C# Reading a Text File Into Separate List

General-purpose programming language

C
Major implementations
The C Programming Language ^[one] (often referred to as K&R), the seminal book on C
Paradigm	Multi-prototype: imperative (procedural), structured
Designed past	Dennis Ritchie
Developer	Dennis Ritchie & Bell Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C)
First appeared	1972; l years ago (1972) ^[2]

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

Typing subject	Static, weak, manifest, nominal
OS	Cross-platform
Filename extensions	.c, .h
Website	world wide web.iso.org/standard/74528.html world wide web.open-std.org/jtc1/sc22/wg14/
pcc, GCC, Clang, Intel C, C++Builder, Microsoft Visual C++, Watcom C
Dialects
Cyclone, Unified Parallel C, Split-C, Cilk, C*
Influenced by
B (BCPL, CPL), ALGOL 68,^[4] associates, 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),^[6] Nim, Zig
C Programming at Wikibooks

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

A successor to the programming language B, C was originally developed at Bell Labs past Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. It was practical to re-implementing the kernel of the Unix operating system.^[vii] During the 1980s, C gradually gained popularity. It has go 1 of the nearly widely used programming languages,^[eight] ^[9] with C compilers from diverse vendors available for the majority of existing computer architectures and operating systems. C has been standardized past ANSI since 1989 (ANSI C) and by the International Organization for Standardization (ISO).

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

Since 2000, C has consistently ranked among the top two languages in the TIOBE alphabetize, a measure of the popularity of programming languages.^[11]

Overview

Like virtually procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type organization prevents unintended operations. In C, all executable code is contained inside subroutines (as well called "functions", though not strictly in the sense of functional programming). Function parameters are e'er passed by value (except arrays). Pass-by-reference is fake in C by explicitly passing arrow values. C plan source text is free-format, using the semicolon equally a statement terminator and curly braces for grouping blocks of statements.

The C language likewise exhibits the following characteristics:

The language has a small-scale, fixed number of keywords, including a full set of control menstruum primitives: if/else, for, do/while, while, and switch. User-defined names are not distinguished from keywords past any kind of sigil.
It has a large number of arithmetics, bitwise, and logic operators: +,+=,++,&,||, etc.
More than than ane consignment may be performed in a single statement.
Functions:
- Function return values can exist ignored, when non needed.
- Function and data pointers permit ad hoc run-time polymorphism.
- Functions may not be defined within the lexical telescopic of other functions.
Data typing is static, but weakly enforced; all information has a type, merely implicit conversions are possible.
Proclamation syntax mimics usage context. C has no "define" keyword; instead, a statement kickoff with the name of a blazon is taken as a declaration. In that location is no "function" keyword; instead, a part is indicated by the presence of a parenthesized argument list.
User-defined (typedef) and chemical compound types are possible.
- Heterogeneous amass data types (struct) let related information elements to be accessed and assigned as a unit.
- Matrimony is a structure with overlapping members; only the last member stored is valid.
- Array indexing is a secondary notation, defined in terms of pointer arithmetics. Dissimilar structs, arrays are not start-course objects: they cannot be assigned or compared using unmarried congenital-in operators. There is no "array" keyword in use or definition; instead, square brackets indicate arrays syntactically, for example month[11].
- Enumerated types are possible with the enum keyword. They are freely interconvertible with integers.
- Strings are not a distinct data type, simply are conventionally implemented as null-terminated graphic symbol arrays.
Low-level access to computer memory is possible by converting machine addresses to typed pointers.
Procedures (subroutines not 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.
There is a basic form of modularity: files can be compiled separately and linked together, with control over which functions and information objects are visible to other files via static and extern attributes.
Complex functionality such as I/O, string manipulation, and mathematical functions are consistently delegated to library routines.

While C does non include certain features found in other languages (such as object orientation and garbage drove), these tin can exist implemented or emulated, often through the utilize of external libraries (e.chiliad., the GLib Object Organization or the Boehm garbage collector).

