实现strstr功能，即在父串中寻找子串首次出现的位置

实现strstr功能，即在父串中寻找子串首次出现的位置。（笔试中常让面试者实现标准库中的一些函数）
char * strstring(char *ParentString, char *SubString) {
char *pSubString, *pPareString;
for(char *pTmp=ParentString; *pTmp; pTmp++) {
pSubString = SubString;
pPareString = pTmp;
while(*pSubString == *pPareString && *pSubString != ‘\0′) {
pSubString++;
pPareString++;
}
if(*pSubString == ‘\0′) return pTmp;
}
return NULL;
}

int main(int argc, char* argv[]) {
char *ParentString = “happy birthday to you!”;
char *SubString = “birthday”;
printf(“%s”,strstring(ParentString, SubString));
}