C# Read a Specific Line in Text File

General-purpose programming language

C
Major implementations
The C Programming Language ^[1] (frequently referred to equally One thousand&R), the seminal book on C
Paradigm	Multi-paradigm: imperative (procedural), structured
Designed past	Dennis Ritchie
Developer	Dennis Ritchie & Bong Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
First appeared	1972; 50 years ago (1972) ^[2]

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

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

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

A successor to the programming language B, C was originally developed at Bong Labs past Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system.^[7] During the 1980s, C gradually gained popularity. Information technology has become one of the nigh widely used programming languages,^[viii] ^[9] with C compilers from various vendors available for the majority of existing computer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and past the International Organization for Standardization (ISO).

C is an imperative procedural language. It was designed to exist compiled to provide low-level admission to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its depression-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C program written with portability in mind can exist compiled for a wide variety of computer platforms and operating systems with few changes to its source lawmaking.^[10]

Since 2000, C has consistently ranked among the tiptop ii languages in the TIOBE index, a mensurate of the popularity of programming languages.^[11]

Overview [edit]

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

The C language besides exhibits the post-obit characteristics:

The language has a minor, fixed number of keywords, including a total fix of command flow primitives: if/else, for, do/while, while, and switch. User-defined names are not distinguished from keywords by any kind of sigil.
It has a large number of arithmetic, bitwise, and logic operators: +,+=,++,&,||, etc.
More than than one assignment may be performed in a single statement.
Functions:
- Office render values can exist ignored, when not needed.
- Function and data pointers permit advertizing hoc run-time polymorphism.
- Functions may not exist defined within the lexical scope of other functions.
Data typing is static, but weakly enforced; all data has a type, only implicit conversions are possible.
Declaration syntax mimics usage context. C has no "define" 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 past the presence of a parenthesized argument listing.
User-defined (typedef) and chemical compound types are possible.
- Heterogeneous amass information types (struct) allow related data elements to be accessed and assigned as a unit.
- Union is a structure with overlapping members; only the last member stored is valid.
- Assortment indexing is a secondary notation, defined in terms of pointer arithmetics. Different structs, arrays are non showtime-class objects: they cannot be assigned or compared using unmarried congenital-in operators. There is no "assortment" keyword in use or definition; instead, square brackets point arrays syntactically, for example month[xi].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are not a distinct information blazon, but are conventionally implemented as null-terminated graphic symbol arrays.
Low-level access to estimator 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 code file inclusion, and conditional compilation.
At that place is a basic form of modularity: files tin exist compiled separately and linked together, with command over which functions and data objects are visible to other files via static and extern attributes.
Circuitous functionality such equally I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does not include certain features found in other languages (such as object orientation and garbage drove), these can be implemented or emulated, oftentimes through the use of external libraries (due east.g., the GLib Object Organisation or the Boehm garbage collector).

Relations to other languages [edit]

Many later languages take borrowed directly or indirectly from C, including C++, C#, Unix's C shell, D, Go, Coffee, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware description languages).^{[half dozen]} These languages have drawn many of their control structures and other basic features from C. Most of them (Python being a dramatic exception) also express highly like syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that can be radically unlike.

History [edit]

Early developments [edit]

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

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

Thompson desired a programming language to make utilities for the new platform. At first, he tried to make a Fortran compiler, but soon gave upwards the thought. Instead, he created a cutting-down version of the recently adult BCPL systems programming linguistic communication. The official description of BCPL was not bachelor at the fourth dimension,^[12] and Thompson modified the syntax to be less wordy, producing the similar but somewhat simpler B.^[vii] However, few utilities were ultimately written in B because it was too slow, and B could not take reward of PDP-11 features such as byte addressability.

In 1972, Ritchie started to better B, about notably calculation data typing for variables, which resulted in creating a new language C.^[13] The C compiler and some utilities fabricated with information technology were included in Version ii Unix.^[14]

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

The preprocessor was introduced around 1973 at the urging of Alan Snyder and also in recognition of the usefulness of the file-inclusion mechanisms bachelor in BCPL and PL/I. Its original version provided only included files and unproblematic cord replacements: #include and #define of parameterless macros. Soon after that, it was extended, by and large past Mike Lesk and then by John Reiser, to incorporate macros with arguments and conditional compilation.^[seven]

Unix was 1 of the kickoff operating system kernels implemented in a language other than associates. Earlier instances include the Multics system (which was written in PL/I) and Chief 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 ground for several implementations of C on new platforms.^[13]

K&R C [edit]

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language.^[1] This volume, known to C programmers every bit One thousand&R, served for many years equally 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, information technology is as well referred to equally C78.^[15] The second edition of the book^[16] covers the after ANSI C standard, described below.

