标题：stdlib.h
简介
stdlib 头文件即standard library标准库头文件
stdlib 头文件里包含了C、C++语言的最常用的系统函数 
该文件包含了的C语言标准库函数的定义
stdlib.h里面定义了五种类型、一些宏和通用工具函数。 类型例如size_t、wchar_t、div_t、ldiv_t和lldiv_t； 宏例如EXIT_FAILURE、EXIT_SUCCESS、RAND_MAX和MB_CUR_MAX等等； 常用的函数如malloc()、calloc()、realloc()、free()、system()、atoi()、atol()、rand()、srand()、exit()等等。 具体的内容你自己可以打开编译器的include目录里面的stdlib.h头文件看看。
stdlib.h内容
/***
*stdlib.h - declarations/definitions for commonly used library functions
*
* Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* This include file contains the function declarations for commonly
* used library functions which either don't fit somewhere else, or,
* cannot be declared in the normal place for other reasons.
* [ANSI]
*
* [Public]
*
****/
#if _MSC_VER > 1000
#pragma once
#endif
#ifndef _INC_STDLIB
#define _INC_STDLIB
#if !defined(_WIN32) && !defined(_MAC)
#error ERROR: Only Mac or Win32 targets supported!
#endif
#ifdef _MSC_VER
/*
* Currently, all MS C compilers for Win32 platforms default to 8 byte
* alignment.
*/
#pragma pack(push,8)
#endif /* _MSC_VER */
#ifdef __cplusplus
extern "C" {
#endif
/* Define _CRTIMP */
#ifndef _CRTIMP
#ifdef _DLL
#define _CRTIMP __declspec(dllimport)
#else /* ndef _DLL */
#define _CRTIMP
#endif /* _DLL */
#endif /* _CRTIMP */
/* Define __cdecl for non-Microsoft compilers */
#if ( !defined(_MSC_VER) && !defined(__cdecl) )
#define __cdecl
#endif
/* Define _CRTAPI1 (for compatibility with the NT SDK) */
#ifndef _CRTAPI1
#if _MSC_VER >= 800 && _M_IX86 >= 300
#define _CRTAPI1 __cdecl
#else
#define _CRTAPI1
#endif
#endif
#ifndef _SIZE_T_DEFINED
typedef unsigned int size_t;
#define _SIZE_T_DEFINED
#endif
#ifndef _WCHAR_T_DEFINED
typedef unsigned short wchar_t;
#define _WCHAR_T_DEFINED
#endif
/* Define NULL pointer value */
#ifndef NULL
#ifdef __cplusplus
#define NULL 0
#else
#define NULL ((void *)0)
#endif
#endif
/* Definition of the argument values for the exit() function */
#define EXIT_SUCCESS 0
#define EXIT_FAILURE 1
#ifndef _ONEXIT_T_DEFINED
typedef int (__cdecl * _onexit_t)(void);
#if !__STDC__
/* Non-ANSI name for compatibility */
#define onexit_t _onexit_t
#endif
#define _ONEXIT_T_DEFINED
#endif
/* Data structure definitions for div and ldiv runtimes. */
#ifndef _DIV_T_DEFINED
typedef struct _div_t {
int quot;
int rem;
} div_t;
typedef struct _ldiv_t {
long quot;
long rem;
} ldiv_t;
#define _DIV_T_DEFINED
#endif
/* Maximum value that can be returned by the rand function. */
#define RAND_MAX 0x7fff
/*
* Maximum number of bytes in multi-byte character in the current locale
* (also defined in ctype.h).
*/
#ifndef MB_CUR_MAX
#define MB_CUR_MAX __mb_cur_max
_CRTIMP extern int __mb_cur_max;
#endif /* MB_CUR_MAX */
/* Minimum and maximum macros */
#define __max(a,b) (((a) > (b)) ? (a) : (b))
#define __min(a,b) (((a) < (b)) ? (a) : (b))
/*
* Sizes for buffers used by the _makepath() and _splitpath() functions.
* note that the sizes include space for 0-terminator
*/
#ifndef _MAC
#define _MAX_PATH 260 /* max. length of full pathname */
#define _MAX_DRIVE 3 /* max. length of drive component */
#define _MAX_DIR 256 /* max. length of path component */
#define _MAX_FNAME 256 /* max. length of file name component */
#define _MAX_EXT 256 /* max. length of extension component */
#else /* def _MAC */
#define _MAX_PATH 256 /* max. length of full pathname */
#define _MAX_DIR 32 /* max. length of path component */
#define _MAX_FNAME 64 /* max. length of file name component */
#endif /* _MAC */
/*
* Argument values for _set_error_mode().