Relations to other languages

Many afterward languages take borrowed directly or indirectly from C, including C++, C#, Unix's C crush, D, Go, Java, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware clarification languages).^{[half dozen]} These languages take drawn many of their control structures and other basic features from C. Virtually of them (Python beingness a dramatic exception) also express highly similar 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 tin be radically dissimilar.

History

Early developments

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

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

Thompson desired a programming language to make utilities for the new platform. At first, he tried to brand a Fortran compiler, merely before long gave upwards the thought. Instead, he created a cut-downwards version of the recently adult BCPL systems programming language. The official description of BCPL was non available at the time,^[12] and Thompson modified the syntax to be less wordy, producing the similar but somewhat simpler B.^[7] However, few utilities were ultimately written in B because it was too irksome, and B could non take advantage of PDP-11 features such equally byte addressability.

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

At Version 4 Unix, released in November 1973, the Unix kernel was extensively re-implemented in C.^[seven] By this time, the C linguistic communication had acquired some powerful features such as struct types.

The preprocessor was introduced around 1973 at the urging of Alan Snyder and also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I. Its original version provided simply included files and elementary string replacements: #include and #define of parameterless macros. Soon after that, it was extended, by and large by Mike Lesk and then by John Reiser, to comprise macros with arguments and provisional compilation.^[7]

Unix was one of the first operating system kernels implemented in a language other than assembly. Earlier instances include the Multics organization (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 linguistic communication to facilitate portability of the Unix operating system. Johnson'due south Portable C Compiler served as the basis for several implementations of C on new platforms.^[13]

K&R C

In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Linguistic communication.^[1] This book, known to C programmers as G&R, served for many years every bit an informal specification of the language. The version of C that it describes is usually referred to as "K&R C". As this was released in 1978, it is besides referred to equally C78.^[15] The second edition of the book^[16] covers the later ANSI C standard, described beneath.

Thou&R introduced several linguistic communication features:

Standard I/O library
long int data blazon
unsigned int data type
Chemical compound consignment operators of the form =op (such as =-) were inverse to the course op= (that is, -=) to remove the semantic ambiguity created by constructs such as i=-10, which had been interpreted as i =- x (decrement i by 10) instead of the perhaps intended i = -10 (allow i be −10).

Even subsequently the publication of the 1989 ANSI standard, for many years K&R C was however considered the "everyman mutual denominator" to which C programmers restricted themselves when maximum portability was desired, since many older compilers were yet in use, and because advisedly written 1000&R C code can exist legal Standard C equally well.

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

For example:

                        long                                    some_function            ();                        /* int */                                    other_function            ();                        /* int */                                    calling_function            ()                        {                                                long                                    test1            ;                                                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 later standards.

Since K&R function declarations did not include any information near role arguments, function parameter blazon checks were non performed, although some compilers would event a alert message if a local function was called with the wrong number of arguments, or if multiple calls to an external role used different numbers or types of arguments. Separate tools such equally Unix's lint utility were developed that (among other things) could cheque for consistency of function use beyond 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 detail PCC^[17]) and some other vendors. These included:

void functions (i.east., functions with no return 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 agreement on a standard library, together with the linguistic communication popularity and the fact that not even the Unix compilers precisely implemented the Thousand&R specification, led to the necessity of standardization.

ANSI C and ISO C

During the tardily 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 committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the not-portable portion of the Unix C library was handed off to the IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Language C". This version of the linguistic communication is often referred to as ANSI C, Standard C, or sometimes C89.

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

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

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

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

In cases where lawmaking must be compilable by either standard-conforming or 1000&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and Thousand&R sections to prevent the apply on a K&R C-based compiler of features bachelor only in Standard C.

Subsequently 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 right some details and to add more extensive back up for international graphic symbol sets.^[18]

C99

The C standard was further revised in the tardily 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to equally "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 complex type to represent complex numbers), variable-length arrays and flexible array members, improved back up for IEEE 754 floating point, support for variadic macros (macros of variable arity), and back up for one-line comments offset with //, as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.

C99 is for the almost part astern uniform with C90, but is stricter in some ways; in particular, a annunciation 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 bachelor. GCC, Solaris Studio, and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++, however, implements the C89 standard and those parts of C99 that are required for compatibility with C++11.^[20] ^{[ needs update ]}

In addition, back up for Unicode identifiers (variable / role names) in the form of escaped characters (e.g. \U0001f431) is now required. Back up for raw Unicode names is optional.

