CODEWITHSUNDEEP
c++vectorsizemember
Izaan
Izaan

Reputation: 535

Unable to specify initial size of vector

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;
}

Upvotes: 6

Views: 9847

Answers (2)

user2591612
user2591612

Reputation:

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;
};

Upvotes: 7

juanchopanza
juanchopanza

Reputation: 227370

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);

Upvotes: 12

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