C字符串处理函数的实现

C字符串处理函数的实现（Linux）#include <stddef.h>char * ___strtok = NULL;char * strcpy(char * dest,const char *src){char *tmp = dest;while ((*dest++ = *src++) != '/0')/* nothing */;return tmp;}char * strncpy(char * dest,const char *src,size_t count){char *tmp = dest;while (count-- && (*dest++ = *src++) != '/0')/* nothing */;return tmp;}char * strcat(char * dest, const char * src){char *tmp = dest;while (*dest)dest++;while ((*dest++ = *src++) != '/0');return tmp;}char * strncat(char *dest, const char *src, size_t count){char *tmp = dest;if (count) {while (*dest)dest++;while ((*dest++ = *src++)) {if (--count == 0)break;}}return tmp;}int strcmp(const char * cs,const char * ct){register signed char __res;while (1) {if ((__res = *cs - *ct++) != 0 || !*cs++) /*is !*cs++ necessary? incase more cmp*/break;}return __res;}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;}char * strchr(const char * s,char c){for(; *s != c; ++s)if (*s == '/0')return NULL;return (char *) s;}size_t strlen(const char * s){const char *sc;for (sc = s; *sc != '/0'; ++sc)/* nothing */;return sc - s;}size_t strnlen(const char * s, size_t count){const char *sc;for (sc = s; *sc != '/0' && count--; ++sc)/* nothing */;return sc - s;}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;}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;}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);}void * memset(void * s,char c,size_t count){char *xs = (char *) s;while (count--)*xs++ = c;return s;}char * bcopy(const char * src, char * dest, int count){char *tmp = dest;while (count--)*tmp++ = *src++;return dest;}void * memcpy(void * dest,const void *src,size_t count){char *tmp = (char *) dest, *s = (char *) src;while (count--)*tmp++ = *s++;return dest;}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; /*12345678*/} /*12345678*/return dest;}int memcmp(const void * cs,const void * ct,size_t count){const unsigned char *su1, *su2;signed char res = 0;for( su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)if ((res = *su1 - *su2) != 0)break;return res;}/** find the first occurrence of byte 'c', or 1 past the area if none*/void * memscan(void * addr, unsigned char c, size_t size){unsigned char * p = (unsigned char *) addr;while (size) {if (*p == c)return (void *) p;p++;size--;}return (void *) p;}void main(void){return;}补充strstrchar *strstr (const char *haystack, const char *needle){char *result = (char *)NULL;if ((haystack != (char *)NULL) && (needle != (char *)NULL)){register int i;int hl = strlen (haystack);int nl = strlen (needle);for (i = 0; i < (hl - nl); i++)if (strncmp (haystack + i, needle, nl) == 0){result = haystack + i;break;}}return (result);}还有 加州大学的：char *strstr(const char *string, const char *substring){ const char *a, *b; b = substring; if (*b == 0) { return (char*)string; } for( ; *string != 0; string += 1){if (*string != *b) { continue; } a = string; while ((*a++ == *b++) && (*b != 0) );if (*b == 0){return (char*) string;}b = substring;}}最后是AT&T:extern char*strstr(register const char* s1, register const char* s2){register intc1;register intc2;register const char*t1;register const char*t2;if (s2){if (!*s2)return (char*)s1;c2 = *s2++;while (c1 = *s1++)if (c1 == c2){t1 = s1;t2 = s2;do{if (!*t2)return (char*)s1 - 1;} while (*t1++ == *t2++);}}return 0;}--------------------------------------------------------------------------http://blog.csdn.net/wzbob/archive/2006/11/10/1377600.aspxc和汇编实现 一些基本字符串处理函数1. 将一个字符串(src)拷贝到另一个字符串(dest)，直到遇到NULL 字符后停止。char *strcpy (char *dest, const char *src){_asm{pushfmov esi,srcmov edi,destcld l1: lodsb stosb test al,al jne l1 popf} return dest; }2.拷贝源字符串count 个字节到目的字符串。char *strncpy (char *dest, const char *src, int count){_asm{pushfmov esi,srcmov edi,destmov ecx,countcld l1: dec ecx js l2 lodsb stosb test al,al jne l1 rep stosb l2: popf}return dest; }3.将源字符串拷贝到目的字符串的末尾处。char *strcat (char *dest, const char *src){_asm {pushfmov esi,srcmov edi,destxor al,almov ecx,0xffffffffcld // 清方向位。repne scasb dec edi l1: lodsb stosb test al,al jne l1 popf}return dest; }4.将源字符串的count 个字节复制到目的字符串的末尾处，最后添一空字符。char *strncat (char *dest, const char *src, int count){_asm {pushfmov esi,srcmov edi,destxor al,almov ecx,0xffffffffcld repne scasb dec edi mov ecx,count l1: dec ecxjs l2 lodsb stosb test al,al jne l1 l2: xor al,al stosb popf}return dest; }5. 将一个字符串与另一个字符串进行比较。int strcmp (const char *csrc, const char *ct){_asm{pushfmov edi,csrcmov esi,ctcld l1: lodsb scasb jne l2 test al,al jne l1 xor eax,eax jmp l3 l2: mov eax,1 jl l3 neg eax l3: popf}}------------------------------------------------------------------------------------1. strlen(),计算字符串长度 int strlen(const char string) { int i=0; while(string[i]) i++; return i; } 2. strcpy(), 字符串拷贝. char *strcpy(char *destination, const char *source) { while(*destinaton++=*source++); return (destination-1); } 3. strcat(), 字符串的连接. char *strcat(char *target,const char *source) { char *original=target; while(*target) target++; // Find the end of the string while(*target++=*source++); return(original); } 4. streql(), 判断两个字符串是否相等. int streql(char *str1,char *str2) { while((*str1==*str2)&&(*str1)) { str1++; str2++; } return((*str1==NULL)&&(*str2==NULL)); } 5. strchr(), 在字符串中查找某个字符. char *strchr(const char *string,int letter) { while((*string!=letter)&(*string)) string++; return (string); } 6. chrcnt(), 计算某个字符在字符串中出现的次数. int chrcnt(const char *string,int letter) { int count=0; while(*string) if(*string==letter)count++; return count; } 7. strcmp(), 判断两个字符串是否相等. int strcmp(const char *str1,const char *str2) { while((*str1==*str2)&&(*str1)) { str1++; str2++; } if((*str1==*str2)&&(!*str1)) //Same strings return o; else if((*str1)&&(!*str2)) //Same but str1 longer return -1; else if((*str2)&&(!*str1)) //Same but str2 longer else return((*str1>*str2)?-1:1); }