C11

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

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

C17

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

C2x

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

Embedded C

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

In 2008, the C Standards Commission published a technical study extending the C language^[22] to address these problems by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as stock-still-bespeak arithmetic, named address spaces, and basic I/O hardware addressing.

Syntax

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

C source files comprise declarations and office definitions. Function definitions, in turn, incorporate declarations and statements. Declarations either define new types using keywords such every bit struct, matrimony, and enum, or assign types to and perhaps reserve storage for new variables, commonly past writing the type followed past the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }, sometimes called "curly brackets") to limit the telescopic of declarations and to human activity as a single statement for control structures.

As an imperative language, C uses statements to specify deportment. The almost common statement is an expression statement, consisting of an expression to exist evaluated, followed by a semicolon; as a side event of the evaluation, functions may exist called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several command-menstruum statements identified by reserved keywords. Structured programming is supported past 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 can exist omitted. break and keep can be used to leave the innermost enclosing loop statement or skip to its reinitialization. In that location is also a not-structured goto argument 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 tin utilise a variety of congenital-in operators and may contain function calls. The social club in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side furnishings (including storage to variables) will occur earlier the next "sequence indicate"; sequence points include the finish of each expression statement, and the entry to and return from each part call. Sequence points too occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a high degree of object lawmaking optimization by the compiler, just requires C programmers to take more care to obtain reliable results than is needed for other programming languages.

Kernighan and Ritchie say in the Introduction of The C Programming Language: "C, like any 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 attempt to correct many of these blemishes, because of the touch of such changes on already existing software.

Graphic symbol gear up

The basic C source grapheme set includes the following characters:

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

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

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

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

Reserved words

C89 has 32 reserved words, also known every bit keywords, which are the words that cannot be used for whatsoever purposes other than those for which they are predefined:

car
break
case
char
const
keep
default
exercise
double
else
enum
extern
float
for
goto
if
int
long
register
return
short
signed
sizeof
static
struct
switch
typedef
spousal relationship
unsigned
void
volatile
while

C99 reserved 5 more words:

_Bool
_Complex
_Imaginary
inline
restrict

C11 reserved seven more words:^[26]

_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert
_Thread_local

Well-nigh of the recently reserved words brainstorm with an underscore followed by a uppercase letter of the alphabet, because identifiers of that form were previously reserved by the C standard for apply merely by implementations. Since existing program source lawmaking should not have been using these identifiers, information technology would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers exercise 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

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

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

C uses the operator = (used in mathematics to express equality) to bespeak assignment, post-obit the precedent of Fortran and PL/I, but unlike ALGOL and its derivatives. C uses the operator == to test for equality. The similarity betwixt these two operators (assignment and equality) may result in the accidental use of i in place of the other, and in many cases, the error does not produce an error message (although some compilers produce warnings). For case, the conditional expression if (a == b + 1) might mistakenly be written equally if (a = b + ane), which volition exist evaluated as true if a is not zero afterward the assignment.^[28]

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

"Hello, world" example

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

The original version was:^[xxx]

                        chief            ()                        {                                                printf            (            "hi, globe            \n            "            );                        }

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

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

The first line of the program contains a preprocessing directive, indicated by #include. This causes the compiler to supercede 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 bending brackets surrounding stdio.h bespeak that stdio.h is located using a search strategy that prefers headers provided with the compiler to other headers having the same name, as opposed to double quotes which typically include local or project-specific header files.

The next line indicates that a function named main is being defined. The chief function serves a special purpose in C programs; the run-fourth dimension environment calls the primary function to begin program execution. The type specifier int indicates that the value that is returned to the invoker (in this instance the run-time environment) every bit a upshot of evaluating the main 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 starting time of the definition of the main function.