*/
#define _OUT_TO_DEFAULT 0
#define _OUT_TO_STDERR 1
#define _OUT_TO_MSGBOX 2
#define _REPORT_ERRMODE 3
/* External variable declarations */
#if (defined(_MT) || defined(_DLL)) && !defined(_MAC)
_CRTIMP int * __cdecl _errno(void);
_CRTIMP unsigned long * __cdecl __doserrno(void);
#define errno (*_errno())
#define _doserrno (*__doserrno())
#else /* ndef _MT && ndef _DLL */
_CRTIMP extern int errno; /* XENIX style error number */
_CRTIMP extern unsigned long _doserrno; /* OS system error value */
#endif /* _MT || _DLL */
#ifdef _MAC
_CRTIMP extern int _macerrno; /* OS system error value */
#endif
_CRTIMP extern char * _sys_errlist[]; /* perror error message table */
_CRTIMP extern int _sys_nerr; /* # of entries in sys_errlist table */
#if defined(_DLL) && defined(_M_IX86)
#define __argc (*__p___argc()) /* count of cmd line args */
#define __argv (*__p___argv()) /* pointer to table of cmd line args */
#define __wargv (*__p___wargv()) /* pointer to table of wide cmd line args */
#define _environ (*__p__environ()) /* pointer to environment table */
#ifdef _POSIX_
extern char ** environ; /* pointer to environment table */
#else
#ifndef _MAC
#define _wenviron (*__p__wenviron()) /* pointer to wide environment table */
#endif /* ndef _MAC */
#endif /* _POSIX_ */
#define _pgmptr (*__p__pgmptr()) /* points to the module (EXE) name */
#ifndef _MAC
#define _wpgmptr (*__p__wpgmptr()) /* points to the module (EXE) wide name */
#endif /* ndef _MAC */
_CRTIMP int * __cdecl __p___argc(void);
_CRTIMP char *** __cdecl __p___argv(void);
_CRTIMP wchar_t *** __cdecl __p___wargv(void);
_CRTIMP char *** __cdecl __p__environ(void);
_CRTIMP wchar_t *** __cdecl __p__wenviron(void);
_CRTIMP char ** __cdecl __p__pgmptr(void);
_CRTIMP wchar_t ** __cdecl __p__wpgmptr(void);
#else
_CRTIMP extern int __argc; /* count of cmd line args */
_CRTIMP extern char ** __argv; /* pointer to table of cmd line args */
#ifndef _MAC
_CRTIMP extern wchar_t ** __wargv; /* pointer to table of wide cmd line args */
#endif /* ndef _MAC */
#ifdef _POSIX_
extern char ** environ; /* pointer to environment table */
#else
_CRTIMP extern char ** _environ; /* pointer to environment table */
#ifndef _MAC
_CRTIMP extern wchar_t ** _wenviron; /* pointer to wide environment table */
#endif /* ndef _MAC */
#endif /* _POSIX_ */
_CRTIMP extern char * _pgmptr; /* points to the module (EXE) name */
#ifndef _MAC
_CRTIMP extern wchar_t * _wpgmptr; /* points to the module (EXE) wide name */
#endif /* ndef _MAC */
#endif
_CRTIMP extern int _fmode; /* default file translation mode */
_CRTIMP extern int _fileinfo; /* open file info mode (for spawn) */
/* Windows major/minor and O.S. version numbers */
_CRTIMP extern unsigned int _osver;
_CRTIMP extern unsigned int _winver;
_CRTIMP extern unsigned int _winmajor;
_CRTIMP extern unsigned int _winminor;
/* function prototypes */
#if _MSC_VER >= 1200
_CRTIMP __declspec(noreturn) void __cdecl abort(void);
_CRTIMP __declspec(noreturn) void __cdecl exit(int);
#else
_CRTIMP void __cdecl abort(void);
_CRTIMP void __cdecl exit(int);
#endif
#if defined(_M_MRX000)
_CRTIMP int __cdecl abs(int);
#else
int __cdecl abs(int);
#endif
int __cdecl atexit(void (__cdecl *)(void));
