C语言中的库函数定义在什么地方啊?

先顶一下楼上的，厉害~~~~~~~~~~
这对代码没有一个有用的。其实在头文件中只有函数的声明而没有函数的定义。这个头文件是给程序员看的，好让你知道有这些函数。那真正的函数定义在那呢？其实库文件中的函数早就已经编译好了存在.obj或者是.lib的文件里面。这种是静态的连接模式。在你的程序便已完成以后连接器再将你的程序的.obj文件和库文件进行连接最后生成.exe文件。如果你想看库文件的定义的话只能去网上自己找找啦。不过我个人感觉没有这个必要。其实大部分的库文件都是能够自己编写的。像strcmp()这种微软的库文件是更不可能放出原码的，不过可以去msdn里面碰碰运气。最后祝你好运啦。

D:\Microsoft Visual C++ 6\VC98\INCLUDE\string.h

/***
*string.h - declarations for string manipulation functions
*
* Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* This file contains the function declarations for the string
* manipulation functions.
* [ANSI/System V]
*
* [Public]
*
****/

#if _MSC_VER > 1000
#pragma once
#endif

#ifndef _INC_STRING
#define _INC_STRING

#if !defined(_WIN32) && !defined(_MAC)
#error ERROR: Only Mac or Win32 targets supported!
#endif

#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 _MAC
#ifndef _WCHAR_T_DEFINED
typedef unsigned short wchar_t;
#define _WCHAR_T_DEFINED
#endif
#endif /* ndef _MAC */

#ifndef _NLSCMP_DEFINED
#define _NLSCMPERROR 2147483647 /* currently == INT_MAX */
#define _NLSCMP_DEFINED
#endif

/* Define NULL pointer value */

#ifndef NULL
#ifdef __cplusplus
#define NULL 0
#else
#define NULL ((void *)0)
#endif
#endif

/* Function prototypes */

#ifdef _M_MRX000
_CRTIMP void * __cdecl memcpy(void *, const void *, size_t);
_CRTIMP int __cdecl memcmp(const void *, const void *, size_t);
_CRTIMP void * __cdecl memset(void *, int, size_t);
_CRTIMP char * __cdecl _strset(char *, int);
_CRTIMP char * __cdecl strcpy(char *, const char *);
_CRTIMP char * __cdecl strcat(char *, const char *);
_CRTIMP int __cdecl strcmp(const char *, const char *);
_CRTIMP size_t __cdecl strlen(const char *);
#else
void * __cdecl memcpy(void *, const void *, size_t);
int __cdecl memcmp(const void *, const void *, size_t);
void * __cdecl memset(void *, int, size_t);
char * __cdecl _strset(char *, int);
char * __cdecl strcpy(char *, const char *);
char * __cdecl strcat(char *, const char *);
int __cdecl strcmp(const char *, const char *);
size_t __cdecl strlen(const char *);
#endif
_CRTIMP void * __cdecl _memccpy(void *, const void *, int, unsigned int);
_CRTIMP void * __cdecl memchr(const void *, int, size_t);
_CRTIMP int __cdecl _memicmp(const void *, const void *, unsigned int);

#ifdef _M_ALPHA
/* memmove is available as an intrinsic in the Alpha compiler */
void * __cdecl memmove(void *, const void *, size_t);
#else
_CRTIMP void * __cdecl memmove(void *, const void *, size_t);
#endif

_CRTIMP char * __cdecl strchr(const char *, int);
_CRTIMP int __cdecl _strcmpi(const char *, const char *);
_CRTIMP int __cdecl _stricmp(const char *, const char *);
_CRTIMP int __cdecl strcoll(const char *, const char *);
_CRTIMP int __cdecl _stricoll(const char *, const char *);
_CRTIMP int __cdecl _strncoll(const char *, const char *, size_t);
_CRTIMP int __cdecl _strnicoll(const char *, const char *, size_t);
_CRTIMP size_t __cdecl strcspn(const char *, const char *);
_CRTIMP char * __cdecl _strdup(const char *);
_CRTIMP char * __cdecl _strerror(const char *);
_CRTIMP char * __cdecl strerror(int);
_CRTIMP char * __cdecl _strlwr(char *);
_CRTIMP char * __cdecl strncat(char *, const char *, size_t);
_CRTIMP int __cdecl strncmp(const char *, const char *, size_t);
_CRTIMP int __cdecl _strnicmp(const char *, const char *, size_t);
_CRTIMP char * __cdecl strncpy(char *, const char *, size_t);
_CRTIMP char * __cdecl _strnset(char *, int, size_t);
_CRTIMP char * __cdecl strpbrk(const char *, const char *);
_CRTIMP char * __cdecl strrchr(const char *, int);
_CRTIMP char * __cdecl _strrev(char *);
_CRTIMP size_t __cdecl strspn(const char *, const char *);
_CRTIMP char * __cdecl strstr(const char *, const char *);
_CRTIMP char * __cdecl strtok(char *, const char *);
_CRTIMP char * __cdecl _strupr(char *);
_CRTIMP size_t __cdecl strxfrm (char *, const char *, size_t);

#ifdef _MAC
unsigned char * __cdecl _c2pstr(char *);
char * __cdecl _p2cstr(unsigned char *);

#if !__STDC__
__inline unsigned char * __cdecl c2pstr(char *sz) { return _c2pstr(sz);};
__inline char * __cdecl p2cstr(unsigned char *sz) { return _p2cstr(sz);};
#endif
#endif

