C语言字符串查找的几种实现

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/*********************************************************************
* Author : Samson
* Date    : 01/09/2012
* Test platform:
*               GNU Linux version 2.6.29.4
*               gcc version 4.4.0 20090506 (Red Hat 4.4.0-4) (GCC)

* *******************************************************************/

/* locate a substring */

char * _strstr(char *s1, char *s2)
{
   char c1, c2;
   int sublen = _strlen(s2);

   c2 = *s2++;

   do
   {

       do
       {
           c1 = *s1++;

           if(0 == c1)
               return NULL;

       }while(c1 != c2);

   }while(_strncmp(s1, s2, sublen));

   return --s1;
}

/* locate substring of N characters */

char * _strstrn(char *s1, char *s2, int n)
{
       char c1, c2;

       c2 = *s2++;

       do
       {
               do
               {
                   c1 = *s1++;

                   if(0 == c1)
                   {
                       return NULL;
                   }
               }while(c1 != c2);

       }while(_strncmp(s1, s2, n - 1));

       return --s1;
}

/* locate substring of N characters and Ignore case*/

unsigned char * _strnocasestrn(unsigned char *s1, unsigned char *s2, int n)
{
       unsigned char c1, c2;

       c2 = *s2++;
       (c2 >= 'A' && c2 <= 'Z') ? (c2 | 0x20) : c2;

       do
       {

           do
           {
               c1 = *s1++;
               if(0 == c1)
                   return NULL;

               c1 = (c1 >= 'A' && c1 <= 'Z') ? (c1 | 0x20) : c1;
           }while(c1 != c2);

       }while(_strncmp(s1, s2, n - 1) != 0);

   return --s1;

}

以上实现中的_strncmp请参照http://blog.csdn.net/yygydjkthh/article/details/7188518中的具体实现