重写 strchr

char * strchr_ex(char * strDst, char c){assert(strDst);if (!strDst)return NULL;while (*strDst != '\0' && *strDst != c)strDst++;return *strDst == c ? strDst : NULL;}char * strrchr_ex(char * strDst, char c){assert(strDst);if (!strDst)return NULL;char * p = strDst;while (*p++ != '\0');p -= 2;while (*p != '\0' && *p != c)p--;return *p == c ? p : NULL;}