默认参数：在非静态成员函数外部无效使用“ this”

Question

I try to have a default parameter in my functions but the compiler says there is an error :

invalid use of 'this' outside of a non-static member function

How can I fix this ?

Edit : @RSahu, here is the two overloaded functions, can you explain me how I can manage the problem because apparently I didn't understand how to fix it.

Game.hpp :

class Game {
 private :
  int** board;

  vector<pair <int, int> > listPiecesPosition();
  vector<pair <int, int> > listPiecesPosition(int** board);

  // What doesn't work
  vector<pair <int, int> > listPiecesPosition(int** board = this->board); 

Game.cpp :

//Here I need to write more or less two times the same function, how can I do it only once ?

   vector<pair <int, int> > Game::listPiecesPosition() {
vector<pair <int, int> > listPiecesPosition;
for (int i=0; i < getSize(); i++)
  for (int j=0; j < getSize(); j++)
    if (getBoard()[i][j] == nextPlayer.getColor()) // Here I don't use the parameter
      listPiecesPosition.push_back(make_pair(i,j));
return listPiecesPosition;
  }

  vector<pair <int, int> > Game::listPiecesPosition(int** board) {
    vector<pair <int, int> > listPiecesPosition;
    for (int i=0; i < getSize(); i++)
      for (int j=0; j < getSize(); j++)
        if (board[i][j] == nextPlayer.getColor()) // Here I use the parameter
          listPiecesPosition.push_back(make_pair(i,j));
    return listPiecesPosition;
  }

Thanks for you help !

Answer 1

this can be used only inside the body of a non-static member function. Hence, your use of this->board as the default value of the input is not correct.

I suggest creating an overload to get around the problem.

class Game {
 private :
  int** board;

  vector<pair <int, int> > listPiecesPosition(int** board);
  vector<pair <int, int> > listPiecesPosition()
  {
     return listPiecesPosition(this->board);
  }

PS this can appear outside the body of a member function in limited contexts. This is not one of those situations.

Update, in response to OP's comment

Change

vector<pair <int, int> > Game::listPiecesPosition() {
   vector<pair <int, int> > listPiecesPosition;
   for (int i=0; i < getSize(); i++)
      for (int j=0; j < getSize(); j++)
         if (getBoard()[i][j] == nextPlayer.getColor()) // Here I don't use the parameter
            listPiecesPosition.push_back(make_pair(i,j));
   return listPiecesPosition;
}

to

vector<pair <int, int> > Game::listPiecesPosition() {
   return listPiecesPosition(this->board);
}

By doing this, you avoid duplication of code that implements the main logic of the functions.