实例介绍利用valgrind定位内存异常释放问题（double free 和wrong free）

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         之前介绍过利用valgrind来定位内存泄漏（慢性病， 会导致程序在某个不确定的时刻异常）， 本文我们来简要介绍利用valgrind来定位内存的重复释放（急性病， 会报纸程序崩溃）。 看程序：

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>int main()
{char *p = (char *)malloc(30);free(p);free(p);return 0;
}

       我们用valgrind来检测一下：

[root@xxx ~/valgrind-3.8.1/bin]# g++ -g test.cpp
[root@xxx ~/valgrind-3.8.1/bin]# 
[root@xxx ~/valgrind-3.8.1/bin]# ./valgrind --tool=memcheck --leak-check=yes --show-reachable=yes ./a.out
==18229== Memcheck, a memory error detector
==18229== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==18229== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==18229== Command: ./a.out
==18229== 
==18229== Invalid free() / delete / delete[] / realloc()
==18229==    at 0x4C27300: free (vg_replace_malloc.c:446)
==18229==    by 0x400611: main (test.cpp:9)
==18229==  Address 0x5d84040 is 0 bytes inside a block of size 30 free'd
==18229==    at 0x4C27300: free (vg_replace_malloc.c:446)
==18229==    by 0x400605: main (test.cpp:8)
==18229== 
==18229== 
==18229== HEAP SUMMARY:
==18229==     in use at exit: 0 bytes in 0 blocks
==18229==   total heap usage: 1 allocs, 2 frees, 30 bytes allocated
==18229== 
==18229== All heap blocks were freed

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