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on December 22, 2017. Retrieved September 16, 2011.
^ Kernighan & Ritchie (1996), pp. 192, 259.
^ "10 Common Programming Mistakes in C++". Cs.ucr.edu. Archived from the original on October 21, 2008. Retrieved June 26, 2009.
^ Schultz, Thomas (2004). C and the 8051 (3rd ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-ane-58961-237-2. Archived from the original on July 29, 2020. Retrieved Feb 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-ix.
^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparing of the Programming Languages C and Pascal". ACM Computing Surveys. fourteen (1): 73–92. doi:10.1145/356869.356872. S2CID 3136859.
^ Kernighan & Ritchie (1996), p. 122.
^ For case, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January 7, 2007. Retrieved August 5, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-Pedagogy PUBLIC COMPANY LIMITED. pp. 225–230. ISBN978-616-08-2740-4.
^ Raymond, Eric S. (October xi, 1996). The New Hacker's Dictionary (3rd ed.). MIT Printing. p. 432. ISBN978-0-262-68092-9. Archived from the original on November 12, 2012. Retrieved August v, 2012.
^ "Homo Page for lint (freebsd Section one)". 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's Sourcebook. The statesA.: Miller Freeman, Inc. November–December 1995.
^ "Using C for CGI Programming". linuxjournal.com. March 1, 2005. Archived from the original on February 13, 2010. Retrieved January 4, 2010.
^ McMillan, Robert (Baronial ane, 2013). "Is Coffee Losing Its Mojo?". Wired. Archived from the original on February 15, 2017. Retrieved March five, 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 calculating : 16th international workshop, LCPC 2003, College Station, TX, Us, October 2-four, 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 two, 2019. Retrieved June ix, 2011.

Sources [edit]

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

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). (iii.61 MB)
comp.lang.c Often Asked Questions
A History of C, by Dennis Ritchie

rollintille1992.blogspot.com

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