Valgrind 是一款 Linux下（支持 x86、x86_64和ppc32）程序的内存调试工具，它可以对编译后的二进制程序进行内存使用监测（C语言中的malloc和free，以及C++中的new和delete），找出内存泄漏问题。
Valgrind 中包含的 Memcheck 工具可以检查以下的程序错误：
使用未初始化的内存 (Use of uninitialised memory)
使用已经释放了的内存 (Reading/writing memory after it has been free’d)
使用超过malloc分配的内存空间(Reading/writing off the end of malloc’d blocks)
对堆栈的非法访问 (Reading/writing inappropriate areas on the stack)
申请的空间是否有释放 (Memory leaks – where pointers to malloc’d blocks are lost forever)
malloc/free/new/delete申请和释放内存的匹配(Mismatched use of malloc/new/new [] vs free/delete/delete [])
src和dst的重叠(Overlapping src and dst pointers in memcpy() and related functions)
重复free
1、编译安装 Valgrind：
wget http://valgrind.org/downloads/valgrind-3.4.1.tar.bz2 tar xvf valgrind-3.4.1.tar.bz2 cd valgrind-3.4.1/ ./configure --prefix=/usr/local/webserver/valgrind make make install
2、使用示例：对“ls”程序进程检查，返回结果中的“definitely lost: 0 bytes in 0 blocks.”表示没有内存泄漏。
[root@xoyo42 /]#/usr/local/webserver/valgrind/bin/valgrind --tool=memcheck --leak-check=full ls / ==1157== Memcheck, a memory error detector. ==1157== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al. ==1157== Using LibVEX rev 1884, a library for dynamic binary translation. ==1157== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP. ==1157== Using valgrind-3.4.1, a dynamic binary instrumentation framework. ==1157== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al. ==1157== For more details, rerun with: -v ==1157== bin data0 dev home lib64 media mnt opt root selinux sys tcsql.db.idx.pkey.dec ttserver.pid var boot data1 etc lib lost+found misc net proc sbin srv tcsql.db tmp usr ==1157== ==1157== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 5 from 1) ==1157== malloc/free: in use at exit: 28,471 bytes in 36 blocks. ==1157== malloc/free: 166 allocs, 130 frees, 51,377 bytes allocated. ==1157== For counts of detected errors, rerun with: -v ==1157== searching for pointers to 36 not-freed blocks. ==1157== checked 174,640 bytes. ==1157== ==1157== LEAK SUMMARY: ==1157== definitely lost: 0 bytes in 0 blocks. ==1157== possibly lost: 0 bytes in 0 blocks. ==1157== still reachable: 28,471 bytes in 36 blocks. ==1157== suppressed: 0 bytes in 0 blocks. ==1157== Reachable blocks (those to which a pointer was found) are not shown. ==1157== To see them, rerun with: --leak-check=full --show-reachable=yes
3、使用示例：对一个使用libevent库编写的“httptest”程序进程检查，返回结果中的“definitely lost: 255 bytes in 5 blocks.”表示发生内存泄漏。
[root@xoyo42 tcsql-0.1]# /usr/local/webserver/valgrind/bin/valgrind --tool=memcheck --leak-check=full ./httptest ==1274== Memcheck, a memory error detector. ==1274== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al. ==1274== Using LibVEX rev 1884, a library for dynamic binary translation. ==1274== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP. ==1274== Using valgrind-3.4.1, a dynamic binary instrumentation framework. ==1274== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al. ==1274== For more details, rerun with: -v ==1274== ==1274== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1005 from 2) ==1274== malloc/free: in use at exit: 402,291 bytes in 74 blocks. ==1274== malloc/free: 15,939 allocs, 15,865 frees, 6,281,523 bytes allocated. ==1274== For counts of detected errors, rerun with: -v ==1274== searching for pointers to 74 not-freed blocks. ==1274== checked 682,468,160 bytes. ==1274== ==1274== 255 bytes in 5 blocks are definitely lost in loss record 17 of 32 ==1274== at 0x4A05FBB: malloc (vg_replace_malloc.c:207) ==1274== by 0x3C1D809BC6: evhttp_decode_uri (http.c:2105) ==1274== by 0x401C75: tcsql_handler (in /data0/tcsql/cankao/tcsql-0.1/tcsql) ==1274== by 0x3C1D80C88F: evhttp_get_body (http.c:1582) ==1274== by 0x3C1D8065F7: event_base_loop (event.c:392) ==1274== by 0x403E2F: main (in /data0/tcsql/cankao/tcsql-0.1/tcsql) ==1274== ==1274== LEAK SUMMARY: ==1274== definitely lost: 255 bytes in 5 blocks. ==1274== possibly lost: 0 bytes in 0 blocks. ==1274== still reachable: 402,036 bytes in 69 blocks. ==1274== suppressed: 0 bytes in 0 blocks. ==1274== Reachable blocks (those to which a pointer was found) are not shown. ==1274== To see them, rerun with: --leak-check=full --show-reachable=yes
检查httptest程序，发现有一处“char *decode_uri = evhttp_decode_uri(evhttp_request_uri(req));”中的“decode_uri”没有被free，再程序处理完成后加上“free(decode_uri);”后，再使用Valgrind检查，结果已经是“definitely lost: 0 bytes in 0 blocks.”。
