Valgrind montrant une fuite de mémoire pour les blocs printf et inutilisés

#include  #include  #include  int main(int argc, char *argv[]){ char *str = malloc(sizeof(char)*5); str = strcpy(str, "test"); printf("%s\n", str); free(str); return 0; } 

Lorsque j’utilise Valgrind sur mon Mac (OS X, 10.9.5), le message suivant s’affiche:

 ==77215== HEAP SUMMARY: ==77215== in use at exit: 29,211 bytes in 374 blocks ==77215== total heap usage: 451 allocs, 77 frees, 35,160 bytes allocated ==77215== ==77215== 4,096 bytes in 1 blocks are still reachable in loss record 76 of 76 ==77215== at 0x66CB: malloc (in /usr/local/Cellar/valgrind/3.10.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so) ==77215== by 0x182855: __smakebuf (in /usr/lib/system/libsystem_c.dylib) ==77215== by 0x197217: __swsetup (in /usr/lib/system/libsystem_c.dylib) ==77215== by 0x1B0158: __v2printf (in /usr/lib/system/libsystem_c.dylib) ==77215== by 0x1B06AF: __xvprintf (in /usr/lib/system/libsystem_c.dylib) ==77215== by 0x187B29: vfprintf_l (in /usr/lib/system/libsystem_c.dylib) ==77215== by 0x18596F: printf (in /usr/lib/system/libsystem_c.dylib) ==77215== by 0x100000F2B: main (test.c:8) ==77215== ==77215== LEAK SUMMARY: ==77215== definitely lost: 0 bytes in 0 blocks ==77215== indirectly lost: 0 bytes in 0 blocks ==77215== possibly lost: 0 bytes in 0 blocks ==77215== still reachable: 4,096 bytes in 1 blocks ==77215== suppressed: 25,115 bytes in 373 blocks ==77215== ==77215== For counts of detected and suppressed errors, rerun with: -v ==77215== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 15 from 15) 

printf alloue-t-il de la mémoire par lui-même? Si je retire l’ printf je ne reçois que les éléments suivants:

 ==77237== HEAP SUMMARY: ==77237== in use at exit: 25,115 bytes in 373 blocks ==77237== total heap usage: 450 allocs, 77 frees, 31,064 bytes allocated ==77237== ==77237== LEAK SUMMARY: ==77237== definitely lost: 0 bytes in 0 blocks ==77237== indirectly lost: 0 bytes in 0 blocks ==77237== possibly lost: 0 bytes in 0 blocks ==77237== still reachable: 0 bytes in 0 blocks ==77237== suppressed: 25,115 bytes in 373 blocks ==77237== ==77237== For counts of detected and suppressed errors, rerun with: -v ==77237== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 15 from 15) 

D’où viennent les 373 blocs?

Tant que l’équipe Valgrind ne donne pas la priorité à OS X, vous pouvez sans risque supposer qu’elle ne donnera pas des résultats corrects sur les systèmes Apple exécutant des versions d’OS X inférieures à 10.7.

Sur mon ordinateur Mavericks (10.9.5), l’avertissement suivant de Valgrind (3.9.0) est toujours affiché.

 WARNING: Support on MacOS 10.8/10.9 is experimental and mostly broken. WARNING: Expect incorrect results, assertions and crashes. WARNING: In particular, Memcheck on 32-bit programs will fail to WARNING: detect any errors associated with heap-allocated data. 

Pour ce que ça vaut, Valgrind 3.10.0 ne montre aucune fuite sur mon installation de Debian Jessie.

Cela ne vous dit pas qu’il y a une fuite:

 ==77215== LEAK SUMMARY: ==77215== definitely lost: 0 bytes in 0 blocks ==77215== indirectly lost: 0 bytes in 0 blocks ==77215== possibly lost: 0 bytes in 0 blocks ==77215== still reachable: 4,096 bytes in 1 blocks ==77215== suppressed: 25,115 bytes in 373 blocks 

cela vous dit qu’il y a un bloc qui est toujours accessible; La présence ou non d’une fuite dépend de votre définition de «fuite». Cela signifie qu’il existe un pointeur vers le bloc quelque part.

Référez-vous à la fuite toujours joignable détectée par Valgrind pour plus d’informations.