bug_datasize.c

The bug we address here is one encountered when (unfortunately) declaring a variable named datasize. Here is an small example.

Let’s just include some simple 1D headers.

#include "grid/multigrid1D.h"
#include "run.h"

We only put 4 points but this bug appears for more values of N, and in 2D as well.

int main()
{
  N = 4;
  run();  
}

We setup a simple init event where we declare a variable named datasize as an integer and a scalar named toto.

event init (i = 0) {
  int datasize = 7;
  scalar toto[];

We fill toto with random values and display them in the same loop.

  printf ("Value of toto in the first loop :\n");
  foreach() {
    toto[] = noise();
    printf("%g ", toto[]);
  }

We display toto again, in another loop.

  printf ("\nValue of toto in the second loop :\n");
  foreach()
    printf("%g ", toto[]);
}

We make it so the programm ends after only one time step, no need to go further to see the bug.

event end (t = 0.00001) {
  printf ("\n");
}

We get the following results :

Value of toto in the first loop : -0.680375 0.211234 -0.566198 -0.59688

Value of toto in the second loop : 6.92254e+235 -3.03422e-189 1.26266e+43 -0.59688

The problem here is that when compiling (even with the -Wall -Wextra options), no error or warning is raised.

Important note : This bug arises only when datasize < 8.