Why does this simple loop crash?

Question

The following code crashes when compiled with MS VC 2013 Express (Windows 7, 64 bit computer):

#include <iostream>

#define N 1000*1000



int main()

{

  float x[N];

  int i;

  for (i = 0; i < N; i++) 

    x[i] = (float) (rand() + 1) / RAND_MAX;

}

What is wrong? Is it a memory problem?

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Answer 1

You're basically trying to allocate an array of 1000000 elements, which is simply too big. It's just too huge for programs stack space.

Result: Stack overflow.

Side effect: Undefined behavior, crash.

Solution: Allocate that array in heap. Take a pointer, allocate memory using memory allocator function and you may be able to get it going.

Though arrays are not pointers but for most of the cases, a replacement like (in C)

float * x = malloc(N * (sizeof *x)); // for simplicity, omitting obligatory free, 
                                     // success check, stdlib inclusion etc.

would work.

That said, the actual solution would be, re-plan the program design, normally you should not be needing an array that large, try to make the design more modular and process in parts, as and when required.

Why does this simple loop crash?

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