String function & macros C++(user defined)

#define LL long long
#define VS vector<string>

//string related
#define str_to_int(StrToInt)       atoi(StrToInt.c_str())
#define str_to_LL(StrToLL)         atoll(StrToLL.c_str())
#define str_to_double(StrToDouble) atof(StrToDouble.c_str()
VS split_string(const string str, const string _dlm) {
    VS tokens; size_t prev = 0, pos = 0;
    do{
        pos = str.find(_dlm, prev);
        if (pos == string::npos) pos = str.sz;
        string token = str.substr(prev, pos-prev);
        if (!token.empty()) tokens.pb(token);
        prev = pos + _dlm.sz;
    }while (pos < str.sz && prev < str.sz);
    return tokens;
}
template <typename T> string toString(T n) { stringstream ss; ss << n; return ss.str(); }