Stack overflow C++

This is my code. When I access dtr array in initImg function it gives a stack overflow exception. What might be the reason?

#define W 1000
#define H 1000
#define MAX 100000 
void initImg(int img[], float dtr[])
{
    for(int i=0;i<W;i++)
        for(int j=0;j<H;j++)
            img[i*W+j]=255;

    for(int j=0;j<H;j++)
    {
        img[j] = 0;
        img[W*(W-1)+j] = 0;
    }
    for(int i=0;i<W;i++)
    {
        img[i*W] = 0;
        img[i*W+H-1] = 0;
    }
    for(int i=0;i<W;i++)
        for(int j=0;j<H;j++)
        { 
            if(img[i*W+j]==0)
                dtr[i*W+j] = 0;    // <------here
            else
                dtr[i*W+j] = MAX;  // <------here
        }
}
int main()
{
    int image[W*H];
    float dtr[W*H];
    initImg(image,dtr);
    return 0;
}

Solution 1:

This:

int image[W*H];
float dtr[W*H];

Creates each a 4 * 1000 * 1000 ~ 4 MB array into the stack. The stack space is limited, and usually it's less than 4 MB. Don't do that, create the arrays in the heap using new.

int *image = new int[W*H];
float *dtr = new float[W*H];

Solution 2:

Your stack probably isn't big enough to hold a million ints and a million floats (8MB). So as soon as you try to access beyond your stack size, your operating system throws you an error. Objects or arrays above a certain size need to be allocated on the heap - preferably using a self-managing self-bounds-checking class such as std::vector - the specific size depends on your implementation.

Solution 3:

In addition to the stack overrun, you have another problem -- one which is masked by your definitions of W and H.

for(int i=0;i<W;i++)
    for(int j=0;j<H;j++)
    { 
        if(img[i*W+j]==0)
            dtr[i*W+j] = 0;    // <------here
        else
            dtr[i*W+j] = MAX;  // <------here
    }

Your i loop should count from 0 to H-1, rather than W-1 (and the j loop should swap as well). Otherwise your code will only work correctly if W==H. If WH you will overrun your buffers.

This same problem exists elsewhere in your code sample as well.

Solution 4:

You're creating giant arrays on the stack. Just use std::vector instead:

std::vector<int> image(W*H);
std::vector<float> dtr(W*H);

Solution 5:

Your stack is full. You can allocate memory in heap or increase the stack memory. From what I know the maximum size is about 8MB, but this is not a very good idea. The best solution is to use heap allocation or some containers (vector) available in std.