使用valgrind检查内存使用问题

介绍

Valgrind是用于内存检泄漏检测、内存调试以及性能分析的工具集。这里主要介绍其用与内存相关的工具Memcheck，它可以发现大部分的内存问题，例如内存泄漏，使用未初始化内存、内存越界等问题。

安装

我用的时Ubuntu，首先安装Valgrind工具：

 sudo apt-get install valgrind

安装完成后，可以查看是否安装成功：

 valgrind --help

使用

Valgrind使用比较简单：

valgrind --tool=memcheck Path ./excuteFile

注意，在编译为可执行文件时，最好加上-g选项，这样可以看到程序内存问题出现的语句;加上-O0选项，不让编译器给程序做优化。

使用未初始化内存

 #include <iostream>
int main()
{
    int* p;
    *p=10;
    return 0;
}

编译

g++ test1.cpp -g -O0  -o test1

使用Valgrind查看

$ valgrind --tool=memcheck ./test1 
==3978== Memcheck, a memory error detector ==3978== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==3978== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info ==3978== Command: ./test1 ==3978== ==3978== Use of uninitialised value of size 8 ==3978== at 0x4006D5: main (test1.cpp:5) ==3978== ==3978== Invalid write of size 4 ==3978== at 0x4006D5: main (test1.cpp:5) ==3978== Address 0x0 is not stack'd, malloc'd or (recently) free'd ==3978== ==3978== ==3978== Process terminating with default action of signal 11 (SIGSEGV) ==3978== Access not within mapped region at address 0x0 ==3978== at 0x4006D5: main (test1.cpp:5) ==3978== If you believe this happened as a result of a stack ==3978== overflow in your program's main thread (unlikely but ==3978== possible), you can try to increase the size of the ==3978== main thread stack using the --main-stacksize= flag. ==3978== The main thread stack size used in this run was 8388608. ==3978== ==3978== HEAP SUMMARY: ==3978== in use at exit: 0 bytes in 0 blocks ==3978== total heap usage: 0 allocs, 0 frees, 0 bytes allocated ==3978== ==3978== All heap blocks were freed -- no leaks are possible ==3978== ==3978== For counts of detected and suppressed errors, rerun with: -v ==3978== Use --track-origins=yes to see where uninitialised values come from ==3978== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

1、3978是进程ID，最前面那个行是Valgrind的版本信息。
2、后面指出使用未初始化的内存，大小为8,错误发生的位置。
3、最后HEAP SUMMARY说明在HEAP上内存使用情况。
整个输出大概就是以上几个部分。

越界使用内存

#include <iostream>
int main()
{
    int *p=new int[10];
    *(p+10)=1;
    delete[] p;
    return 0;
}

输出：

==4297== Memcheck, a memory error detector ==4297== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==4297== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info ==4297== Command: ./test2 ==4297== ==4297== Invalid write of size 4 ==4297== at 0x40077B: main (test2.cpp:5) ==4297== Address 0x5a1d068 is 0 bytes after a block of size 40 alloc'd ==4297== at 0x4C2B800: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==4297== by 0x40076E: main (test2.cpp:4) ==4297== ==4297== ==4297== HEAP SUMMARY: ==4297== in use at exit: 0 bytes in 0 blocks ==4297== total heap usage: 1 allocs, 1 frees, 40 bytes allocated ==4297== ==4297== All heap blocks were freed -- no leaks are possible ==4297== ==4297== For counts of detected and suppressed errors, rerun with: -v ==4297== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

内存泄漏

#include <iostream>
int main()
{
    int *p=new int[10];
    *(p+1)=1;
    return 0;
}

输出：

==4318== Memcheck, a memory error detector ==4318== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==4318== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info ==4318== Command: ./test3 ==4318== ==4318== ==4318== HEAP SUMMARY: ==4318== in use at exit: 40 bytes in 1 blocks ==4318== total heap usage: 1 allocs, 0 frees, 40 bytes allocated ==4318== ==4318== LEAK SUMMARY: ==4318== definitely lost: 40 bytes in 1 blocks ==4318== indirectly lost: 0 bytes in 0 blocks ==4318== possibly lost: 0 bytes in 0 blocks ==4318== still reachable: 0 bytes in 0 blocks ==4318== suppressed: 0 bytes in 0 blocks ==4318== Rerun with --leak-check=full to see details of leaked memory ==4318== ==4318== For counts of detected and suppressed errors, rerun with: -v ==4318== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

两次释放内存

#include <iostream>
int main()
{
    int *p=new int[10];
    *(p+1)=1;
    delete[] p;
    delete[] p;
    return 0;
}

输出：

==4330== Memcheck, a memory error detector ==4330== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==4330== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info ==4330== Command: ./test4 ==4330== ==4330== Invalid free() / delete / delete[] / realloc() ==4330== at 0x4C2C83C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==4330== by 0x4007A6: main (test4.cpp:7) ==4330== Address 0x5a1d040 is 0 bytes inside a block of size 40 free'd ==4330== at 0x4C2C83C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==4330== by 0x400793: main (test4.cpp:6) ==4330== ==4330== ==4330== HEAP SUMMARY: ==4330== in use at exit: 0 bytes in 0 blocks ==4330== total heap usage: 1 allocs, 2 frees, 40 bytes allocated ==4330== ==4330== All heap blocks were freed -- no leaks are possible ==4330== ==4330== For counts of detected and suppressed errors, rerun with: -v ==4330== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

使用已经释放的内存

#include <iostream>
int main()
{
    int *p=new int[10];
    *(p+1)=1;
    delete[] p;
    *(p+2)=10;
    return 0;
}

输出：

==4341== Memcheck, a memory error detector ==4341== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==4341== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info ==4341== Command: ./test5 ==4341== ==4341== Invalid write of size 4 ==4341== at 0x40079C: main (test5.cpp:7) ==4341== Address 0x5a1d048 is 8 bytes inside a block of size 40 free'd ==4341== at 0x4C2C83C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==4341== by 0x400793: main (test5.cpp:6) ==4341== ==4341== ==4341== HEAP SUMMARY: ==4341== in use at exit: 0 bytes in 0 blocks ==4341== total heap usage: 1 allocs, 1 frees, 40 bytes allocated ==4341== ==4341== All heap blocks were freed -- no leaks are possible ==4341== ==4341== For counts of detected and suppressed errors, rerun with: -v ==4341== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

不匹配使用new/delete或new[]/delete[]

#include <iostream>
int main()
{
    int *p=new int[10];
    *(p+1)=1;
    delete p;
    return 0;
}

输出：

==4375== Memcheck, a memory error detector ==4375== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==4375== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info ==4375== Command: ./test6 ==4375== ==4375== Mismatched free() / delete / delete [] ==4375== at 0x4C2C2BC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==4375== by 0x40078C: main (test6.cpp:6) ==4375== Address 0x5a1d040 is 0 bytes inside a block of size 40 alloc'd ==4375== at 0x4C2B800: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==4375== by 0x40076E: main (test6.cpp:4) ==4375== ==4375== ==4375== HEAP SUMMARY: ==4375== in use at exit: 0 bytes in 0 blocks ==4375== total heap usage: 1 allocs, 1 frees, 40 bytes allocated ==4375== ==4375== All heap blocks were freed -- no leaks are possible ==4375== ==4375== For counts of detected and suppressed errors, rerun with: -v ==4375== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)