一天一個CRT函數 strstr

1.介紹

char *strstr( const char *str, const char *strSearch );

需找str字符串中出現strSearch字符串位置的指針。如果沒找到，則返回NULL，如果strSearch爲空，則返回str。

2.實現

inline tChar *tStrStr(tChar *pStr, tChar *pSubStr)
{
/* First scan quickly through the two strings looking for a
    * single-character match.  When it's found, then compare the
    * rest of the substring.
    */

    tChar *b = pSubStr;
if( *b == NULL )
    {
return pStr;
    }

    tChar *a = NULL;
for( ; *pStr != NULL; pStr++) 
    {
if( *pStr != *b ) 
        {
continue;
        }

        a = pStr;
while(1) 
        {
if( *b == NULL ) 
            {
return pStr;
            }
if( *a++ != *b++ ) 
            {
break;
            }
        }

        b = pSubStr;
    }

return NULL;
}

其實，也就是雙重循環比較。

 

3.測試

tChar str[] =    _T("lazy");
tChar string[] = _T("The quick brown dog jumps over the lazy fox");

tChar *pdest = NULL;
int  result = 0;

pdest = CY_CRT::tStrStr( string, str );
result = (int)(pdest - string + 1);

4.後記

CRT提供了strstr外，還有strrstr，即反序查找。

當然，STL裏也有提供類似的算法—find_fist_of/find_last_of/find_first_not_of/find_last_not_of.