K&R introduced several language features:

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

Even afterwards the publication of the 1989 ANSI standard, for many years Yard&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 use, and considering carefully written Grand&R C code can be legal Standard C likewise.

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

For example:

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

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

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

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

void functions (i.e., functions with no render value)
functions returning struct or marriage types (rather than pointers)
consignment for struct data types
enumerated types

The large number of extensions and lack of understanding on a standard library, together with the linguistic communication popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization.

ANSI C and ISO C [edit]

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

In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to the IEEE working grouping 1003 to become the footing 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 equally 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 chosen C90. Therefore, the terms "C89" and "C90" refer to the same programming linguistic communication.

ANSI, like 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 procedure was to produce a superset of K&R C, incorporating many of the after introduced unofficial features. The standards committee also included several boosted features such every bit role prototypes (borrowed from C++), void pointers, support for international character sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the way used in C++, the K&R interface connected to be permitted, for compatibility with existing source lawmaking.

C89 is supported by current C compilers, and most modern C code is based on information technology. Any program written just in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, inside its resources limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such equally 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 past either standard-conforming or K&R C-based compilers, the __STDC__ macro can exist used to split the code into Standard and 1000&R sections to forbid the employ on a Grand&R C-based compiler of features bachelor simply in Standard C.

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

C99 [edit]

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

C99 introduced several new features, including inline functions, several new data 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 indicate, support for variadic macros (macros of variable arity), and support for one-line comments start with //, every bit in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.

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

In addition, back up for Unicode identifiers (variable / function names) in the form of escaped characters (e.chiliad. \U0001f431) is at present required. Support for raw Unicode names is optional.

C11 [edit]

In 2007, work began on another revision of the C standard, informally chosen "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 blazon generic macros, anonymous 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 divers as 201112L to indicate that C11 support is available.

C17 [edit]

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

C2x [edit]

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

Embedded C [edit]

Historically, embedded C programming requires nonstandard extensions to the C linguistic communication in lodge to support exotic features such as fixed-point arithmetic, multiple singled-out memory banks, and basic I/O operations.

In 2008, the C Standards Committee published a technical written report extending the C language^[22] to address these issues by providing a common standard for all implementations to attach to. Information technology includes a number of features not available in normal C, such as stock-still-point arithmetic, named accost spaces, and basic I/O hardware addressing.

Syntax [edit]

C has a formal grammer specified past the C standard.^[23] Line endings are mostly non significant in C; however, line boundaries do have significance during the preprocessing phase. Comments may appear either between the delimiters /* and */, or (since C99) following // until the end of the line. Comments delimited by /* and */ practice 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 function definitions. Function definitions, in plough, incorporate declarations and statements. Declarations either define new types using keywords such as struct, spousal relationship, and enum, or assign types to and perhaps reserve storage for new variables, usually by writing the type followed by the variable proper noun. Keywords such as char and int specify congenital-in types. Sections of code are enclosed in braces ({ and }, sometimes called "curly brackets") to limit the scope of declarations and to act equally a unmarried argument for control structures.

As an imperative language, C uses statements to specify actions. The near mutual argument is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; every bit a side upshot 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-menses 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, any or all of which tin exist omitted. intermission and continue tin can exist used to leave the innermost enclosing loop argument 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 case to be executed based on the value of an integer expression.

Expressions can apply a diversity of built-in operators and may contain function calls. The lodge in which arguments to functions and operands to nigh operators are evaluated is unspecified. The evaluations may even be interleaved. Nonetheless, all side furnishings (including storage to variables) will occur before the side by side "sequence point"; sequence points include the stop of each expression argument, and the entry to and return from each function phone call. Sequence points also occur during evaluation of expressions containing sure operators (&&, ||, ?: and the comma operator). This permits a loftier 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 Language: "C, similar any other language, has its blemishes. Some of the operators take the wrong precedence; some parts of the syntax could exist better."^[25] The C standard did not try to correct many of these blemishes, considering of the impact of such changes on already existing software.