The next line calls (diverts execution to) a function named printf, which in this instance is supplied from a system library. In this call, the printf role is passed (provided with) a single statement, the address of the first character in the string literal "how-do-you-do, world\n". The cord literal is an unnamed array with elements of type char, set automatically by the compiler with a final 0-valued character to marker the end of the assortment (printf needs to know this). The \n is an escape sequence that C translates to a newline character, which on output signifies the terminate of the electric current line. The return value of the printf part is of blazon int, only 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 office succeeded.) The semicolon ; terminates the statement.

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

Information types

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

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

Some find C's declaration syntax unintuitive, peculiarly for part pointers. (Ritchie's thought was to declare identifiers in contexts resembling their use: "declaration reflects use".)^[33]

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

Pointers

C supports the utilise of pointers, a blazon of reference that records the address or location of an object or office in memory. Pointers tin be dereferenced to access information stored at the address pointed to, or to invoke a pointed-to function. Pointers tin be manipulated using assignment or pointer arithmetic. The run-time representation of a arrow value is typically a raw memory address (perhaps augmented past an offset-inside-give-and-take field), but since a pointer's type includes the blazon of the thing pointed to, expressions including pointers can exist type-checked at compile time. Pointer arithmetic is automatically scaled by the size of the pointed-to data type. Pointers are used for many purposes in C. Text strings are unremarkably manipulated using pointers into arrays of characters. Dynamic memory resource allotment is performed using pointers. Many data types, such as trees, are commonly implemented equally dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to college-society functions (such as qsort or bsearch) or equally callbacks to be invoked by event handlers.^[31]

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

Void pointers (void *) point to objects of unspecified type, and tin therefore exist used equally "generic" data pointers. Since the size and type 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 arrow type.^[31]

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

Arrays

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

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

C does not take a special provision for declaring multi-dimensional arrays, merely rather relies on recursion inside the type system to declare arrays of arrays, which effectively accomplishes the same matter. The alphabetize values of the resulting "multi-dimensional array" tin can be thought of equally increasing in row-major lodge. Multi-dimensional arrays are commonly used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C assortment is well suited to this particular task. However, in early on versions of C the bounds of the array must be known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this was to allocate the array with an boosted "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which accost this effect.

The following example using mod C (C99 or later) shows allotment of a ii-dimensional array on the heap and the utilize of multi-dimensional array indexing for accesses (which tin apply premises-checking on many C compilers):

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

Array–arrow interchangeability

The subscript notation ten[i] (where ten designates a pointer) is syntactic sugar for *(x+i).^[36] Taking advantage of the compiler'due south knowledge of the pointer type, the accost that 10 + i points to is non the base address (pointed to past x) incremented by i bytes, merely rather is defined to be the base address incremented past i multiplied by the size of an element that x points to. Thus, ten[i] designates the i+1th element of the array.

Furthermore, in most expression contexts (a notable exception is equally operand of sizeof), an expression of assortment type is automatically converted to a pointer to the array'due south first element. This implies that an array is never copied every bit a whole when named as an argument to a role, just rather but the accost of its first element is passed. Therefore, although part calls in C utilize pass-by-value semantics, arrays are in effect passed by reference.

The full size of an assortment x can be determined past applying sizeof to an expression of array type. The size of an element can be adamant by applying the operator sizeof to any dereferenced element of an array A, as in n = sizeof A[0]. This, the number of elements in a alleged assortment A tin be determined as sizeof A / sizeof A[0]. Annotation, that if only a pointer to the first element is available as information technology is often the case in C code because of the automated conversion described higher up, the information about the full blazon of the assortment and its length are lost.

Retentiveness direction

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

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

These iii approaches are appropriate in different situations and have various trade-offs. For instance, static memory allocation has little allocation overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially take a great deal of overhead for both allocation and deallocation. The persistent nature of static objects is useful for maintaining state information across part calls, automated allocation is easy to utilise but stack space is typically much more limited and transient than either static memory or heap space, and dynamic memory allotment allows user-friendly allocation of objects whose size is known only at run-fourth dimension. Most C programs make extensive use of all three.

