Vector element to char*

Is there a simpler method?

Code:

        vector<string> Size;
        char *s = strdup(Size[i].c_str());
        long long num = _strtoi64(s, NULL, 10);

If your standard library implementation conforms sufficiently to C++11, you could write:

Code:

vector<string> Size;
// ...
long long num = stoll(Size[i]);

You don't need char* in the first place. _strtoi64 (which is bad function to use, btw) takes a const char*, because it doesn't change its parameters. Therefore, simply calling c_str() should suffice.
Also, to duplicate a string, all you need is to simply declare another string and assign the old one to it.