Grapheme set up [edit]

The bones C source character set includes the following characters:

Lowercase and majuscule 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 end of a text line; it need non correspond to an actual unmarried character, although for convenience C treats it equally ane.

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

The basic C execution character set contains the same characters, forth with representations for warning, 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, also known as keywords, which are the words that cannot be used for any purposes other than those for which they are predefined:

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

C99 reserved five more words:

_Bool
_Complex
_Imaginary
inline
restrict

C11 reserved seven more words:^[26]

_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert
_Thread_local

Virtually of the recently reserved words begin with an underscore followed past a uppercase letter, considering identifiers of that form were previously reserved by the C standard for apply just by implementations. Since existing plan source lawmaking should non have been using these identifiers, information technology would non be affected when C implementations started supporting these extensions to the programming linguistic communication. Some standard headers do ascertain more convenient synonyms for underscored identifiers. The language previously included a reserved word called entry, but this was seldom implemented, and has at present been removed as a reserved word.^[27]

Operators [edit]

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

arithmetic: +, -, *, /, %
assignment: =
augmented assignment: +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=
bitwise logic: ~, &, |, ^
bitwise shifts: <<, >>
boolean logic: !, &&, ||
conditional evaluation: ? :
equality testing: ==, !=
calling functions: ( )
increase and decrement: ++, --
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 signal assignment, post-obit the precedent of Fortran and PL/I, but different ALGOL and its derivatives. C uses the operator == to test for equality. The similarity between these two operators (consignment and equality) may event in the accidental use of one in identify of the other, and in many cases, the fault does not produce an error message (although some compilers produce warnings). For case, the provisional expression if (a == b + 1) might mistakenly be written as if (a = b + 1), which will exist evaluated every bit truthful if a is non aught after the consignment.^[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 10 & 1 == 0, which must be written every bit (x & 1) == 0 if that is the coder's intent.^[29]

"Hello, world" example [edit]

The "how-do-you-do, world" instance, which appeared in the beginning edition of Thousand&R, has become the model for an introductory program in near programming textbooks. The program prints "hello, globe" to the standard output, which is usually a terminal or screen display.

The original version was:^[30]

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

A standard-befitting "hello, world" plan is:^[a]

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

The first line of the programme 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, equally opposed to double quotes which typically include local or project-specific header files.

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

The opening curly brace indicates the showtime of the definition of the master role.

The next line calls (diverts execution to) a role named printf, which in this case is supplied from a system library. In this phone call, the printf function is passed (provided with) a single argument, the address of the first character in the cord literal "howdy, world\n". The string literal is an unnamed array with elements of blazon char, ready automatically by the compiler with a final 0-valued character to mark the terminate 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 finish of the current line. The render value of the printf part is of blazon int, but information technology is silently discarded since it is not used. (A more careful program might test the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement.

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

Data types [edit]

The type system in C is static and weakly typed, which makes it like to the type arrangement of ALGOL descendants such every bit Pascal.^[32] There 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 single-byte characters. C99 added a boolean datatype. There are likewise derived types including arrays, pointers, records (struct), and unions (union).

C is oft used in low-level systems programming where escapes from the blazon system may exist necessary. The compiler attempts to ensure type correctness of well-nigh expressions, but the developer can override the checks in various ways, either by using a type cast to explicitly convert a value from 1 type to another, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way.

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

C's usual arithmetic conversions allow for efficient code to be generated, but 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 type of reference that records the accost or location of an object or function in memory. Pointers can exist dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can exist manipulated using assignment or pointer arithmetics. The run-time representation of a arrow value is typically a raw memory address (mayhap augmented by an commencement-within-word field), just since a pointer'southward type includes the blazon of the thing pointed to, expressions including pointers can be type-checked at compile time. Pointer arithmetic is automatically scaled past the size of the pointed-to data blazon. 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 information types, such as copse, are normally implemented every bit dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions equally arguments to higher-order functions (such as qsort or bsearch) or as callbacks to be invoked by effect handlers.^[31]

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

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

Careless employ of pointers is potentially dangerous. Because they are typically unchecked, a arrow variable can be made to signal to whatever arbitrary location, which can cause undesirable effects. Although properly used pointers bespeak to safe places, they can be fabricated to betoken to unsafe places past using invalid pointer arithmetic; the objects they betoken to may continue to be used after deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may exist directly assigned an unsafe value using a cast, spousal relationship, or through another corrupt arrow. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more restrictive reference types.

