C – string.h library functions

      All C inbuilt functions which are declared in string.h header file are given below. The source code for string.h header file is also given below for your reference.

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List of inbuilt C functions in string.h file:

S.no
string functions
Description
1 strcat(str1, str2)  Concatenates str2 at the end of str1.
2 strcpy(str1, str2)  Copies str2 into str1
3 strlen(strl)  gives the length of str1.
4 strcmp(str1, str2)  Returns 0 if str1 is same as str2. Returns <0 if strl < str2. Returns >0 if str1 > str2.
5 strchr(str1,char)  Returns pointer to first occurrence of char in str1.
6 strstr(str1, str2)  Returns pointer to first occurrence of str2 in str1.
7 strcmpi(str1,str2)  Same as strcmp() function. But, this function negotiates case.  “A” and “a” are treated as same.
8 strdup()  duplicates the string
9 strlwr()  converts string to lowercase
10 strncat()  appends a portion of string to another
11 strncpy()  copies given number of characters of one string to another
12 strrchr()  last occurrence of given character in a string is found
13 strrev()  reverses the given string
14 strset()  sets all character in a string to given character
15 strupr()  converts string to uppercase
16 strtok()  tokenizing given string using delimiter
17 memset() It is used to initialize a specified number of bytes to null or any other value in the buffer
18 memcpy() It is used to copy a specified number of bytes from one memory to another
19 memmove() It is used to copy a specified number of bytes from one memory to another or to overlap on same memory.
20 memcmp() It is used to compare specified number of characters from two buffers
21 memicmp() It is used to compare specified number of characters from two buffers  regardless of the case of the characters
22 memchr() It is used to locate the first occurrence of the character in the specified string

Source code for string.h header file:

    Please find the source code for string.h header file below. This code is taken from DevC++ compiler files for your reference.

/*
 * string.h
 * This file has no copyright assigned and is placed in the Public Domain.
 * This file is a part of the mingw-runtime package.
 * No warranty is given; refer to the file DISCLAIMER within the package.
 *
 * Definitions for memory and string functions.
 *
 */

#ifndef _STRING_H_
#define	_STRING_H_

/* All the headers include this file. */
#include <_mingw.h>

/*
 * Define size_t, wchar_t and NULL
 */
#define __need_size_t
#define __need_wchar_t
#define	__need_NULL
#ifndef RC_INVOKED
#include <stddef.h>
#endif	/* Not RC_INVOKED */

#ifndef RC_INVOKED

#ifdef __cplusplus
extern "C" {
#endif

/*
 * Prototypes of the ANSI Standard C library string functions.
 */
_CRTIMP void* __cdecl	memchr (const void*, int, size_t) __MINGW_ATTRIB_PURE;
_CRTIMP int __cdecl 	memcmp (const void*, const void*, size_t) __MINGW_ATTRIB_PURE;
_CRTIMP void* __cdecl 	memcpy (void*, const void*, size_t);
_CRTIMP void* __cdecl	memmove (void*, const void*, size_t);
_CRTIMP void* __cdecl	memset (void*, int, size_t);
_CRTIMP char* __cdecl	strcat (char*, const char*);
_CRTIMP char* __cdecl	strchr (const char*, int)  __MINGW_ATTRIB_PURE;
_CRTIMP int __cdecl	strcmp (const char*, const char*)  __MINGW_ATTRIB_PURE;
_CRTIMP int __cdecl	strcoll (const char*, const char*);	/* Compare using locale */
_CRTIMP char* __cdecl	strcpy (char*, const char*);
_CRTIMP size_t __cdecl	strcspn (const char*, const char*)  __MINGW_ATTRIB_PURE;
_CRTIMP char* __cdecl	strerror (int); /* NOTE: NOT an old name wrapper. */

_CRTIMP size_t __cdecl	strlen (const char*)  __MINGW_ATTRIB_PURE;
_CRTIMP char* __cdecl	strncat (char*, const char*, size_t);
_CRTIMP int __cdecl	strncmp (const char*, const char*, size_t)  __MINGW_ATTRIB_PURE;
_CRTIMP char* __cdecl	strncpy (char*, const char*, size_t);
_CRTIMP char* __cdecl	strpbrk (const char*, const char*)  __MINGW_ATTRIB_PURE;
_CRTIMP char* __cdecl	strrchr (const char*, int)  __MINGW_ATTRIB_PURE;
_CRTIMP size_t __cdecl	strspn (const char*, const char*)  __MINGW_ATTRIB_PURE;
_CRTIMP char* __cdecl	strstr (const char*, const char*)  __MINGW_ATTRIB_PURE;
_CRTIMP char* __cdecl	strtok (char*, const char*);
_CRTIMP size_t __cdecl	strxfrm (char*, const char*, size_t);

