C - Segmentation fault in professor's test code

Question

My professor send out test code to run on our program. However, the test code itself has a segmentation fault error on compiling. The error happens on the first printf. However if that line is commented out it just occurs on the next line. It sounds like the code works fine for him, so I'm trying to figure out why it's failing for me. I know he's using C while I'm using C++, but even when I try to compile the test code with gcc instead of g++ it still fails. Anyone know why I might be having problems? Thanks! The code is below.

#include <stdio.h>

main()
{  double A[400000][4],  b[400000], c[4] ;
   double result[4];
   int i, j; double s, t;
   printf("Preparing test: 4 variables, 400000 inequalities\n");
   A[0][0] = 1.0; A[0][1] = 2.0; A[0][2] = 1.0; A[0][3] = 0.0; b[0] = 10000.0;
   A[1][0] = 0.0; A[1][1] = 1.0; A[1][2] = 2.0; A[1][3] = 1.0; b[0] = 10000.0;
   A[2][0] = 1.0; A[2][1] = 0.0; A[2][2] = 1.0; A[2][3] = 3.0; b[0] = 10000.0;
   A[3][0] = 4.0; A[3][1] = 0.0; A[3][2] = 1.0; A[3][3] = 1.0; b[0] = 10000.0;
   c[0]=1.0; c[1]=1.0; c[2]=1.0; c[3]=1.0;
   for( i=4; i< 100000; i++ )
   {  A[i][0] = (12123*i)%104729; 
      A[i][1] = (47*i)%104729; 
      A[i][2] = (2011*i)%104729; 
      A[i][3] = (7919*i)%104729;
      b[i] = A[i][0] + 2*A[i][1] + 3*A[i][2] + 4* A[i][3] + 1 + (i%137);
   }
   A[100000][0] = 0.0; A[100000][1] = 6.0; A[100000][2] = 1.0; 
   A[100000][3] = 1.0; b[100000] = 19.0;
   for( i=100001; i< 200000; i++ )
   {  A[i][0] = (2323*i)%101111; 
      A[i][1] = (74*i)%101111; 
      A[i][2] = (2017*i)%101111; 
      A[i][3] = (7915*i)%101111;
      b[i] = A[i][0] + 2*A[i][1] + 3*A[i][2] + 4* A[i][3] + 2 + (i%89);
   }
   A[200000][0] = 5.0; A[200000][1] = 2.0; A[200000][2] = 0.0; 
   A[200000][3] = 1.0; b[200000] = 11.0;
   for( i=200001; i< 300000; i++ )
   {  A[i][0] = (23123*i)%100003; 
      A[i][1] = (47*i)%100003; 
      A[i][2] = (2011*i)%100003; 
      A[i][3] = (7919*i)%100003;
      b[i] = A[i][0] + 2*A[i][1] + 3*A[i][2] + 4* A[i][3] + 2 + (i%57);
   }
   A[300000][0] = 1.0; A[300000][1] = 2.0; A[300000][2] = 1.0; 
   A[300000][3] = 3.0; b[300000] = 20.0;
   A[300001][0] = 1.0; A[300001][1] = 0.0; A[300001][2] = 5.0; 
   A[300001][3] = 4.0; b[300001] = 32.0;
   A[300002][0] = 7.0; A[300002][1] = 1.0; A[300002][2] = 1.0; 
   A[300002][3] = 7.0; b[300002] = 40.0;
   for( i=300003; i< 400000; i++ )
   {  A[i][0] = (13*i)%103087; 
      A[i][1] = (99*i)%103087; 
      A[i][2] = (2012*i)%103087; 
      A[i][3] = (666*i)%103087;
      b[i] = A[i][0] + 2*A[i][1] + 3*A[i][2] + 4* A[i][3] + 1;
   }

   printf("Running test: 400000 inequalities, 4 variables\n");
   //j = rand_lp(40, &(A[0][0]), &(b[0]), &(c[0]), &(result[0]));
   printf("Test: extremal point (%f, %f, %f, %f) after %d recomputation steps\n", 
          result[0], result[1], result[2], result[3], j);
   printf("Answer should be (1,2,3,4)\n End Test\n");
}

Answer 1

Try to change:

double A[400000][4],  b[400000], c[4] ;

to

static double A[400000][4],  b[400000], c[4] ;

Your declaration of the A array has automatic storage duration which probably means on your system it is stored on the stack. Your total stack for your process is likely to be lower than that and you encountered a stack overflow.

On Linux, you can run the ulimit command:

$ ulimit -s
8192
$

to see the stack size in kB allocated for a process. For example, 8192 kB on my machine.

Answer 2

You have overflowed the limits of the stack. Your prof declares 15MB of data in main's stack frame. That's just too big.

Since the lifetime of an ojbect declared at the top of main is essentially the entire program, just declare the objects as static. That way they'll be in the (relatively limitless) data segment, and have nearly the same lifetime.

Try changing this line:

double A[400000][4],  b[400000], c[4] ;

to this:

static double A[400000][4],  b[400000], c[4] ;