Standardní knihovna jazyka C: Porovnání verzí
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'''Standardní knihovna jazyka C''' je v [[Informatika (počítačová věda)|informatice]] sada standardů pro [[Knihovna (programování)|knihovny]] a [[Hlavičkový soubor|hlavičkové soubory]] [[C (programovací jazyk)|programovacího jazyka C]] dle normy [[C (programovací jazyk)#ANSI C a ISO C|ISO C]]. Obsahuje funkce jazyka C zajištující [[Vstup/výstup|vstup a výstup]], práci s [[Textový řetězec|textovými řetězci]] a podobně. Standardní knihovna jazyka C je standardizováné rozhraní jazyka C popsané tímto dokumentem, nejedná se však o programovou knihovnu, jež by byla propojitelná s programy napsanými v jazyce C, knihovna s tímto názvem neexistuje.
Termín '''[[knihovna run-time]] jazyka C''' se na některých platformách používá pro označení sady základních knihoven, které mají za úkol dynamické propojení s operačním systémem (za i bez podpory hlavičkových souborů).Tohoto označení se také užívá pro knihovny distribuované s kompilátorem jazyka C. Označení '''run-time''' se run time in this context means the run-time support package associated with a compiler which is understood to make a language complete. The run-time support provides not only the C standard library functions, but possibly other material needed create an environment for the C program, such as initialization prior to the invocation of the <code>main</code> function, or subroutines to provide arithmetic operations missing from the CPU that are needed by code generated by the C compiler.
== Historie ==
The [[C (programming language)|C programming language]], before it was standardized, did not provide built-in functionalities such as I/O operations (unlike traditional languages such as Cobol and [[Fortran]]). Over time, user communities of C shared ideas and implementations of what is now called '''C standard libraries''' to provide that functionality. Many of these ideas were incorporated eventually into the definition of the standardized C programming language.
Both [[Unix]] and [[C (programming language)|C]] were created at [[Bell Labs|AT&T's Bell Laboratories]] in the late 1960s and early 1970s. During the 1970s the C programming language became increasingly popular. Many universities and organizations began creating their own variations of the language for their own projects. By the beginning of the 1980s compatibility problems between the various C implementations became apparent. In 1983 the [[American National Standards Institute]] (ANSI) formed a committee to establish a standard specification of C known as "ANSI C". This work culminated in the creation of the so-called '''C89''' standard in 1989. Part of the resulting standard was a set of [[software libraries]] called the '''ANSI C standard library'''.
Later revisions of the C standard have added several new required header files to the library. Support for these new extensions varies between implementations.
The headers '''<iso646.h>''', '''<wchar.h>''', and '''<wctype.h>''' were added with [[Normative Addendum 1]] (hereafter abbreviated as '''NA1'''), an addition to the C Standard ratified in 1995.
The headers '''<complex.h>''', '''<fenv.h>''', '''<inttypes.h>''', '''<stdbool.h>''', '''<stdint.h>''', and '''<tgmath.h>''' were added with '''[[C (programming language)#C99|C99]]''', a revision to the C Standard published in 1999.
== Standard ISO ==
The ISO C standard library consists of 24 C header files which can be included into a programmer's project with a single directive. Each header file contains one or more function declarations, data type definitions and macros. The contents of these header files follows.
In comparison to some other languages (for example [[Java (programming language)|Java]]) the standard library is minuscule. The library provides a basic set of mathematical functions, string manipulation, type conversions, and file and console-based I/O. It does not include a standard set of "[[Container (data structure)|container types]]" like the [[C++]] [[Standard Template Library]], let alone the complete [[graphical user interface]] (GUI) toolkits, networking tools, and profusion of other functionality that Java provides as standard. The main advantage of the small standard library is that providing a working ISO C environment is much easier than it is with other languages, and consequently porting C to a new platform is relatively easy.
Many other libraries have been developed to supply equivalent functionality to that provided by other languages in their standard library. For instance, the [[GNOME]] desktop environment project has developed the [[GTK+]] graphics toolkit and [[GLib]], a library of container data structures, and there are many other well-known examples. The variety of libraries available has meant that some superior toolkits have proven themselves through history. The considerable downside is that they often do not work particularly well together, programmers are often familiar with different sets of libraries, and a different set of them may be available on any particular platform.
=== ISO C hlaviček knihoven ===
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|''' [[assert.h|<assert.h>]]''' || Contains the [[assertion (computing)|assert]] macro, used to assist with detecting logical errors and other types of bug in debugging versions of a program.
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|''' [[complex.h|<complex.h>]]''' || A set of functions for manipulating [[complex number]]s. (New with '''C99''')
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|''' [[ctype.h|<ctype.h>]]''' || Contains functions used to classify characters by their types or to convert between upper and lower case in a way that is independent of the used [[character set]] (typically [[ASCII]] or one of its extensions, although implementations utilizing [[EBCDIC]] are also known).
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|''' [[errno.h|<errno.h>]]''' || For testing error codes reported by library functions.
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|''' [[fenv.h|<fenv.h>]]''' || For controlling [[floating-point]] environment. (New with '''C99''')
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|''' [[float.h|<float.h>]]''' || Contains defined constants specifying the implementation-specific properties of the [[floating-point]] library, such as the minimum difference between two different floating-point numbers (_EPSILON), the maximum number of digits of accuracy (_DIG) and the range of numbers which can be represented (_MIN, _MAX).
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|''' [[inttypes.h|<inttypes.h>]]''' || For precise conversion between integer types. (New with '''C99''')
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|''' [[iso646.h|<iso646.h>]]''' || For programming in [[ISO 646]] variant character sets. (New with '''NA1''')
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|''' [[limits.h|<limits.h>]]''' || Contains defined constants specifying the implementation-specific properties of the integer types, such as the range of numbers which can be represented (_MIN, _MAX).
