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)