_CRTIMP double __cdecl atof(const char *);
_CRTIMP int __cdecl atoi(const char *);
_CRTIMP long __cdecl atol(const char *);
#ifdef _M_M68K
_CRTIMP long double __cdecl _atold(const char *);
#endif
_CRTIMP void * __cdecl bsearch(const void *, const void *, size_t, size_t,
int (__cdecl *)(const void *, const void *));
_CRTIMP void * __cdecl calloc(size_t, size_t);
_CRTIMP div_t __cdecl div(int, int);
_CRTIMP void __cdecl free(void *);
_CRTIMP char * __cdecl getenv(const char *);
_CRTIMP char * __cdecl _itoa(int, char *, int);
#if _INTEGRAL_MAX_BITS >= 64
_CRTIMP char * __cdecl _i64toa(__int64, char *, int);
_CRTIMP char * __cdecl _ui64toa(unsigned __int64, char *, int);
_CRTIMP __int64 __cdecl _atoi64(const char *);
#endif
#if defined(_M_MRX000)
_CRTIMP long __cdecl labs(long);
#else
long __cdecl labs(long);
#endif
_CRTIMP ldiv_t __cdecl ldiv(long, long);
_CRTIMP char * __cdecl _ltoa(long, char *, int);
_CRTIMP void * __cdecl malloc(size_t);
_CRTIMP int __cdecl mblen(const char *, size_t);
_CRTIMP size_t __cdecl _mbstrlen(const char *s);
_CRTIMP int __cdecl mbtowc(wchar_t *, const char *, size_t);
_CRTIMP size_t __cdecl mbstowcs(wchar_t *, const char *, size_t);
_CRTIMP void __cdecl qsort(void *, size_t, size_t, int (__cdecl *)
(const void *, const void *));
_CRTIMP int __cdecl rand(void);
_CRTIMP void * __cdecl realloc(void *, size_t);
_CRTIMP int __cdecl _set_error_mode(int);
_CRTIMP void __cdecl srand(unsigned int);
_CRTIMP double __cdecl strtod(const char *, char **);
_CRTIMP long __cdecl strtol(const char *, char **, int);
#ifdef _M_M68K
_CRTIMP long double __cdecl _strtold(const char *, char **);
#endif
_CRTIMP unsigned long __cdecl strtoul(const char *, char **, int);
#ifndef _MAC
_CRTIMP int __cdecl system(const char *);
#endif
_CRTIMP char * __cdecl _ultoa(unsigned long, char *, int);
_CRTIMP int __cdecl wctomb(char *, wchar_t);
_CRTIMP size_t __cdecl wcstombs(char *, const wchar_t *, size_t);
#ifndef _MAC
#ifndef _WSTDLIB_DEFINED
/* wide function prototypes, also declared in wchar.h */
_CRTIMP wchar_t * __cdecl _itow (int, wchar_t *, int);
_CRTIMP wchar_t * __cdecl _ltow (long, wchar_t *, int);
_CRTIMP wchar_t * __cdecl _ultow (unsigned long, wchar_t *, int);
_CRTIMP double __cdecl wcstod(const wchar_t *, wchar_t **);
_CRTIMP long __cdecl wcstol(const wchar_t *, wchar_t **, int);
_CRTIMP unsigned long __cdecl wcstoul(const wchar_t *, wchar_t **, int);
_CRTIMP wchar_t * __cdecl _wgetenv(const wchar_t *);
_CRTIMP int __cdecl _wsystem(const wchar_t *);
_CRTIMP int __cdecl _wtoi(const wchar_t *);
_CRTIMP long __cdecl _wtol(const wchar_t *);
#if _INTEGRAL_MAX_BITS >= 64
_CRTIMP wchar_t * __cdecl _i64tow(__int64, wchar_t *, int);
_CRTIMP wchar_t * __cdecl _ui64tow(unsigned __int64, wchar_t *, int);
_CRTIMP __int64 __cdecl _wtoi64(const wchar_t *);
#endif
#define _WSTDLIB_DEFINED
#endif
#endif /* ndef _MAC */
#ifndef _POSIX_
_CRTIMP char * __cdecl _ecvt(double, int, int *, int *);
#if _MSC_VER >= 1200
_CRTIMP __declspec(noreturn) void __cdecl _exit(int);
#else
_CRTIMP void __cdecl _exit(int);
#endif
_CRTIMP char * __cdecl _fcvt(double, int, int *, int *);
_CRTIMP char * __cdecl _fullpath(char *, const char *, size_t);
