C字符串操作函数的实现

#include <stdio.h>#include <stdlib.h>#include <string.h>/*******string库函数集合********/int my_strlen(const char *str){ int ret = 0; assert(str != NULL); while(*str++ != '\0')  ++ret; return ret;}/*******不得自定义变量*********/int my_strlen2(const char *str){ if((*str) == '\0')  return 0; else  return (1 + my_strlen(++str));}//=========字符串查找=========//char *my_strstr(char *strSrc, char *substr){ int i, j; int lenstr, sublen; int num; if(strSrc == NULL || substr == NULL)  return NULL; lenstr = strlen(strSrc); sublen = strlen(substr); if(lenstr < sublen)  return NULL; num = lenstr - sublen; for(i = 0; i <= num; i++) {  for(j = 0; j < sublen; j++)  {   if(strSrc[i+j] != substr[j])    break;  }  if(j == sublen)   return (strSrc + i); } return NULL;}char *my_strstr2(const char *strSrc, const char *str){ assert(strSrc != NULL && str != NULL); const char *s = strSrc; const char *t = str; for(; *strSrc != '\0'; ++strSrc) {  for( s= strSrc, t = str; (*t != '\0') && (*s == *t); ++s, ++t )  {  }  if(*t == '\0')   return (char *)strSrc; } return NULL;}//=========字符串拷贝=========//char *my_strcpy(char *strDst, char *strSrc){ if(strDst == strSrc)  return strDst; assert( (strDst != NULL) && (strSrc != NULL) ); char *address = strDst; while( (*strDst++ = *strSrc++) != '\0'); return address;}char *my_strncpy(char *strDst, char *strSrc, int count){ assert(strDst != NULL && strSrc != NULL); char *address = strDst; while((count--) && (*strSrc != '\0'))  *strDst ++ = *strSrc++; *strDst = '\0'; return address;}//==========字符串链接=========//char *my_strcat(char *strDst, const char *strSrc){ assert((strDst != NULL) && (strSrc != NULL)); char *address = strDst; while(*strDst != '\0')  ++ strDst; while((*strDst++ = *strSrc++) != '\0'); return address;}char *my_strncat(char *strDst, const char *strSrc, unsigned int count){ assert((strDst != NULL) && (strSrc != NULL)); char *address = strDst; while(*strDst != '\0')  ++strDst; while(count-- && *strSrc != '\0')  *strDst++ = *strSrc++; *strDst = '\0'; return address;}//=========将字符串所有替换成字符=========//char *my_strset(char *str, int c){ assert(str != NULL); char *s = str; for(; *s != '\0'; ++s)  *s = (char)c; return str;}char *my_strnset(char *str, int c, unsigned int count){ assert(str != NULL); char *s = str; for(; (*s != '\0') && ((s - str)<count); ++s)  *s = (char) c; return str;} //=====================================================// 题目：比较2个字符串，用O(n)时间和恒量空间//=====================================================int my_strcmp(const char *str1, const char *str2){ while((*str1 != '\0') && (*str2 != '\0') && (*str1 = *str2)) {  str1++;  str2++; } return (*str1 - *str2);}int my_strncmp(const char *str1, const char *str2, unsigned int count){ assert((str1 != NULL) && (str2 != NULL)); while(*str1 && *str2 && (*str1 == *str2) && count--) {  ++ str1;  -- str2; } return (*str1 - *str2);}//===========查找字符出现的位置============//char *my_strrchr(const char *str, int c){ assert(str != NULL); const char *s = str; while(*s != '\0')  ++ s; for(--s; *s != (char)c; --s) {  if(s == str)   return NULL; } return (char *)s;}//===========字符串的逆序============//char my_strrev(char *str){ assert(str != NULL); char *s = str, *t = str, c; while(*t != '\0')  ++t; for(--t; s < t; ++s, --t) {  c = *s;  *s = *t;  *t = c; } return str;}//=========字符串的切割==========//char *my_strtok(char *strToken, const char *str){ assert(str != NULL); static char *last; if(strToken == NULL && (strToken = last)==NULL)  return (NULL); char *s = strToken; const char * t = str; while(*s != '\0') {  t = str;  while(*t != '\0')  {   if(*s == *t)   {    last = s + 1;    if(s - strToken == 0)    {     strToken = last;     break;    }    *(strToken + (s - strToken))= '\0';    return strToken;   }   ++t;  }  ++s; } return NULL;}//=========内存拷贝========//void my_memcpy(void *dst, const void *src, unsigned int num){ assert((dst!=NULL) && (src != NULL)); void *address = dst; while(num--) {  *(char *)dst = *(char *)src;  dst = (char *)dst + 1;  src = (char *)src + 1; } return address;}//===========内存清零=========//void *my_memset(void *str, int c, unsigned int count){ assert(str != NULL); void *s = str; while(count --) {  *(char *)s = (char)c;  s = (char *)s + 1; } return str;}//=====================================================// 题目：在给定的字符串中查找【由给定字符ch构成的】长度最长的串// 分析：例如在abccdefaaag中长度最长的是aaa// 返回值：查找串的首地址//=====================================================char *search_str_maxlen(char *strSrc, char ch){ char *strTemp = NULL, *strDst = NULL; int iTemp, iCount = 0; while(*strSrc != '\0') {  if((*strSrc) == ch)  {   iTemp = 0;   strTemp = strSrc;   while((*strSrc) == ch)   {    strSrc++;    iTemp++;   }   if(iTemp > iCount)   {    iCount = iTemp;    strDst = strTemp;   }   if((*strSrc)=='\0')    break;  }  strSrc++; } return strDst;}//========================================================// 题目：在一个字符串中找到第一个只出现一次的字符。如输入abaccdeff，则输出b。// 分析：这道题是2006 年google 的一道笔试题。// 思路：将所有出现的字符的个数存储在数组a中//========================================================char first_single_char(char *str){ int a[255]; char *p = str; memset(a, 0, 255*sizeof(int)); while(*p != '\0') {  a[*p] ++;  p++; } p = str; while((*p) != '\0') {  if(a[*p] == 1)   return *p; } return '\0';}花了一个下午，终于搞定。