Unable to specify initial size of vector

Question

I have a class called ChessBoard and one of the member variables is

std::vector<ChessPiece *> pieces(16);

This is giving me an "expected a type specifier" error. The default constructor of ChessPiece is private. However, if I write the same statement inside a function it works perfectly (i.e. the initial size of pieces is 16). Why is it reporting an error when I try to specify initial size of a member variable? Thanks!

SSCCE:

class ChessPiece {

    ChessPiece();

public:
    ChessPiece(int value) { std::cout << value << std::endl; }
};

class ChessBoard {

    ChessBoard();
    std::vector<ChessPiece *> pieces(16); // Error: expected a type specifier

public:
    ChessBoard(int value) { std::cout << value << std::endl; }
};

int main(int argc, char*argv[]) {

    std::vector<ChessPiece *> pieces(16);
    std::cout << pieces.size() << std::endl; // prints 16
    std::cin.get();
    return 0;
}

juanchopanza · Accepted Answer · 2014-07-15 21:33:02Z

12

The required syntax for in-place initialization of data members does not allow the () initialization syntax common with non-members. You can use this syntax instead:

std::vector<ChessPiece*> pieces = std::vector<ChessPiece*>(16);

edited Jul 15, 2014 at 21:33

answered Jul 15, 2014 at 21:19

juanchopanza

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Comments

score 7 · Accepted Answer · 2014-07-15 21:36:34Z

7

You can't call a method on a member variable inside your class declaration.

In your cpp file you could do something like:

ChessBoard::ChessBoard() { pieces.resize(16); }

or:

ChessBoard::ChessBoard(): pieces(16) {}

The second one calls the vector constructor that takes a size argument. Or you can directly do it in your .h file:

class ChessBoard {
    ChessBoard(): pieces(16) {} // version 1
    ChessBoard(): pieces() { pieces.resize(16); }  // version 2

private:
    std::vector<ChessPiece *> pieces;
};

edited Jul 15, 2014 at 21:36

answered Jul 15, 2014 at 21:17

user2591612

8 Comments

juanchopanza Over a year ago

Your first ChessBoard constructor looks wrong. Maybe you mean ChessBoard(): pieces(16) {}?

user2591612 Over a year ago

@juanchopanza: Whoops, fixed. Thank you

Izaan Over a year ago

I may be wrong but wouldn't pieces.resize(16) throw an error since the default constructor is inaccessible?

user2591612 Over a year ago

@IzaanSiddiqi: How is it inaccessible?

Izaan Over a year ago

Sorry, I made a mistake somewhere else and it's working now. Thank you both for your help!

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