<2012 12 17> C标准库中一些字符串操作函数的实现
2012-12-17 21:27
495 查看
刚学C语言的时候经常做这样的题,比如实现strcpy strcat库函数的内部实现,有的公司笔试也会考这些。截自linux内核中的lib/string.c文件,绝对标准的程序,供大家参考。
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. */ void *memset(void *s, int c, size_t count) { char *xs = s; while (count--) *xs++ = c; return s; } 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. */ void *memcpy(void *dest, const void *src, size_t count) { char *tmp = dest; const char *s = src; while (count--) *tmp++ = *s++; return dest; } 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; const char *s; if (dest <= src) { tmp = dest; s = src; while (count--) *tmp++ = *s++; } else { tmp = dest; tmp += count; s = src; s += count; while (count--) *--tmp = *--s; } return dest; } 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; } 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'); return tmp; } 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 * * The result is not %NUL-terminated if the source exceeds * @count bytes. * * In the case where the length of @src is less than that of * count, the remainder of @dest will be padded with %NUL. */ char *strncpy(char *dest, const char *src, size_t count) { char *tmp = dest; while (count) { if ((*tmp = *src) != 0) src++; tmp++; count--; } return dest; } 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; } 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) { while (*dest) dest++; while ((*dest++ = *src++) != 0) { if (--count == 0) { *dest = '\0'; break; } } } return tmp; } strcmp: /* * strcmp - Compare two strings * @cs: One string * @ct: Another string */ int strcmp(const char *cs, const char *ct) { unsigned char c1, c2; while (1) { c1 = *cs++; c2 = *ct++; if (c1 != c2) return c1 < c2 ? -1 : 1; if (!c1) break; } return 0; } 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) { unsigned char c1, c2; while (count) { c1 = *cs++; c2 = *ct++; if (c1 != c2) return c1 < c2 ? -1 : 1; if (!c1) break; count--; } return 0; } 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; } 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); return sc - s; } 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); return sc - s; } 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. */ char *strsep(char **s, const char *ct) { char *sbegin = *s; char *end; if (sbegin == NULL) return NULL; end = strpbrk(sbegin, ct); if (end) *end++ = '\0'; *s = end; return sbegin; } 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; }
相关文章推荐
- 一些字符串及内存操作函数的实现
- <2012 12 17> linux驱动中的platform总线架构(含具体IIC设备驱动)
- 一些字符串操作函数的模拟实现
- 一些常用字符串操作函数的内部实现
- C标准库函数实现之字符串操作
- 一些常用字符串操作函数的内部实现
- <2012 12 17> Why ARM's EABI Matters?有关ARM-Linux平台浮点计算性能。
- 走进C标准库(8)——"string.h"中函数的实现相关字符串操作函数
- 一些字符串及内存操作的函数的实现
- 字符串 操作函数 strchr 实现
- Postgresql数据库的一些字符串操作函数
- <转载>C#中父窗口和子窗口之间实现控件互操作
- 一些字符串处理函数的实现!
- C标准库函数实现之字符串比较函数
- Linux下文件读写操作一例(C标准库函数方式实现)
- C语言中操作字符串的一些函数源代码[转]
- 字符串的一些常用操作函数
- 黑马程序员<.net中安全处理字符串的一些方法>
- H面试程序(0):字符串一些常用函数的实现
- C 语言中操作字符串的一些函数源代码(对比版)