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|''' [[locale.h|<locale.h>]]''' || For setlocale() and related constants. This is used to choose an appropriate [[Internationalization and localization|locale]].
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|''' [[math.h|<math.h>]]''' || For computing common mathematical functions
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|''' [[setjmp.h|<setjmp.h>]]''' || Declares the macros setjmp and longjmp, which are used for non-local exits
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|''' [[signal.h|<signal.h>]]''' || For controlling various exceptional conditions
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|''' [[stdarg.h|<stdarg.h>]]''' || For accessing a varying number of arguments passed to functions.
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|''' [[stdbool.h|<stdbool.h>]]''' || For a boolean data type. (New with '''C99''')
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|''' [[stdint.h|<stdint.h>]] ''' || For defining various integer types. (New with '''C99''')
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|''' [[stddef.h|<stddef.h>]]''' || For defining several useful types and macros.
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|''' [[stdio.h|<stdio.h>]]''' || Provides the core input and output capabilities of the C language. This file includes the venerable <code>[[printf]]</code> function.
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|''' [[stdlib.h|<stdlib.h>]]''' || For performing a variety of operations, including conversion, [[Pseudorandom number generator|pseudo-random numbers]], memory allocation, process control, environment, signalling, searching, and sorting.
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|''' [[string.h|<string.h>]]''' || For manipulating several kinds of strings.
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|''' [[tgmath.h|<tgmath.h>]]''' || For type-generic mathematical functions. (New with '''C99''')
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|''' [[time.h|<time.h>]]''' || For converting between various time and date formats.
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|''' [[wchar.h|<wchar.h>]]''' || For manipulating wide streams and several kinds of strings using wide characters - key to supporting a range of languages. (New with '''NA1''')
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|''' [[wctype.h|<wctype.h>]]''' || For classifying wide characters. (New with '''NA1''')
|}
== Standardní knihovna jazyka C v jiných jazycích ==
Some languages include the functionality of the standard C library in their own libraries. The library may be adapted to better suit the language's structure, but the operation semantics are kept similar. The [[C++]] programming language, for example, includes the functionality of the ANSI C standard library in the [[namespace (programming)|namespace]] '''std''' (like <code>std::printf</code>, <code>std::atoi</code>, <code>std::feof</code>, etc.), in header files with similar names to the C ones ("<code>cstdio</code>", "<code>cmath</code>", "<code>cstdlib</code>", etc). Other languages that take similar approaches are [[D (programming language)|D]] and the predominant implementation of [[Python (programming language)|Python]] known as [[CPython]]. In the latter, for example, the [[built-in]] '''file''' object is defined as ''"implemented using C's stdio package"[http://docs.python.org/lib/bltin-file-objects.html]'', so that the available operations (open, read, write, etc.) are expected to have the same behavior as the corresponding C functions.
== Funkce compileru ==
Some compilers (for example, [[GNU Compiler Collection|GCC]]<ref>[http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Other-Builtins.html#Other-Builtins Other built-in functions provided by GCC], GCC Manual</ref>) provide built-in versions of many of the functions in the C standard library; that is, the implementations of the functions are written into the compiled [[object file]], and the program calls the built-in versions instead of the functions in the C library [[shared object]] file. This reduces function call overhead, especially if function calls are replaced with [[inline function|inline]] variants, and allows other forms of [[Compiler optimization|optimisation]] (as the compiler knows the [[Control flow|control-flow]] characteristics of the built-in variants), but may cause confusion when debugging (for example, the built-in versions cannot be replaced with [[Instrumentation (computer programming)|instrumented]] variants).
However, the built-in functions must behave like ordinary functions in accordance with ISO C. The main implication is that the program must be able to create a pointer to these functions by taking their address, and invoke the function by means of that pointer. If two pointers to the same function are derived in two different translation unit in the program, these two pointers must compare equal; that is, the address comes by resolving the name of the function, which has external (program-wide) linkage.
== Standardní knihovna POSIX ==
{{main|C POSIX library}}
[[POSIX]] (and [[Single Unix Specification|SUS]]) specifies a number of routines that should be available over and above those in the C standard library proper; these are often implemented alongside the C standard library functionality, with varying degrees of closeness. For example, [[glibc]] implements functions such as [[Fork (operating system)|fork]] within libc.so, but before [[NPTL]] was merged into glibc it constituted a separate library with its own linker flag. Often, this POSIX-specified functionality will be regarded as part of the library; the C library proper may be identified as the ANSI or [[International Organization for Standardization| ISO]] C library.
== Implementace ==
Unix-like systems typically have a C library in [[shared library]] form, but the header files (and compiler toolchain) may be absent from an installation so C development may not be possible. The C library is considered part of the operating system on Unix-like systems. The C functions, including the ISO C standard ones, are widely used by programs, and are regarded as if they were not only an implementation of something in the C language, but also de facto part of the operating system interface. Unix-like operating systems generally cannot function if the C library is erased.
By contrast, on Microsoft Windows, the core system dynamic libraries ([[DLL]]s) do not provide an implementation of the C standard library; this is provided by each compiler individually. Compiled applications written in C are either statically linked with a C library, or linked to a dynamic version of the library that is shipped with these applications, rather than relied upon to be present on the targeted systems. Functions in a compiler's C library are not regarded as interfaces to Microsoft Windows.
Many other implementations exist, provided with both various operating systems and C compilers.
Seznam nejznámějších implementací:
* [[BSD libc]] – implementace pro operační systémy [[Berkeley Software Distribution|BSD]]
* [[GNU C Library]] – nejběžnější implementace používaná [[UN*X|unixovými]] systémy, jako je například [[Linux]]
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| článek = C standard library
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