_CRTIMP char * __cdecl _gcvt(double, int, char *);
unsigned long __cdecl _lrotl(unsigned long, int);
unsigned long __cdecl _lrotr(unsigned long, int);
#ifndef _MAC
_CRTIMP void __cdecl _makepath(char *, const char *, const char *, const char *,
const char *);
#endif
_onexit_t __cdecl _onexit(_onexit_t);
_CRTIMP void __cdecl perror(const char *);
_CRTIMP int __cdecl _putenv(const char *);
unsigned int __cdecl _rotl(unsigned int, int);
unsigned int __cdecl _rotr(unsigned int, int);
_CRTIMP void __cdecl _searchenv(const char *, const char *, char *);
#ifndef _MAC
_CRTIMP void __cdecl _splitpath(const char *, char *, char *, char *, char *);
#endif
_CRTIMP void __cdecl _swab(char *, char *, int);
#ifndef _MAC
#ifndef _WSTDLIBP_DEFINED
/* wide function prototypes, also declared in wchar.h */
_CRTIMP wchar_t * __cdecl _wfullpath(wchar_t *, const wchar_t *, size_t);
_CRTIMP void __cdecl _wmakepath(wchar_t *, const wchar_t *, const wchar_t *, const wchar_t *,
const wchar_t *);
_CRTIMP void __cdecl _wperror(const wchar_t *);
_CRTIMP int __cdecl _wputenv(const wchar_t *);
_CRTIMP void __cdecl _wsearchenv(const wchar_t *, const wchar_t *, wchar_t *);
_CRTIMP void __cdecl _wsplitpath(const wchar_t *, wchar_t *, wchar_t *, wchar_t *, wchar_t *);
#define _WSTDLIBP_DEFINED
#endif
#endif /* ndef _MAC */
/* --------- The following functions are OBSOLETE --------- */
/* The Win32 API SetErrorMode, Beep and Sleep should be used instead. */
#ifndef _MAC
_CRTIMP void __cdecl _seterrormode(int);
_CRTIMP void __cdecl _beep(unsigned, unsigned);
_CRTIMP void __cdecl _sleep(unsigned long);
#endif /* ndef _MAC */
/* --------- The preceding functions are OBSOLETE --------- */
#endif /* _POSIX_ */
#if !__STDC__
/* --------- The declarations below should not be in stdlib.h --------- */
/* --------- and will be removed in a future release. Include --------- */
/* --------- ctype.h to obtain these declarations. --------- */
#ifndef tolower /* tolower has been undefined - use function */
_CRTIMP int __cdecl tolower(int);
#endif /* tolower */
#ifndef toupper /* toupper has been undefined - use function */
_CRTIMP int __cdecl toupper(int);
#endif /* toupper */
/* --------- The declarations above will be removed. --------- */
#endif
#if !__STDC__
#ifndef _POSIX_
/* Non-ANSI names for compatibility */
#ifndef __cplusplus
#define max(a,b) (((a) > (b)) ? (a) : (b))
#define min(a,b) (((a) < (b)) ? (a) : (b))
#endif
#define sys_errlist _sys_errlist
#define sys_nerr _sys_nerr
#define environ _environ
_CRTIMP char * __cdecl ecvt(double, int, int *, int *);
_CRTIMP char * __cdecl fcvt(double, int, int *, int *);
_CRTIMP char * __cdecl gcvt(double, int, char *);
_CRTIMP char * __cdecl itoa(int, char *, int);
_CRTIMP char * __cdecl ltoa(long, char *, int);
onexit_t __cdecl onexit(onexit_t);
_CRTIMP int __cdecl putenv(const char *);
_CRTIMP void __cdecl swab(char *, char *, int);
_CRTIMP char * __cdecl ultoa(unsigned long, char *, int);
#endif /* _POSIX_ */
#endif /* __STDC__ */
#ifdef __cplusplus
}
#endif
#ifdef _MSC_VER
#pragma pack(pop)
#endif /* _MSC_VER */
#endif /* _INC_STDLIB */
stdlib.h包含函数
输入样式：C语言模式：#include <stdlib.h> 
C++样式：#include <cstdlib> 
1函数名称: calloc