[Nauty-list] Segmentation fault with readg()

[Tristan Miller]

Greetings.

In 2011, a subscriber to this list asked how to read in the graphs produced 
by geng.  William Rummler's answer 
<http://dcsmail.anu.edu.au/pipermail/nauty-list/2011-January/000582.html> 
advised the subscriber to use the opengraphfile() and readg() functions 
from gtools.h; I quote the example code below.  I tried compiling and 
running this code but the output doesn't seem to correspond to the given 
graph, and moreover it seems it always crashes with a segmentation fault on 
the second call to readg():


$ gcc -o readgraph readgraph.c nauty.a
$ geng 3 1:0 | ./readgraph
 0 0 0
 0 0 0
 0 0 0

Segmentation fault


Is there some bug in the example (or in nauty itself), or am I doing 
something wrong?


Here's the example code originally posted by William Rummler:

#define MAXN 30
#include "gtools.h"

int
main( void )
{
  /*
   * Variables for using with opengraphfile() and readg()
   */
  FILE *f;
  graph g[ MAXN * MAXM ];
  int codetype, m, n;

  /*
   * Example:
   * Reading graphs from standard input and printing their adjacency 
matrices
   */
  set *v;
  int i, j;
  f = opengraphfile( NULL, &codetype, 0, 0 );
  while( readg( f, g, 0, &m, &n ) )
    {
      for ( i = 0; i < n; ++i )
        {
          v = GRAPHROW( g, i, m );
          for ( j = 0; j < n; ++j )
            {
              printf( " %d", ISELEMENT( v, j ) ? 1 : 0 );
            }
          printf( "\n" );
        }
      printf( "\n" );
    }
  return 0;
}

Regards,
Tristan

-- 
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