Arrays [edit]

Assortment types in C are traditionally of a fixed, static size specified at compile time. The more contempo C99 standard also allows a course of variable-length arrays. However, it is also possible to allocate a cake of retention (of arbitrary size) at run-time, using the standard library'due south malloc part, and treat it as an array.

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

C does not have a special provision for declaring multi-dimensional arrays, but rather relies on recursion within the type system to declare arrays of arrays, which effectively accomplishes the same thing. The alphabetize values of the resulting "multi-dimensional assortment" can be thought of as increasing in row-major order. Multi-dimensional arrays are commonly used in numerical algorithms (mainly from practical linear algebra) to shop matrices. The structure of the C array is well suited to this item task. However, in early 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 array with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this outcome.

The post-obit example using modernistic C (C99 or afterward) shows allocation of a 2-dimensional array on the heap and the use of multi-dimensional array indexing for accesses (which can use bounds-checking on many C compilers):

                        int                                    func            (            int                                    N            ,                                    int                                    M            )                        {                                                float                                    (            *            p            )[            N            ][            M            ]                                    =                                    malloc            (            sizeof                                    *            p            );                                                if                                    (            !            p            )                                                return                                    -one            ;                                                for                                    (            int                                    i                                    =                                    0            ;                                    i                                    <                                    N            ;                                    i            ++            )                                                for                                    (            int                                    j                                    =                                    0            ;                                    j                                    <                                    1000            ;                                    j            ++            )                                                (            *            p            )[            i            ][            j            ]                                    =                                    i                                    +                                    j            ;                                                print_array            (            N            ,                                    M            ,                                    p            );                                                costless            (            p            );                                                render                                    1            ;                        }

Array–pointer interchangeability [edit]

The subscript notation x[i] (where ten designates a arrow) is syntactic sugar for *(x+i).^[36] Taking advantage of the compiler's knowledge of the pointer type, the address that x + i points to is non the base address (pointed to by x) incremented by i bytes, but rather is divers to exist the base of operations address incremented by i multiplied by the size of an element that x points to. Thus, 10[i] designates the i+1thursday element of the array.

Furthermore, in most expression contexts (a notable exception is every bit operand of sizeof), an expression of array blazon is automatically converted to a pointer to the array's 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 commencement element is passed. Therefore, although function calls in C use pass-by-value semantics, arrays are in upshot passed by reference.

The total size of an array 10 can be determined by applying sizeof to an expression of array type. The size of an chemical element can be determined past applying the operator sizeof to any dereferenced chemical element of an array A, equally in northward = sizeof A[0]. This, the number of elements in a declared assortment A tin can be determined as sizeof A / sizeof A[0]. Note, that if simply a pointer to the first element is bachelor as it is often the example in C lawmaking considering of the automatic conversion described above, the information almost the full blazon of the array and its length are lost.

Memory management [edit]

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

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

These three approaches are appropriate in unlike situations and have various trade-offs. For example, static memory allocation has little allocation overhead, automatic allotment may involve slightly more overhead, and dynamic memory allotment can potentially have a peachy deal of overhead for both allocation and deallocation. The persistent nature of static objects is useful for maintaining state information across function calls, automated allocation is like shooting fish in a barrel to use just stack space is typically much more limited and transient than either static retentiveness or heap infinite, and dynamic retentivity allotment allows convenient resource allotment of objects whose size is known merely at run-time. Most C programs make extensive utilise of all three.

Where possible, automated or static resource allotment is usually simplest because the storage is managed past the compiler, freeing the programmer of the potentially mistake-prone chore of manually allocating and releasing storage. However, many information structures can alter in size at runtime, and since static allocations (and automatic allocations before C99) must have a stock-still 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 example of dynamically allocated arrays.) Different automatic allocation, which can fail at run fourth dimension with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a null pointer value) when the required storage cannot be allocated. (Static allocation that is as well big is ordinarily detected by the linker or loader, earlier the programme can even begin execution.)

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

Heap memory resource allotment has to be synchronized with its actual usage in any plan to exist reused as much equally possible. For example, if the but pointer to a heap memory allotment goes out of scope or has its value overwritten before it is deallocated explicitly, so that retentiveness cannot be recovered for afterwards reuse and is essentially lost to the programme, a phenomenon known as a memory leak. Conversely, it is possible for memory to be freed, but is referenced later, leading to unpredictable results. Typically, the failure symptoms appear in a portion of the plan unrelated to the code that causes the mistake, making it difficult to diagnose the failure. Such issues are ameliorated in languages with automatic garbage collection.

