Question

I’m trying to write a tic tac toe game in C++, but whenever I run it I get an error message saying:

TicTacToe.cpp: In instantiation of ‘void copy_array(T*, T*) [with T = std::basic_string<char>]’:
TicTacToe.cpp:115:25:   required from here
TicTacToe.cpp:93:3: error: no match for ‘operator*’ in ‘**(new_arr + ((sizetype)(((long unsigned int)i) * 8ul)))’

It points to this function:

86    template<class T>
87    void copy_array(T old_arr[], T *new_arr)
88    {
89      int size = sizeof(old_arr)/sizeof(old_arr[0]);
90      for(int i = 0; i < size; i++)
91      {
92          *new_arr[i] = old_arr[i];
93      }
94    }

An this piece of code:

114    string copy[9];
115    copy_array(board, copy);

Could anyone please explain to me what’s causing the error and how to solve it?

Answer 1

That error message is quite strange, it appears to be printing out a transformed version of your code, but I’m pretty sure it’s referring to this line:

*new_arr[i] = old_arr[i];

Remove the * and you should be fine.

Although of course it won’t function as you expect. Your argument T old_arr[] is going to act exactly like T *old_arr. Notably, sizeof(), which you’re relying on to give you the full size of the array, won’t.

You could use the following template to get around this:

template<class T, int N>
void copy_array(T (&old_arr)[N], T *new_arr) {
    for (int i = 0; i < N; i++) {
        new_arr[i] = old_arr[i];
    }
}

Or, if you can use C++11, you could switch to std::array<>, which knows its size.