/*file:string.h#ifndef _LINUX_STRING_H_#define _LINUX_STRING_H_/* We don't want strings.h stuff being user by user stuff by accident */#ifdef __KERNEL__#include <linux/types.h> /* for size_t */#include <linux/stddef.h> /* for NULL */#include <linux/compiler.h> /* for inline ((always_inline)) */#ifdef __cplusplusextern "C" {#endifextern char * ___strtok;extern char * strpbrk(const char *,const char *);extern char * strtok(char *,const char *);extern char * strsep(char **,const char *);extern __kernel_size_t strspn(const char *,const char *);/* * Include machine specific inline routines */#include <asm/string.h>#ifndef __HAVE_ARCH_STRCPYextern char * strcpy(char *,const char *);#endif#ifndef __HAVE_ARCH_STRNCPYextern char * strncpy(char *,const char *, __kernel_size_t);#endif#ifndef __HAVE_ARCH_STRCATextern char * strcat(char *, const char *);#endif#ifndef __HAVE_ARCH_STRNCATextern char * strncat(char *, const char *, __kernel_size_t);#endif#ifndef __HAVE_ARCH_STRCMPextern int strcmp(const char *,const char *);#endif#ifndef __HAVE_ARCH_STRNCMPextern int strncmp(const char *,const char *,__kernel_size_t);#endif#ifndef __HAVE_ARCH_STRNICMPextern int strnicmp(const char *, const char *, __kernel_size_t);#endif#ifndef __HAVE_ARCH_STRCHRextern char * strchr(const char *,int);#endif#ifndef __HAVE_ARCH_STRRCHRextern char * strrchr(const char *,int);#endif#ifndef __HAVE_ARCH_STRSTRextern char * strstr(const char *,const char *);#endif#ifndef __HAVE_ARCH_STRLENextern __kernel_size_t strlen(const char *);#endif#ifndef __HAVE_ARCH_STRNLENextern __kernel_size_t strnlen(const char *,__kernel_size_t);#endif#ifndef __HAVE_ARCH_MEMSETextern void * memset(void *,int,__kernel_size_t);#endif#ifndef __HAVE_ARCH_MEMCPYextern void * memcpy(void *,const void *,__kernel_size_t);#endif#ifndef __HAVE_ARCH_MEMMOVEextern void * memmove(void *,const void *,__kernel_size_t);#endif#ifndef __HAVE_ARCH_MEMSCANextern void * memscan(void *,int,__kernel_size_t);#endif#ifndef __HAVE_ARCH_MEMCMPextern int memcmp(const void *,const void *,__kernel_size_t);#endif#ifndef __HAVE_ARCH_MEMCHRextern void * memchr(const void *,int,__kernel_size_t);#endif#ifdef __cplusplus}#endif#endif#endif /* _LINUX_STRING_H_ */*/
实现文件string.c
/* * linux/lib/string.c * * Copyright (C) 1991, 1992 Linus Torvalds *//* * stupid library routines.. The optimized versions should generally be found * as inline code in <asm-xx/string.h> * * These are buggy as well.. * * * Fri Jun 25 1999, Ingo Oeser <ioe@informatik.tu-chemnitz.de> * - Added strsep() which will replace strtok() soon (because strsep() is * reentrant and should be faster). Use only strsep() in new code, please. */#include <linux/types.h>#include <linux/string.h>#include <linux/ctype.h>#ifndef __HAVE_ARCH_STRNICMP/** * strnicmp - Case insensitive(忽视大小写), length-limited string comparison * @s1: One string * @s2: The other string * @len: the maximum number of characters to compare */int strnicmp(const char *s1, const char *s2, size_t len){ /* Yes, Virginia, it had better be unsigned */ unsigned char c1, c2; c1 = 0; c2 = 0; if (len) { do { c1 = *s1; c2 = *s2; s1++; s2++; //是否已到字符串的末尾或两字符串是否有空串,如果到了末尾或有空串,则比较完毕 if (!c1) break; if (!c2) break; //如果没有,且字符串相等,则继续比较下个字符 if (c1 == c2) continue; //如果不相同,则同时转换为小写字符再进行比较 c1 = tolower(c1); c2 = tolower(c2); //如果不相同,则比较完毕,否则继续 if (c1 != c2) break; } while (--len); } return (int)c1 - (int)c2;}#endifchar * ___strtok;#ifndef __HAVE_ARCH_STRCPY/** * strcpy - Copy a %NUL terminated string * @dest: Where to copy the string to * @src: Where to copy the string from */char * strcpy(char * dest,const char *src){ char *tmp = dest; while ((*dest++ = *src++) != '\0') /* nothing */; return tmp;}#endif#ifndef __HAVE_ARCH_STRNCPY/** * strncpy - Copy a length-limited, %NUL-terminated string * @dest: Where to copy the string to * @src: Where to copy the string from * @count: The maximum number of bytes to copy * * Note that unlike userspace strncpy, this does not %NUL-pad the buffer. * However, the result is not %NUL-terminated if the source exceeds * @count bytes. */char * strncpy(char * dest,const char *src,size_t count){ char *tmp = dest; while (count-- && (*dest++ = *src++) != '\0') /* nothing */; return tmp;}#endif#ifndef __HAVE_ARCH_STRCAT/** * strcat - Append one %NUL-terminated string to another * @dest: The string to be appended to * @src: The string to append to it */char * strcat(char * dest, const char * src){ char *tmp = dest; while (*dest) dest++; while ((*dest++ = *src++) != '\0') ; return tmp;}#endif#ifndef __HAVE_ARCH_STRNCAT/** * strncat - Append a length-limited, %NUL-terminated string to another * @dest: The string to be appended to * @src: The string to append to it * @count: The maximum numbers of bytes to copy * * Note that in contrast to strncpy, strncat ensures the result is * terminated. */char * strncat(char *dest, const char *src, size_t count){ char *tmp = dest; if (count) { //如果追加的字符数不为0 while (*dest) //达到字符串的末尾 dest++; while ((*dest++ = *src++)) { //如果没有到源字符串末尾 if (--count == 0) { //如果已经追加了count字符 *dest = '\0';//末尾置null字符 break;//结束循环 } } } return tmp;}#endif#ifndef __HAVE_ARCH_STRCMP/** * strcmp - Compare two strings * @cs: One string * @ct: Another string */int strcmp(const char * cs,const char * ct){ register signed char __res; while (1) { if ((__res = *cs - *ct++) != 0 || !*cs++) break; } return __res;}#endif#ifndef __HAVE_ARCH_STRNCMP/** * strncmp - Compare two length-limited strings * @cs: One string * @ct: Another string * @count: The maximum number of bytes to compare */int strncmp(const char * cs,const char * ct,size_t count){ register signed char __res = 0; while (count) { if ((__res = *cs - *ct++) != 0 || !*cs++) break; count--; } return __res;}#endif#ifndef __HAVE_ARCH_STRCHR/** * strchr - Find the first occurrence of a character in a string * @s: The string to be searched * @c: The character to search for */char * strchr(const char * s, int c){ for(; *s != (char) c; ++s) if (*s == '\0') return NULL; return (char *) s;}#endif#ifndef __HAVE_ARCH_STRRCHR/** * strrchr - Find the last occurrence of a character in a string * @s: The string to be searched * @c: The character to search for */char * strrchr(const char * s, int c){ const char *p = s + strlen(s); do { if (*p == (char)c) return (char *)p; } while (--p >= s); return NULL;}#endif#ifndef __HAVE_ARCH_STRLEN/** * strlen - Find the length of a string * @s: The string to be sized */size_t strlen(const char * s){ const char *sc; for (sc = s; *sc != '\0'; ++sc) /* nothing */; return sc - s;}#endif#ifndef __HAVE_ARCH_STRNLEN/** * strnlen - Find the length of a length-limited string * @s: The string to be sized * @count: The maximum number of bytes to search */size_t strnlen(const char * s, size_t count){ const char *sc; for (sc = s; count-- && *sc != '\0'; ++sc) /* nothing */; return sc - s;}#endif#ifndef __HAVE_ARCH_STRSPN/** * strspn - Calculate the length of the initial substring of @s which only * contain letters in @accept * @s: The string to be searched * @accept: The string to search for */size_t strspn(const char *s, const char *accept){ const char *p; const char *a; size_t count = 0; for (p = s; *p != '\0'; ++p) { for (a = accept; *a != '\0'; ++a) { if (*p == *a) break; } if (*a == '\0') return count; ++count; } return count;}#endif#ifndef __HAVE_ARCH_STRPBRK/** * strpbrk - Find the first occurrence of a set of characters * @cs: The string to be searched * @ct: The characters to search for */char * strpbrk(const char * cs,const char * ct){ const char *sc1,*sc2; for( sc1 = cs; *sc1 != '\0'; ++sc1) { for( sc2 = ct; *sc2 != '\0'; ++sc2) { if (*sc1 == *sc2) return (char *) sc1; } } return NULL;}#endif#ifndef __HAVE_ARCH_STRTOK/** * strtok - Split a string into tokens * @s: The string to be searched * @ct: The characters to search for * * WARNING: strtok is deprecated, use strsep instead. */char * strtok(char * s,const char * ct){ char *sbegin, *send; sbegin = s ? s : ___strtok; if (!sbegin) { return NULL; } sbegin += strspn(sbegin,ct); if (*sbegin == '\0') { ___strtok = NULL; return( NULL ); } send = strpbrk( sbegin, ct); if (send && *send != '\0') *send++ = '\0'; ___strtok = send; return (sbegin);}#endif#ifndef __HAVE_ARCH_STRSEP/** * strsep - Split a string into tokens * @s: The string to be searched * @ct: The characters to search for * * strsep() updates @s to point after the token, ready for the next call. * * It returns empty tokens, too, behaving exactly like the libc function * of that name. In fact, it was stolen from glibc2 and de-fancy-fied. * Same semantics, slimmer shape. ;) */char * strsep(char **s, const char *ct){ char *sbegin = *s, *end; if (sbegin == NULL) return NULL; end = strpbrk(sbegin, ct); if (end) *end++ = '\0'; *s = end; return sbegin;}#endif#ifndef __HAVE_ARCH_MEMSET/** * memset - Fill a region of memory with the given value * @s: Pointer to the start of the area. * @c: The byte to fill the area with * @count: The size of the area. * * Do not use memset() to access IO space, use memset_io() instead. */void * memset(void * s,int c,size_t count){ char *xs = (char *) s; while (count--) *xs++ = c; return s;}#endif#ifndef __HAVE_ARCH_BCOPY/** * bcopy - Copy one area of memory to another * @src: Where to copy from * @dest: Where to copy to * @count: The size of the area. * * Note that this is the same as memcpy(), with the arguments reversed. * memcpy() is the standard, bcopy() is a legacy BSD function. * * You should not use this function to access IO space, use memcpy_toio() * or memcpy_fromio() instead. */void bcopy(const void * srcp, void * destp, size_t count){ const char *src = srcp; char *dest = destp; while (count--) *dest++ = *src++;}#endif#ifndef __HAVE_ARCH_MEMCPY/** * memcpy - Copy one area of memory to another * @dest: Where to copy to * @src: Where to copy from * @count: The size of the area. * * You should not use this function to access IO space, use memcpy_toio() * or memcpy_fromio() instead. */void * memcpy(void * dest,const void *src,size_t count){ char *tmp = (char *) dest, *s = (char *) src; while (count--) *tmp++ = *s++; return dest;}#endif#ifndef __HAVE_ARCH_MEMMOVE/** * memmove - Copy one area of memory to another * @dest: Where to copy to * @src: Where to copy from * @count: The size of the area. * * Unlike memcpy(), memmove() copes with overlapping areas. */void * memmove(void * dest,const void *src,size_t count){ char *tmp, *s; if (dest <= src) { tmp = (char *) dest; s = (char *) src; while (count--) *tmp++ = *s++; } else { tmp = (char *) dest + count; s = (char *) src + count; while (count--) *--tmp = *--s; } return dest;}#endif#ifndef __HAVE_ARCH_MEMCMP/** * memcmp - Compare two areas of memory * @cs: One area of memory * @ct: Another area of memory * @count: The size of the area. */int memcmp(const void * cs,const void * ct,size_t count){ const unsigned char *su1, *su2; int res = 0; for( su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--) if ((res = *su1 - *su2) != 0) break; return res;}#endif#ifndef __HAVE_ARCH_MEMSCAN/** * memscan - Find a character in an area of memory. * @addr: The memory area * @c: The byte to search for * @size: The size of the area. * * returns the address of the first occurrence of @c, or 1 byte past * the area if @c is not found */void * memscan(void * addr, int c, size_t size){ unsigned char * p = (unsigned char *) addr; while (size) { if (*p == c) return (void *) p; p++; size--; } return (void *) p;}#endif#ifndef __HAVE_ARCH_STRSTR/** * strstr - Find the first substring in a %NUL terminated string * @s1: The string to be searched * @s2: The string to search for */char * strstr(const char * s1,const char * s2){ int l1, l2; l2 = strlen(s2); if (!l2) return (char *) s1; l1 = strlen(s1); while (l1 >= l2) { l1--; if (!memcmp(s1,s2,l2)) return (char *) s1; s1++; } return NULL;}#endif#ifndef __HAVE_ARCH_MEMCHR/** * memchr - Find a character in an area of memory. * @s: The memory area * @c: The byte to search for * @n: The size of the area. * * returns the address of the first occurrence of @c, or %NULL * if @c is not found */void *memchr(const void *s, int c, size_t n){ const unsigned char *p = s; while (n-- != 0) { if ((unsigned char)c == *p++) { return (void *)(p-1); } } return NULL;}#endif
