C++ Dynamic Array Write Access Violation

Question

This has been bugging me for almost 2 days now. I have in my class definition a 2-D dynamic array:

class Raster {

public:
    int pixels[][4];

    void drawTriangle(Vector2f & V1, Vector2f & V2, Vector2f & V3, PixelColor & colorA, PixelColor & colorB, PixelColor & colorC);

};

In my drawing method I have this loop

for (int Y = maxY; Y >= minY; Y--) {
    for (int X = minX; X <= maxX; X++) {
        float lambda1;
        float lambda2;
        float lambda3;
        triangle.getBarycentricCoordinate(X, Y, &lambda1, &lambda2, &lambda3);
        if ((0.0f <= lambda1 && 0.0f <= lambda2 && 0.0f <= lambda3)) {
            PixelColor a = lambda1 * colorA;
            PixelColor b = lambda2 * colorB;
            PixelColor c = lambda3 * colorC;
            PixelColor interpolatedColor = a + b + c;
            pixels[Y*width + X][0] = interpolatedColor.R;
            pixels[Y*width + X][1] = interpolatedColor.G;
            pixels[Y*width + X][2] = interpolatedColor.B;

        }
    }
}

Can anyone point out why it is wrong? Here is the error message: "Exception thrown: write access violation. this was 0x111013530C28FA2."

That's not a copy constructor, but OK. That declaration doesn't allocate any storage for pixels. What you have is effectively an array of size 0. — melpomene
– melpomene, Commented Feb 2, 2018 at 4:31
@ManhNguyenHuu -- int pixels[][4]; -- I wish gcc turned off this option by default. It isn't C++, and all it does is lead persons down the wrong path. If you want a dynamic array, use std::vector. — PaulMcKenzie
– PaulMcKenzie, Commented Feb 2, 2018 at 5:01

AndreyS Scherbakov · Accepted Answer · 2018-02-02 04:30:02Z

0

pixels[][2] doesn't define a non-zero length array here. You need to specify a number for the first dimension too.

edited Feb 2, 2018 at 4:30

answered Feb 2, 2018 at 4:20

AndreyS Scherbakov

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Vishaal Shankar · Accepted Answer · 2018-02-02 06:02:34Z

0

I don't think that's a dynamic array.

When you declare an array you are required to declare it's size as well. You can tell what kind of array it is by what you create it as and what the data is. For instance in the following code :

// Here we can see that the array is a 4X3.
int pixels[][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12} };

This would work just fine, because the size of the array is understood.

Further i would like to add that if you really want something not restrained by size and want the size to be dynamic depending on the data you have, then you could use the various containers that Standard Template Library offers such as a std::vector.

edited Feb 2, 2018 at 6:02

answered Feb 2, 2018 at 5:09

Vishaal Shankar

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