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 != ‘′) {

pSubString++;

pPareString++;

}

if(*pSubString == ‘′) return pTmp;

}

return NULL;

}

int main(int argc, char* argv[]) {

char *ParentString = “happy birthday to you!”;

char *SubString = “birthday”;

printf(“%s”,strstring(ParentString, SubString));

}