Is there any limitation on the maximum size of array in c? [duplicate]

Answer 1

When you use expressions like unsigned char idata[sz1][sz2], the space of the array is allocated in stack, while the space of the stack is somehow really small, which causes you problem.

But if you use unsigned char* idata = new char*[sz], the space needed is allocated on the heap. Usually you can get the space you want.

Answer 2

If you declare this on stack (e.g. in some function) then yes, it will provide stack overflow.

You can declare it as static ('global variable') or allocate memory dynamically.

The Using malloc for allocation of multi-dimensional arrays with different row lengths question is pretty much about it.

Answer 3

I am guessing that idata is a local variable. The problem is that local variables are stored on the stack (technically "automatic storage"), and the stack is much smaller than the 6400 megabytes you're trying to allocate on it. Allocating that much storage on it causes a stack overflow.

Try

unsigned char** idata = new unsigned char*[DIM1];

for (int i = 0; i < DIM1; ++i)
    idata[i] = new unsigned char[DIM2];

// or

unsigned char (*idata)[DIM2] = new char[DIM1][DIM2];

To allocate it in the free store and you shouldn't have a problem.

EDIT:

I just looked at the tags and didn't see you were only talking about C. If so, you can do the same thing but use malloc instead of new:

unsigned char** idata = malloc(sizeof(unsigned char*) * DIM1);

for (i = 0; i < DIM1; ++i)
    idata[i] = malloc(DIM2);

// or

unsigned char (*idata)[DIM2] = malloc(DIM1 * DIM2);

And don't forget to free (or delete[] for C++) the memory you allocate to avoid memory leaks.

Answer 4

Here is how you allocate and free a 2D array on the free store in C:

unsigned char (*idata)[1400] = malloc(1600 * 1400);
// ...
free(idata);