Libraries [edit]

The C programming language uses libraries as its primary method of extension. In C, a library is a set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a programme, and declarations of special data types and macro symbols used with these functions. In order for a program to utilize a library, it must include the library'south header file, and the library must be linked with the plan, which in many cases requires compiler flags (due east.g., -lm, shorthand for "link the math library").^[31]

The most mutual 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 limited environments such every bit embedded systems may provide only a subset of the standard library). This library supports stream input and output, memory allocation, mathematics, graphic symbol strings, and time values. Several carve up standard headers (for instance, 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-similar systems, particularly 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 accept been written in C, at that place are a wide diversity of other libraries available. Libraries are frequently written in C because C compilers generate efficient object code; programmers then create interfaces to the library so that the routines tin exist used from higher-level languages like Coffee, Perl, and Python.^[31]

File handling and streams [edit]

File input and output (I/O) is non role of the C linguistic communication itself but instead is handled by libraries (such as the C standard library) and their associated header files (due east.thousand. 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 contained of devices, while a file is a concrete device. The loftier-level I/O is done through the clan of a stream to a file. In the C standard library, a buffer (a memory area or queue) is temporarily used to store data earlier it's sent to the terminal destination. This reduces the time spent waiting for slower devices, for example a hard drive or solid land drive. Depression-level I/O functions are not part of the standard C library^{[ clarification needed ]} but are mostly part of "bare metallic" programming (programming that's independent of any operating organization such as most embedded programming). With few exceptions, implementations include low-level I/O.

Language tools [edit]

A number of tools take been adult to aid C programmers find and fix statements with undefined behavior or mayhap erroneous expressions, with greater rigor than that provided by the compiler. The tool lint was the beginning such, leading to many others.

Automatic source code checking and auditing are benign in any linguistic communication, and for C many such tools exist, such every bit Lint. A common practice is to use Lint to detect questionable lawmaking when a plan is first written. Once a program passes Lint, it is and so compiled using the C compiler. Also, many compilers tin optionally warn about syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary gear up of guidelines to avoid such questionable code, adult for embedded systems.^[37]

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

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

Uses [edit]

The C Programming Linguistic communication

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

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

A event of C's 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, Cherry, 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 criterion for computationally intensive programs. For example, the GNU Multiple Precision Arithmetic Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.

C is sometimes used as an intermediate language by implementations of other languages. This approach may exist used for portability or convenience; by using C every bit an intermediate language, additional automobile-specific code generators are not necessary. C has some features, such every bit line-number preprocessor directives and optional superfluous commas at the cease 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 utilize equally intermediate languages, such as C--.

C has besides been widely used to implement end-user applications. However, such applications can also 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 later languages such every bit C#, D, Go, Coffee, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix'due south C trounce.^[42] The nigh 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 large-scale program structures that differ from those of C, sometimes radically.

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

When object-oriented programming languages became pop, C++ and Objective-C were two unlike 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 language (originally named "C with Classes") was devised by Bjarne Stroustrup as an arroyo to providing object-oriented functionality with a C-like syntax.^[44] C++ adds greater typing forcefulness, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Most 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 function calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk.

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

Run into as well [edit]

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

Notes [edit]

^ The original example code will compile on near modern compilers that are not in strict standard compliance way, only it does not fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic bulletin be produced.
^ The main role actually has 2 arguments, int argc and char *argv[], respectively, which can be used to handle command line arguments. The ISO C standard (department 5.1.ii.2.ane) requires both forms of main to be supported, which is special treatment not afforded to any other function.

