Question

Here is my code:

bool Character::keyPress(char c)
{
    switch(c)
    {
        case up_key:
            move(0, -1);
            break;

        case down_key:
            move(0, 1);
            break;

        case left_key:
            move(-1, 0);
            break;

        case right_key:
            move(1,0);
            break;

        default:
            return false;
    }

    return true;
}

And the compiler complains:

error C2051: case expression not constant
error C2051: case expression not constant
error C2051: case expression not constant
error C2051: case expression not constant

In my header file I have:

protected:
    char up_key;
    char down_key;
    char right_key;
    char left_key;

I am using Visual C++ 2008.

Answer 1

As the error message states, the case expressions must be constant. The compiler builds this as a very fast look-up table at compile time and it can’t do that if there is a possibility that the values could change as the program runs.

If you do need them to be variable, not constant, your best bet is to use if/else statements instead.