Question

Another student asked me what could be wrong with his C code. I successfully reproduced the erroneous behavior and have completely no idea why this segfaults. Consider this tiny C programm:

#include <stdio.h>

int main(void) {
    int N = 590;
    double A[N][N];
    double B[N][N];
    double C[N][N];
    printf("done");
}

• Set N to a value <= 590:
  This runs without errors, with or without output.
• set N to a value > 590:
  • Runs flawlessy with output line removed.
  • Compile and run with output: segmentation fault

What’s the reason for this? Can anybody explain?

Answer 1

You try to allocate more memory than it’s available on the stack which causes stack overflow. Usually it is much better to allocate huge arrays like that dynamically by using malloc, calloc or realloc. Don’t forget to free this memory by calling free when you finish with it 🙂

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