Where possible, automatic or static allocation is usually simplest because the storage is managed by the compiler, freeing the developer of the potentially error-prone task of manually allocating and releasing storage. However, many data structures can modify in size at runtime, and since static allocations (and automated allocations earlier C99) must have a fixed size at compile-time, there are many situations in which dynamic allocation is necessary.^[31] Prior to the C99 standard, variable-sized arrays were a common example of this. (See the article on malloc for an case of dynamically allocated arrays.) Unlike automatic allocation, which tin neglect at run fourth dimension with uncontrolled consequences, the dynamic resource allotment functions return an indication (in the class of a null pointer value) when the required storage cannot exist allocated. (Static allotment that is besides large is ordinarily detected by the linker or loader, before the program can fifty-fifty begin execution.)

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

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

Libraries

The C programming language uses libraries as its primary method of extension. In C, a library is a set of functions independent within a single "annal" file. Each library typically has a header file, which contains the prototypes of the functions contained inside the library that may be used by a program, and declarations of special data types and macro symbols used with these functions. In order for a programme to employ a library, it must include the library's header file, and the library must be linked with the program, which in many cases requires compiler flags (e.1000., -lm, shorthand for "link the math library").^[31]

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

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

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

File treatment and streams

File input and output (I/O) is not function of the C language itself only instead is handled by libraries (such as the C standard library) and their associated header files (e.thou. 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 physical device. The loftier-level I/O is done through the association of a stream to a file. In the C standard library, a buffer (a retentiveness area or queue) is temporarily used to store data before it'south sent to the final destination. This reduces the time spent waiting for slower devices, for example a difficult drive or solid state drive. Low-level I/O functions are not role of the standard C library^{[ clarification needed ]} but are generally office of "bare metal" programming (programming that'due south independent of any operating arrangement such as most embedded programming). With few exceptions, implementations include low-level I/O.

Language tools

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

Automated source code checking and auditing are beneficial in whatever linguistic communication, and for C many such tools be, such as Lint. A mutual do is to use Lint to observe questionable code when a program is first written. Once a program passes Lint, it is and so compiled using the C compiler. Also, many compilers can optionally warn almost syntactically valid constructs that are probable to actually be errors. MISRA C is a proprietary set of guidelines to avert such questionable lawmaking, developed for embedded systems.^[37]

There are also compilers, libraries, and operating organization level mechanisms for performing actions that are non a standard role of C, such as bounds checking for arrays, detection of buffer overflow, serialization, dynamic retentiveness tracking, and automatic garbage drove.

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

Uses

The C Programming Language

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

C tin 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 called over interpreted languages because of its speed, stability, and nigh-universal availability.^[40]

A outcome of C'south 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, considering 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 Arithmetics Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.

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

C has also been widely used to implement finish-user applications. Even so, such applications can likewise be written in newer, college-level languages.

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 as C#, D, Go, Java, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix'southward C crush.^[42] The nigh pervasive influence has been syntactical; all of the languages mentioned combine the statement and (more than or less recognizably) expression syntax of C with blazon systems, information models, and/or large-calibration programme structures that differ from those of C, sometimes radically.

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

When object-oriented programming languages became pop, 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 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 forcefulness, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Near a superset of C, C++ at present supports most 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 image. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations, and function calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk.

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

Notes

^ The original example code volition compile on almost modern compilers that are not in strict standard compliance way, but it does not fully accommodate to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic bulletin be produced.
^ The main function really has two arguments, int argc and char *argv[], respectively, which tin be used to handle control line arguments. The ISO C standard (section v.1.2.2.ane) requires both forms of main to be supported, which is special treatment not afforded to any other function.

