c - 免费 : Invalid Size : Valgrind

Question

我想使用 valgrind 释放一个 malloc:

我收到这个错误:

MCM : 1900
free(): invalid size
Abandon (core dumped)

这是我编译的代码:

char test[6][10] = {"MCM", "MCML", "MCMLXXXV", "MCMXC", "MM", "MMVI"};
 int size[] = {3, 4, 8, 5, 2, 4}; 

 for (int i = 0; i < 6; i++)
 {   
     char *a = malloc(sizeof(char) * size[i]);
     a = test[i];
     int result = convert(a, roman, arabe, size[i]);
     printf("%s : %d\n",a ,result);
     free(a);
 }   

并通过使用:

valgrind --leak-check=full ./roman

我收到这条消息:

==23809== Memcheck, a memory error detector
==23809== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==23809== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==23809== Command: ./roman
==23809== 
MCM : 1900
==23809== Invalid free() / delete / delete[] / realloc()
==23809==    at 0x4C30D3B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==23809==    by 0x108B45: main (roman.c:76)
==23809==  Address 0x1fff0003d0 is on thread 1's stack
==23809==  in frame #1, created by main (roman.c:47)
==23809== 
MCML : 1950
MCMLXXXV : 1985
MCMXC : 1990
MM : 2000
MMVI : 2006
MCM      = 1900
MCML     = 1950
MCMLXXXV = 1985
MCMXC    = 1990
MM       = 2000
MMVI     = 2006
==23809== 
==23809== HEAP SUMMARY:
==23809==     in use at exit: 26 bytes in 6 blocks
==23809==   total heap usage: 7 allocs, 7 frees, 1,050 bytes allocated
==23809== 
==23809== 26 bytes in 6 blocks are definitely lost in loss record 1 of 1
==23809==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==23809==    by 0x108ABE: main (roman.c:72)
==23809== 
==23809== LEAK SUMMARY:
==23809==    definitely lost: 26 bytes in 6 blocks
==23809==    indirectly lost: 0 bytes in 0 blocks
==23809==      possibly lost: 0 bytes in 0 blocks
==23809==    still reachable: 0 bytes in 0 blocks
==23809==         suppressed: 0 bytes in 0 blocks
==23809== 
==23809== For counts of detected and suppressed errors, rerun with: -v
==23809== ERROR SUMMARY: 7 errors from 2 contexts (suppressed: 0 from 0)

据我所知，有四个部分:

==23809== Invalid free() / delete / delete[] / realloc()
==23809==    at 0x4C30D3B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==23809==    by 0x108B45: main (roman.c:76)
==23809==  Address 0x1fff0003d0 is on thread 1's stack
==23809==  in frame #1, created by main (roman.c:47)
==23809== 

我看到我的错误是第 76 行:

free(a)

我不知道怎么解决。

而且我不太了解 HEAP SUMMARY 和 LEAK SUMMARY:它对应什么？堆总结:

==23809== HEAP SUMMARY:
==23809==     in use at exit: 26 bytes in 6 blocks 
==23809==   total heap usage: 7 allocs, 7 frees, 1,050 bytes allocated
==23809== 
==23809== 26 bytes in 6 blocks are definitely lost in loss record 1 of 1
==23809==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==23809==    by 0x108ABE: main (roman.c:72)

泄漏摘要:

==23809== LEAK SUMMARY:
==23809==    definitely lost: 26 bytes in 6 blocks
==23809==    indirectly lost: 0 bytes in 0 blocks
==23809==      possibly lost: 0 bytes in 0 blocks
==23809==    still reachable: 0 bytes in 0 blocks
==23809==         suppressed: 0 bytes in 0 blocks

结论:

==23809== For counts of detected and suppressed errors, rerun with: -v
==23809== ERROR SUMMARY: 7 errors from 2 contexts (suppressed: 0 from 0)

有人可以解释这四个部分吗？

Answer 1

你似乎认为:

 a = test[i];

将字符串复制到a 指向的内存中。但实际上它只是丢弃了存储在a 中的指针，并将其替换为指向test 的指针。所以你已经丢失(泄漏)了你分配的内存，因此 freeing 它是一个错误。