#include <stdlib.h>
                                                                                
int main() {

  int *t = (int *)malloc(10);
                                                                                
  free(t);
  free(t);
                                                                                
}

Example output:

[ 26 ] 9.13-15 -: setenv MALLOC_CHECK_ 1
[ 27 ] 9.13-15 -: ./test
malloc: using debugging hooks
free(): invalid pointer 0x8049560!