内存问题排查工具 --- valgrind

 1: int main()
 2: {
 3:     char *p = malloc(sizeof(char) * 10);
 4:     if (p == NULL) {
 5:         return 0;
 6:     }
 7: 
 8:     *p++ = ‘a‘;
 9:     *p++ = ‘b‘;
10: 
11:     printf("%s\n", *p);
12: 
13:     return 0;
14: }

1: gcc -g -o core1 core1.c

1: valgrind --leak-check=yes --show-reachable=yes ./core

 1: ==25500== Memcheck, a memory error detector
 2: ==25500== Copyright (C) 2002-2009, and GNU GPL‘d, by Julian Seward et al.
 3: ==25500== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
 4: ==25500== Command: ./core1
 5: ==25500==
 6: ==25500== Conditional jump or move depends on uninitialised value(s)
 7: ==25500==    at 0x36A104546A: vfprintf (in /lib64/libc-2.12.so)
 8: ==25500==    by 0x36A104EAC9: printf (in /lib64/libc-2.12.so)
 9: ==25500==    by 0x40055D: main (core1.c:13)
10: ==25500==
11: (null)
12: ==25500==
13: ==25500== HEAP SUMMARY:
14: ==25500==     in use at exit: 10 bytes in 1 blocks
15: ==25500==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
16: ==25500==
17: ==25500== 10 bytes in 1 blocks are definitely lost in loss record 1 of 1
18: ==25500==    at 0x4A0515D: malloc (vg_replace_malloc.c:195)
19: ==25500==    by 0x400515: main (core1.c:5)
20: ==25500==
21: ==25500== LEAK SUMMARY:
22: ==25500==    definitely lost: 10 bytes in 1 blocks
23: ==25500==    indirectly lost: 0 bytes in 0 blocks
24: ==25500==      possibly lost: 0 bytes in 0 blocks
25: ==25500==    still reachable: 0 bytes in 0 blocks
26: ==25500==         suppressed: 0 bytes in 0 blocks
27: ==25500==
28: ==25500== For counts of detected and suppressed errors, rerun with: -v
29: ==25500== Use --track-origins=yes to see where uninitialised values come from
30: ==25500== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 6 from 6)

 1: struct elem {
 2:     int     a;
 3:     double  b;
 4: };
 5: 
 6: int main()
 7: {
 8:     struct elem *e = malloc(sizeof(struct elem));
 9:     if (e == NULL) {
10:         return 0;
11:     }
12: 
13:     e->a = 10;
14:     e->b = 10.10;
15: 
16:     double *xx = &e->b;
17: 
18:     printf("%f\n", *xx);
19: 
20:     free(e);
21: 
22:     printf("%f\n", *xx);
23: 
24:     return 0;
25: }

 1: [cobbliu@MacBook]$ valgrind --leak-check=yes --show-reachable=yes ./core2
 2: ==26148== Memcheck, a memory error detector
 3: ==26148== Copyright (C) 2002-2009, and GNU GPL‘d, by Julian Seward et al.
 4: ==26148== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
 5: ==26148== Command: ./core2
 6: ==26148==
 7: 10.100000
 8: ==26148== Invalid read of size 8
 9: ==26148==    at 0x4005CA: main (core2.c:26)
10: ==26148==  Address 0x502a048 is 8 bytes inside a block of size 16 free‘d
11: ==26148==    at 0x4A04D72: free (vg_replace_malloc.c:325)
12: ==26148==    by 0x4005C5: main (core2.c:24)
13: ==26148==
14: 10.100000
15: ==26148==
16: ==26148== HEAP SUMMARY:
17: ==26148==     in use at exit: 0 bytes in 0 blocks
18: ==26148==   total heap usage: 1 allocs, 1 frees, 16 bytes allocated
19: ==26148==
20: ==26148== All heap blocks were freed -- no leaks are possible
21: ==26148==
22: ==26148== For counts of detected and suppressed errors, rerun with: -v
23: ==26148== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 6)

 1: int main()
 2: {
 3:     char *p = malloc(sizeof(char) * 10);
 4:     if (p == NULL) {
 5:         return 0;
 6:     }
 7: 
 8:     char *q = p;
 9: 
10:     *p++ = ‘a‘;
11:     *p++ = ‘b‘;
12: 
13:     printf("%s\n", *p);
14: 
15:     free(p);
16:     free(q);
17:     return 0;
18: }

 1: [cobbliu@MacBook]$ valgrind --leak-check=yes --show-reachable=yes ./core1
 2: ==26874== Memcheck, a memory error detector
 3: ==26874== Copyright (C) 2002-2009, and GNU GPL‘d, by Julian Seward et al.
 4: ==26874== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
 5: ==26874== Command: ./core1
 6: ==26874==
 7: ==26874== Conditional jump or move depends on uninitialised value(s)
 8: ==26874==    at 0x36A104546A: vfprintf (in /lib64/libc-2.12.so)
 9: ==26874==    by 0x36A104EAC9: printf (in /lib64/libc-2.12.so)
10: ==26874==    by 0x4005B5: main (core1.c:15)
11: ==26874==
12: (null)
13: ==26874== Invalid free() / delete / delete[]
14: ==26874==    at 0x4A04D72: free (vg_replace_malloc.c:325)
15: ==26874==    by 0x4005C1: main (core1.c:17)
16: ==26874==  Address 0x502a042 is 2 bytes inside a block of size 10 alloc‘d
17: ==26874==    at 0x4A0515D: malloc (vg_replace_malloc.c:195)
18: ==26874==    by 0x400565: main (core1.c:5)
19: ==26874==
20: ==26874==
21: ==26874== HEAP SUMMARY:
22: ==26874==     in use at exit: 0 bytes in 0 blocks
23: ==26874==   total heap usage: 1 allocs, 2 frees, 10 bytes allocated
24: ==26874==
25: ==26874== All heap blocks were freed -- no leaks are possible
26: ==26874==
27: ==26874== For counts of detected and suppressed errors, rerun with: -v
28: ==26874== Use --track-origins=yes to see where uninitialised values come from
29: ==26874== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 6 from 6)