valgrind检查内存泄露

c++没有垃圾回收机制，程序往往会出现内存泄露，即从堆上获取资源（malloc/new）、用完后没有返回（free/delete）给系统。
valgrind是一个检测内存泄露的工具。

安装

sudo apt-get install valgrind

使用

写一个产生内存泄露的代码，名为leak1.cpp

//leak1.cpp
#include 
using namespace std;
int main()
{
  char* p = (char*)malloc(4);
  //no free
  return 0;
}

编译、输出名为leak的可执行程序：

g++ -g leak.cpp -o leak1

注意这里需要使用debug模式，即加-g，否则一会儿valgrind没法输出错误的地方。
然后就是valgrind：

valgrind --tool=memcheck --leak-check=yes ./leak1

这里valgrind的参数有：--tool=memcheck和--leak-check=yes，而./leak1是我的可执行程序。
输出类似如下：

==15133== Memcheck, a memory error detector
==15133== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==15133== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==15133== Command: ./leak
==15133== 
==15133== 
==15133== HEAP SUMMARY:
==15133==     in use at exit: 4 bytes in 1 blocks
==15133==   total heap usage: 1 allocs, 0 frees, 4 bytes allocated
==15133== 
==15133== 4 bytes in 1 blocks are definitely lost in loss record 1 of 1
==15133==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==15133==    by 0x400537: main (leak.cpp:4)
==15133== 
==15133== LEAK SUMMARY:
==15133==    definitely lost: 4 bytes in 1 blocks
==15133==    indirectly lost: 0 bytes in 0 blocks
==15133==      possibly lost: 0 bytes in 0 blocks
==15133==    still reachable: 0 bytes in 0 blocks
==15133==         suppressed: 0 bytes in 0 blocks
==15133== 
==15133== For counts of detected and suppressed errors, rerun with: -v
==15133== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

可以看到内存泄露发生在源码的第4行。