4.11  Vérificateur mémoire 2/3

• Vérification de fuite mémoire :

  $ cat -b allocfree.c
       1 #include <stdio.h>
       2 #include <stdlib.h>
       3 #define NB_CHAINES 10
       4 #define MAX_CHAINE 1024
       5 int main(void){
       6 char **tab=malloc(NB_CHAINES*sizeof(char *));
       7 int i;
       8 for(i=0;i<NB_CHAINES;i++){
       9   tab[i]=malloc(MAX_CHAINE*sizeof(char));
      10   sprintf(tab[i],"%d",i);
      11   }
      12 for(i=0;i<NB_CHAINES;i++)
      13   printf("%s\n",tab[i]);
      14 return 0;
  $ valgrind --leak-check=full ./allocfree
  ==5405== Memcheck, a memory error detector
  ...
  ==5405== HEAP SUMMARY:
  ==5405==     in use at exit: 10,280 bytes in 11 blocks
  ==5405==   total heap usage: 11 allocs, 0 frees, 10,280 bytes allocated
  ==5405== 
  ==5405== 10,280 (40 direct, 10,240 indirect) bytes in 1 blocks are definitely lost in loss record 2 of 2
  ==5405==    at 0x4028308: malloc (vg_replace_malloc.c:263)
  ==5405==    by 0x8048491: main (allocfree.c:6)
  ==5405== 
  ==5405== LEAK SUMMARY:
  ==5405==    definitely lost: 40 bytes in 1 blocks
  ==5405==    indirectly lost: 10,240 bytes in 10 blocks
  ==5405==      possibly lost: 0 bytes in 0 blocks
  ==5405==    still reachable: 0 bytes in 0 blocks
  ==5405==         suppressed: 0 bytes in 0 blocks
  ...
  

• Exercice "réparer la fuite mémoire" :
  • ajouter les free nécessaires ;
  • vérifiez avec valgrind que la fuite est réparée.
• Vérification des doubles libérations :

  $ cat -b doublefree.c
       1 #include <stdio.h>
       2 #include <stdlib.h>
       3 int main(void){
       4 int *x=malloc(sizeof(int));
       5 int *y=x;
       6 *x=3;
       7 printf("x=%d y=%d\n",*x,*y);
       8 free(x);
       9 free(y);
      10 return 0;
      11 }
  $ valgrind ./doublefree
  ==3889== Memcheck, a memory error detector
  ...
  ==3889== Invalid free() / delete / delete[] / realloc()
  ==3889==    at 0x402750C: free (vg_replace_malloc.c:427)
  ==3889==    by 0x80484DE: main (doublefree.c:9)
  ==3889==  Address 0x41a8028 is 0 bytes inside a block of size 4 free'd
  ==3889==    at 0x402750C: free (vg_replace_malloc.c:427)
  ==3889==    by 0x80484D2: main (doublefree.c:8)
  ...