References [edit]

^ ^a ^b Kernighan, Brian Due west.; Ritchie, Dennis M. (February 1978). The C Programming Linguistic communication (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110163-0.
^ Ritchie (1993): "Thompson had made a brief attempt to produce a system coded in an early version of C—earlier structures—in 1972, but gave upward the effort."
^ Fruderica (December 13, 2020). "History of C". The cppreference.com. Archived from the original on October 24, 2020. Retrieved October 24, 2020.
^ Ritchie (1993): "The scheme of type composition adopted by C owes considerable debt to Algol 68, although it did not, perchance, emerge in a course that Algol's adherents would approve of."
^ Ring Team (October 23, 2021). "The Ring programming language and other languages". band-lang.cyberspace.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Research School of Computer science at the Australian National University. June 3, 2010. Archived from the original (PDF) on November 6, 2013. Retrieved August nineteen, 2013. 1980s: ; Verilog start introduced ; Verilog inspired by the C programming language
^ ^a ^b ^c ^d ^e Ritchie (1993)
^ "Programming Language Popularity". 2009. Archived from the original on January 16, 2009. Retrieved January sixteen, 2009.
^ "TIOBE Programming Community Alphabetize". 2009. Archived from the original on May 4, 2009. Retrieved May vi, 2009.
^ ^a ^b "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
^ "TIOBE Index for Oct 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, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX System". Bell Organisation 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 Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. p. 10. 139. Archived (PDF) from the original on November 11, 2017. Retrieved February 1, 2015.
^ "C manual pages". FreeBSD Miscellaneous Information Manual (FreeBSD 13.0 ed.). May thirty, 2011. Archived from the original on Jan 21, 2021. Retrieved Jan 15, 2021. [1] Archived Jan 21, 2021, at the Wayback Car
^ Kernighan, Brian W.; Ritchie, Dennis M. (March 1988). The C Programming Language (second ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-thirteen-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 Organisation for Standardization. March 30, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
^ "JTC1/SC22/WG14 – C". Domicile folio. ISO/IEC. Archived from the original on Feb 12, 2018. Retrieved June two, 2011.
^ Andrew Binstock (October 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on Baronial two, 2013. Retrieved September 7, 2013.
^ "Revised C23 Schedule WG 14 Northward 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved Oct 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 Transmission (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-ix. Contains a BNF grammer for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. iii.
^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on Dec 22, 2017. Retrieved September xvi, 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 (tertiary ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-1-58961-237-2. Archived from the original on July 29, 2020. Retrieved February 10, 2012.
^ Kernighan & Ritchie (1978), p. 6.
^ ^a ^b ^c ^d ^east ^f ^{one thousand} 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 Computing Surveys. 14 (1): 73–92. doi:ten.1145/356869.356872. S2CID 3136859.
^ Kernighan & Ritchie (1996), p. 122.
^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January vii, 2007. Retrieved Baronial 5, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-Teaching PUBLIC COMPANY LIMITED. pp. 225–230. ISBN978-616-08-2740-4.
^ Raymond, Eric S. (Oct 11, 1996). The New Hacker's Lexicon (3rd ed.). MIT Press. p. 432. ISBN978-0-262-68092-9. Archived from the original on Nov 12, 2012. Retrieved Baronial 5, 2012.
^ "Homo Page for lint (freebsd Department 1)". unix.com. May 24, 2001. Retrieved July 15, 2014.
^ Dale, Nell B.; Weems, Fleck (2014). Programming and problem solving with C++ (sixth ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
^ Dr. Dobb'southward Sourcebook. UsA.: Miller Freeman, Inc. November–December 1995.
^ "Using C for CGI Programming". linuxjournal.com. March 1, 2005. Archived from the original on February thirteen, 2010. Retrieved Jan 4, 2010.
^ McMillan, Robert (Baronial i, 2013). "Is Java Losing Its Mojo?". Wired. Archived from the original on February xv, 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, Oct 2-4, 2003 : revised papers. Springer. ISBN978-3540246442. OCLC 57965544.
^ Stroustrup, Bjarne (1993). "A History of C++: 1979−1991" (PDF). Archived (PDF) from the original on February 2, 2019. Retrieved June 9, 2011.

Sources [edit]

Ritchie, Dennis K. (March 1993). "The Development of the C Language". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:x.1145/155360.155580.
Ritchie, Dennis Thousand. (1993). "The Development of the C Language". The 2nd ACM SIGPLAN Conference on History of Programming Languages (HOPL-2). ACM. pp. 201–208. doi:ten.1145/154766.155580. ISBN0-89791-570-4 . Retrieved November iv, 2014.
Kernighan, Brian W.; Ritchie, Dennis M. (1996). The C Programming Language (2d ed.). Prentice Hall. ISBN7-302-02412-10.

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 Frequently Asked Questions
A History of C, by Dennis Ritchie

sullivanrectelon1981.blogspot.com

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