#ifndef __STRICT_ANSI__
/*
 * Extra non-ANSI functions provided by the CRTDLL library
 */
_CRTIMP char* __cdecl	_strerror (const char *);
_CRTIMP void* __cdecl	_memccpy (void*, const void*, int, size_t);
_CRTIMP int __cdecl 	_memicmp (const void*, const void*, size_t);
_CRTIMP char* __cdecl 	_strdup (const char*) __MINGW_ATTRIB_MALLOC;
_CRTIMP int __cdecl	_strcmpi (const char*, const char*);
_CRTIMP int __cdecl	_stricmp (const char*, const char*);
_CRTIMP int __cdecl	_stricoll (const char*, 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*);
_CRTIMP char* __cdecl	_strset (char*, int);
_CRTIMP char* __cdecl	_strupr (char*);
_CRTIMP void __cdecl	_swab (const char*, char*, size_t);

#ifdef __MSVCRT__
_CRTIMP int __cdecl  _strncoll(const char*, const char*, size_t);
_CRTIMP int __cdecl  _strnicoll(const char*, const char*, size_t);
#endif

#ifndef	_NO_OLDNAMES
/*
 * Non-underscored versions of non-ANSI functions. They live in liboldnames.a
 * and provide a little extra portability. Also a few extra UNIX-isms like
 * strcasecmp.
 */
_CRTIMP void* __cdecl	memccpy (void*, const void*, int, size_t);
_CRTIMP int __cdecl	memicmp (const void*, const void*, size_t);
_CRTIMP char* __cdecl	strdup (const char*) __MINGW_ATTRIB_MALLOC;
_CRTIMP int __cdecl	strcmpi (const char*, const char*);
_CRTIMP int __cdecl	stricmp (const char*, const char*);
__CRT_INLINE int __cdecl
strcasecmp (const char * __sz1, const char * __sz2)
  {return _stricmp (__sz1, __sz2);}
_CRTIMP int __cdecl	stricoll (const char*, const char*);
_CRTIMP char* __cdecl	strlwr (char*);
_CRTIMP int __cdecl	strnicmp (const char*, const char*, size_t);
__CRT_INLINE int __cdecl
strncasecmp (const char * __sz1, const char * __sz2, size_t __sizeMaxCompare)
  {return _strnicmp (__sz1, __sz2, __sizeMaxCompare);}
_CRTIMP char* __cdecl	strnset (char*, int, size_t);
_CRTIMP char* __cdecl	strrev (char*);
_CRTIMP char* __cdecl	strset (char*, int);
_CRTIMP char* __cdecl	strupr (char*);
#ifndef _UWIN
_CRTIMP void __cdecl	swab (const char*, char*, size_t);
#endif /* _UWIN */
#endif /* _NO_OLDNAMES */

#endif	/* Not __STRICT_ANSI__ */

#ifndef _WSTRING_DEFINED
/*
 * Unicode versions of the standard calls.
 * Also in wchar.h, where they belong according to ISO standard.
 */
_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 int __cdecl	wcscoll (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*);
/* Note:  _wcserror requires __MSVCRT_VERSION__ >= 0x0700.  */
_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 size_t __cdecl	wcsxfrm(wchar_t*, const wchar_t*, size_t);

#ifndef	__STRICT_ANSI__
/*
 * Unicode versions of non-ANSI string functions provided by CRTDLL.
 */

/* NOTE: _wcscmpi not provided by CRTDLL, this define is for portability */
#define		_wcscmpi	_wcsicmp

_CRTIMP wchar_t* __cdecl _wcsdup (const wchar_t*);
_CRTIMP int __cdecl	_wcsicmp (const wchar_t*, const wchar_t*);
_CRTIMP int __cdecl	_wcsicoll (const wchar_t*, const wchar_t*);
_CRTIMP wchar_t* __cdecl _wcslwr (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 _wcsupr (wchar_t*);

#ifdef __MSVCRT__
_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 __MSVCRT_VERSION__ >= 0x0700
_CRTIMP  wchar_t* __cdecl _wcserror(int);
_CRTIMP  wchar_t* __cdecl __wcserror(const wchar_t*);
#endif
#endif

#ifndef	_NO_OLDNAMES
/* NOTE: There is no _wcscmpi, but this is for compatibility. */
int __cdecl wcscmpi (const wchar_t * __ws1, const wchar_t * __ws2);
__CRT_INLINE int __cdecl
wcscmpi (const wchar_t * __ws1, const wchar_t * __ws2)
  {return _wcsicmp (__ws1, __ws2);}
_CRTIMP wchar_t* __cdecl wcsdup (const wchar_t*);
_CRTIMP int __cdecl	wcsicmp (const wchar_t*, const wchar_t*);
_CRTIMP int __cdecl	wcsicoll (const wchar_t*, const wchar_t*);
_CRTIMP wchar_t* __cdecl wcslwr (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 wcsupr (wchar_t*);
#endif	/* Not _NO_OLDNAMES */

#endif	/* Not strict ANSI */

#define _WSTRING_DEFINED
#endif  /* _WSTRING_DEFINED */

#ifdef __cplusplus
}
#endif

#endif	/* Not RC_INVOKED */

#endif	/* Not _STRING_H_ */