C++ Constructor initialization list with array

Question

What am I doing wrong here? The compiler tells me it is a syntax error.

class Color {
private:
    float rgba[4];
public:
    Color(float red, float green, float blue, float alpha=1.0):
            this->rgba[0] (red * alpha),
            this->rgba[1] (green*alpha)
            this->rgba[2] (blue*alpha)
    {

    }
};

I know this is probably just a homework exercise. But check if your graphics lib really wants RGBA pre-multiplied by A — Martin Beckett
– Martin Beckett, Commented Mar 2, 2016 at 18:32
Is it a bad idea to multiply by A? Could you please tell me more about it? — happy_sisyphus
– happy_sisyphus, Commented Mar 2, 2016 at 18:35
The reason for the "A" is to change the all the colors at once, to handle overlaying images etc. Normally the graphics hardware would do the multiplication at display time. — Martin Beckett
– Martin Beckett, Commented Mar 2, 2016 at 18:39
this->rgba[0] is an error. The only thing that can appear after : is a member identifier, i.e. rgba is the only option for this class — M.M
– M.M, Commented Mar 2, 2016 at 21:19

Jarod42 · Accepted Answer · 2016-03-02 18:30:41Z

4

It should be

Color(float red, float green, float blue, float alpha=1.0):
            rgba{red * alpha, green*alpha, blue*alpha, 0}
    {

    }

answered Mar 2, 2016 at 18:30

Jarod42

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2 Comments

David Hammen Over a year ago

This assumes a C++11 compliant compiler. Some people still aren't using C++11.

M.M Over a year ago

Some people haven't discovered computers yet so we should print this answer out and do a leaflet drop

Andrés Guerrero · Accepted Answer · 2016-03-02 23:41:33Z

0

You can use the asigment operator instead of parentetheses:

this->rgba[0](red * alpha) // wrong
this->rgba[1] = red * alpha // ok

answered Mar 2, 2016 at 23:41

Andrés Guerrero

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