#if !__STDC__

/* prototypes for oldnames.lib functions */
_CRTIMP void * __cdecl memccpy(void *, const void *, int, unsigned int);
_CRTIMP int __cdecl memicmp(const void *, const void *, unsigned int);
_CRTIMP int __cdecl strcmpi(const char *, const char *);
_CRTIMP int __cdecl stricmp(const char *, const char *);
_CRTIMP char * __cdecl strdup(const char *);
_CRTIMP char * __cdecl strlwr(char *);
_CRTIMP int __cdecl strnicmp(const char *, const char *, size_t);
_CRTIMP char * __cdecl strnset(char *, int, size_t);
_CRTIMP char * __cdecl strrev(char *);
char * __cdecl strset(char *, int);
_CRTIMP char * __cdecl strupr(char *);

#endif /* !__STDC__ */

#ifndef _MAC
#ifndef _WSTRING_DEFINED

/* wide function prototypes, also declared in wchar.h */

_CRTIMP wchar_t * __cdecl wcscat(wchar_t *, const wchar_t *);
_CRTIMP wchar_t * __cdecl wcschr(const wchar_t *, wchar_t);
_CRTIMP int __cdecl wcscmp(const wchar_t *, const wchar_t *);
_CRTIMP wchar_t * __cdecl wcscpy(wchar_t *, const wchar_t *);
_CRTIMP size_t __cdecl wcscspn(const wchar_t *, const wchar_t *);
_CRTIMP size_t __cdecl wcslen(const wchar_t *);
_CRTIMP wchar_t * __cdecl wcsncat(wchar_t *, const wchar_t *, size_t);
_CRTIMP int __cdecl wcsncmp(const wchar_t *, const wchar_t *, size_t);
_CRTIMP wchar_t * __cdecl wcsncpy(wchar_t *, const wchar_t *, size_t);
_CRTIMP wchar_t * __cdecl wcspbrk(const wchar_t *, const wchar_t *);
_CRTIMP wchar_t * __cdecl wcsrchr(const wchar_t *, wchar_t);
_CRTIMP size_t __cdecl wcsspn(const wchar_t *, const wchar_t *);
_CRTIMP wchar_t * __cdecl wcsstr(const wchar_t *, const wchar_t *);
_CRTIMP wchar_t * __cdecl wcstok(wchar_t *, const wchar_t *);

_CRTIMP wchar_t * __cdecl _wcsdup(const wchar_t *);
_CRTIMP int __cdecl _wcsicmp(const wchar_t *, const wchar_t *);
_CRTIMP int __cdecl _wcsnicmp(const wchar_t *, const wchar_t *, size_t);
_CRTIMP wchar_t * __cdecl _wcsnset(wchar_t *, wchar_t, size_t);
_CRTIMP wchar_t * __cdecl _wcsrev(wchar_t *);
_CRTIMP wchar_t * __cdecl _wcsset(wchar_t *, wchar_t);

_CRTIMP wchar_t * __cdecl _wcslwr(wchar_t *);
_CRTIMP wchar_t * __cdecl _wcsupr(wchar_t *);
_CRTIMP size_t __cdecl wcsxfrm(wchar_t *, const wchar_t *, size_t);
_CRTIMP int __cdecl wcscoll(const wchar_t *, const wchar_t *);
_CRTIMP int __cdecl _wcsicoll(const wchar_t *, const wchar_t *);
_CRTIMP int __cdecl _wcsncoll(const wchar_t *, const wchar_t *, size_t);
_CRTIMP int __cdecl _wcsnicoll(const wchar_t *, const wchar_t *, size_t);

#if !__STDC__

/* old names */
#define wcswcs wcsstr

/* prototypes for oldnames.lib functions */
_CRTIMP wchar_t * __cdecl wcsdup(const wchar_t *);
_CRTIMP int __cdecl wcsicmp(const wchar_t *, const wchar_t *);
_CRTIMP int __cdecl wcsnicmp(const wchar_t *, const wchar_t *, size_t);
_CRTIMP wchar_t * __cdecl wcsnset(wchar_t *, wchar_t, size_t);
_CRTIMP wchar_t * __cdecl wcsrev(wchar_t *);
_CRTIMP wchar_t * __cdecl wcsset(wchar_t *, wchar_t);
_CRTIMP wchar_t * __cdecl wcslwr(wchar_t *);
_CRTIMP wchar_t * __cdecl wcsupr(wchar_t *);
_CRTIMP int __cdecl wcsicoll(const wchar_t *, const wchar_t *);

#endif /* !__STDC__ */

#define _WSTRING_DEFINED
#endif

#endif /* ndef _MAC */

#ifdef __cplusplus
}
#endif

#endif /* _INC_STRING */

你找lib这个目录,当然lib这个目录在很多的目录下都有.就象windows里的program
files这个目录在c盘下有,在d盘下也可以存在.不过red
hat在你装完系统后就会在几个地方创建了lib这个目录,这个目录下面的都是库文件.lib是libraray的简写,翻译成"库",说白了就是图书馆贝!注意登陆lib这个目录时,你可能只能用超级用户才能登陆上去,然后才能看.超级用户帐号默认是:root;注意用户名和密码都是这个

strcmp()函数具体是怎么实现的??
我可以告诉你，这个具体实现的代码，你是看不到的，因为MS已经把它做成lib了，至于你要看头文件，上面的这位已经都贴出来了。