/*
Description:
The strstr function locates the firstoccurrence in the string pointed to by s1 of the sequence of characters(excluding the terminating\
null character)in the string pointed to by s2.
Returns:
The Strstr function returns a pointer to the located string,or a null pointer if the string is not found.If s2 points to a string with\
zero length,the function return str1.
*/
char *Strstr(char *str1, char *str2)
{
while(*str1)
{
char *pos = str1;
char *s2 = str2;
while(*s2 && *pos && (*pos == *s2))
{
pos++;
s2++;
}
if(!*s2)
return str1;
if(!*pos)
return NULL;
str1++;
}
return NULL;
}
/*
Description:
在str1字符串中，同时在span个字符内，定位tr2, 如果search str1的过程中，超出了span的范围，即遍历str1中的字符个数超过了span，则查找失败，返回null。
Returns:
The Strstr function returns a pointer to the located string,or a null pointer if the string is not found.If s2 points to a string with\
zero length,the function return str1.
*/
char *StrstrSpan(char *str1, char *str2, int span)
{
while(*str1 && span)
{
char *pos = str1;
char *s2 = str2;
while(*s2 && *pos && (*pos == *s2) && pos < str1 + span)
{
pos++;
s2++;
}
if(!*s2)
return str1;
if(!*pos || pos >= str1 + span)
return NULL;
str1++;
span--;
}
return NULL;
}