Extensive matrix makes the program stop working

Question

I have the following problem, when I define a matrix that is very large, for example: int matriz[2000][2000], compile and run, the program stops working. I tested only on Windows and it appears that classic message "*.exe has stopped working".

#include <stdio.h>

int main() {
    int matriz[2000][2000];
    return 0;
}

This is the code as you can see I just declare matrix, and that’s enough to stop working at the time of execution. If I decrease the size works, I’ve tested it, but I need a gigantic matrix even.

I’m using the windows 7 professional. IDE DEV-C++; gcc compiler 4.8.1 32 bits

Answer 1

Are you getting a stack overflow.

The array is being allocated from stack and it has size limit. Large objects should be allocated in the heap, through the malloc(). Of course, this complicates things a little. But it’s the only way. There’s a lot you need to learn about memory management before you do what you want.

#include <stdio.h>
#include <stdlib.h>
#define linhas 2000
#define colunas 2000

int main() {
    int * matriz = malloc(linhas * colunas * sizeof(int));
    matriz[0 * linhas + 0] = 0; //coloca um valor na primeira posição da "matriz"
    printf("%d", matriz[0 * linhas + 0]); //claro que neste caso se colocasse apenas 0 funcionaria
    free(matriz);   
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

Read about the difference between arrays and pointers.

I insist there’s a lot to learn about memory management before you go out and do more complex things. If you don’t want to deal with these details, C is not a language for you.

Take advantage and choose a better IDE.

Answer 2

A simple alternative to solve this problem is to allocate the matrix at compile time rather than at runtime on the stack.

int main() {
    static int matriz[2000][2000];
    return 0;
}

This is equivalent to allocating the matrix as a global variable except that the matrix is only visible within the main.