References

^ ^a ^b Kernighan, Brian W.; Ritchie, Dennis K. (February 1978). The C Programming Language (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-thirteen-110163-0.
^ Ritchie (1993): "Thompson had made a brief attempt to produce a system coded in an early version of C—before structures—in 1972, but gave upwards the try."
^ Fruderica (December xiii, 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, maybe, sally in a form that Algol'southward adherents would approve of."
^ Ring Team (Oct 23, 2021). "The Band programming linguistic communication and other languages". band-lang.cyberspace.
^ ^a ^b "Verilog HDL (and C)" (PDF). The Research Schoolhouse of Computer Science at the Australian National University. June iii, 2010. Archived from the original (PDF) on November 6, 2013. Retrieved Baronial xix, 2013. 1980s: ; Verilog first introduced ; Verilog inspired past the C programming linguistic communication
^ ^a ^b ^c ^d ^eastward Ritchie (1993)
^ "Programming Linguistic communication Popularity". 2009. Archived from the original on January 16, 2009. Retrieved Jan 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 Dec 12, 2019. Retrieved September 10, 2019.
^ ^a ^b Johnson, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX Arrangement". Bong Organization Tech. J. 57 (6): 2021–2048. CiteSeerX10.1.1.138.35. doi:10.1002/j.1538-7305.1978.tb02141.x. S2CID 17510065. (Note: The PDF is an OCR scan of the original, and contains a rendering of "IBM 370" as "IBM 310".)
^ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer'south Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. p. 10. 139. Archived (PDF) from the original on November 11, 2017. Retrieved February i, 2015.
^ "C transmission pages". FreeBSD Miscellaneous Information Manual (FreeBSD thirteen.0 ed.). May 30, 2011. Archived from the original on January 21, 2021. Retrieved January xv, 2021. [1] Archived Jan 21, 2021, at the Wayback Machine
^ Kernighan, Brian W.; Ritchie, Dennis K. (March 1988). The C Programming Language (2nd ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-thirteen-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 April 14, 2014.
^ C Integrity. International Organization for Standardization. March thirty, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
^ "JTC1/SC22/WG14 – C". Home page. ISO/IEC. Archived from the original on February 12, 2018. Retrieved June 2, 2011.
^ Andrew Binstock (October 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on August 2, 2013. Retrieved September 7, 2013.
^ "Revised C23 Schedule WG 14 N 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved October x, 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 50. (2002). C: A Reference Manual (5th ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-089592-nine. Contains a BNF grammar for C.
^ Kernighan & Ritchie (1996), p. 192.
^ Kernighan & Ritchie (1978), p. iii.
^ "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 Oct 21, 2008. Retrieved June 26, 2009.
^ Schultz, Thomas (2004). C and the 8051 (third ed.). Otsego, MI: PageFree Publishing Inc. p. 20. ISBN978-i-58961-237-ii. Archived from the original on July 29, 2020. Retrieved Feb x, 2012.
^ Kernighan & Ritchie (1978), p. six.
^ ^a ^b ^c ^d ^{due east} ^f ^g Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-one-4493-2714-9.
^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparison of the Programming Languages C and Pascal". ACM Calculating Surveys. 14 (1): 73–92. doi:10.1145/356869.356872. S2CID 3136859.
^ Kernighan & Ritchie (1996), p. 122.
^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on Jan 7, 2007. Retrieved August v, 2012.
^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-Teaching PUBLIC Company Limited. pp. 225–230. ISBN978-616-08-2740-4.
^ Raymond, Eric Southward. (October eleven, 1996). The New Hacker's Lexicon (third ed.). MIT Printing. p. 432. ISBN978-0-262-68092-9. Archived from the original on November 12, 2012. Retrieved August five, 2012.
^ "Man Page for lint (freebsd Section 1)". unix.com. May 24, 2001. Retrieved July 15, 2014.
^ Dale, Nell B.; Weems, Chip (2014). Programming and problem solving with C++ (sixth ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
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^ "Using C for CGI Programming". linuxjournal.com. March i, 2005. Archived from the original on February 13, 2010. Retrieved January 4, 2010.
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Sources

Ritchie, Dennis M. (March 1993). "The Evolution 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 2nd ACM SIGPLAN Conference on History of Programming Languages (HOPL-II). ACM. pp. 201–208. doi:10.1145/154766.155580. ISBN0-89791-570-4 . Retrieved Nov 4, 2014.
Kernighan, Brian W.; Ritchie, Dennis M. (1996). The C Programming Linguistic communication (2nd ed.). Prentice Hall. ISBNseven-302-02412-X.

External links

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

This folio was concluding edited on 1 March 2022, at 08:47

C# Reading a Text File Into Separate List

Source: https://wiki2.org/en/C_(programming_language)

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