C++ array in class not initializing properly

Question

I'm making a monopoly game, and I have two arrays of Vectors for coordinates for my 2d array of characters. Below is my board.h where the array is kept in the board class

class Board {
    ...
    Vector propList[40];
    Vector coordList[40];
    ...
public:
    ...
};

I am getting an error running my program in bash when trying to create the executable, displayed below (there are 2 identical errors for each array)

board.cc:15:8: error: constructor for 'Board' must explicitly initialize the member 'propList' which does not have a default constructor
Board::Board() {
       ^
./board.h:17:12: note: member is declared here
    Vector propList[40];

I have all 40 elements initialized in my board constructor as displayed below

propList[0] = Vector(-1, -1);
propList[1] = Vector(73, 51);
...
propList[39] = Vector(81, 46);

coordList[0] = Vector(81, 54);
coordList[1] = Vector(73, 54);
...

I also tried the following

Vector v = (-1, 1);
propList[0] = v;
...

and receive the same error. Does anybody know what is going on and how to fix it?

edit: I forgot to add my vector code. I had to create a constructor since I can't use C++11 initialization on my computer.

vector.cc
#include "vector.h"
Vector::Vector(int x, int y) : x(x), y(y) {}

vector.h
struct Vector {
    Vector(int x, int y);
    int x;
    int y;
};

Your Vector class requires arguments be passed to the consturctor. — Chad
– Chad, Commented Nov 30, 2014 at 23:30
Was the "...which does not have a default constructor" part of the error message not clear enough? Vector doesn't have a default constructor. It ether needs one or you need a different initialization approach. — WhozCraig
– WhozCraig, Commented Nov 30, 2014 at 23:30
@WhozCraig sorry I didn't add my vector code. I needed to create a constructor because I can't use c++11 initialization. — Hayden
– Hayden, Commented Nov 30, 2014 at 23:35

tenfour · Accepted Answer · 2014-11-30 23:55:39Z

1

In your constructor, these are assignments, not initialization. Constructors have an initialization list specifically for this purpose. Unfortunately, you can't initialize arrays like this.

Here's the initialization list for a simple int member:

class MyClass
{
    int myField;

    MyClass() :
        m_myField(1)// initialization
    {
        // right here, myField is 1.
        myField = 2;// assignment.
    }
};

This initializes myField to 1. Then assigns 2, like you're doing in your constructor.

You can't initialize arrays like this, so I would recommend a workaround: A std::vector of Vectors. Yea that's confusing because both are called "vector", but they mean different things. std::vector is a storage container.

std::vector<Vector> propList;

and in your constructor, add Vector objects to the propList

Board::Board()
{
    propList.push_back(Vector(-1, -1));
    propList.push_back(Vector(73, 51));
    ...
}

Another solution is to add a default constructor to Vector. But that's a bit dirty compared to using std::vector<>.

~~In C++11 it may be possible using aggregate initialization in a constructor initialization list.~~ No, it's not possible, period.

edited Nov 30, 2014 at 23:55

answered Nov 30, 2014 at 23:35

tenfour

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1 Comment

Richard Hodges Over a year ago

is this a description of the board or the state of play? A monopoly board is a prime candidate for a static const array of Vector, which can certainly be list-initialised.

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