linux c 內存泄露檢測工具：valgrind
Linux c/c++上常用內存泄露檢測工具有valgrind, Rational purify。Valgrind免費。Valgrind 可以在 32 位或 64 位 PowerPC/Linux 內核上工作。
Valgrind工具包包含多個工具，如Memcheck,Cachegrind,Helgrind, Callgrind，Massif。下面分別介紹個工具的作用：
Memcheck 工具主要檢查下面的程序錯誤：
? 使用未初始化的內存 (Use of uninitialised memory)
? 使用已經釋放了的內存 (Reading/writing memory after it has been free’d)
? 使用超過 malloc分配的內存空間(Reading/writing off the end of malloc’d blocks)
? 對堆棧的非法訪問 (Reading/writing inappropriate areas on the stack)
? 申請的空間是否有釋放 (Memory leaks – where pointers to malloc’d blocks are lost forever)
? malloc/free/new/delete申請和釋放內存的匹配(Mismatched use of malloc/new/new [] vs free/delete/delete [])
? src和dst的重疊(Overlapping src and dst pointers in memcpy() and related functions)
Valgrind不檢查靜態分配數組的使用情況。
Valgrind占用了更多的內存--可達兩倍于你程序的正常使用量。如果你用Valgrind來檢測使用大量內存的程序就會遇到問題，它可能會用很長的時間來運行測試
2.1. 下載安裝
http://www.valgrind.org
安裝
./configure;make;make install
2.2. 編譯程序
被檢測程序加入 –g -fno-inline 編譯選項保留調試信息。
2.3. 內存泄露檢測
$ valgrind --tool=memcheck --log-file=/home/trunk/valgrind_log_all --leak-check=full --error-limit=no --show-leak-kinds=all /opt/lim/bin/limserver
其中--leak-check=full 指的是完全檢查內存泄漏，--show-reachable=yes是顯示內存泄漏的地點，--trace-children=yes是跟入子進程。當程序正常退出的時候valgrind自然會輸出內存泄漏的信息。
1.內存泄露：
#include <stdio.h>void function()
{ int *p = (int*)malloc(10*sizeof(int)); p[10] = 0;
}int main()
{ function(); return 0;
} 相關日志：
==20220== Memcheck, a memory error detector
==20220== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==20220== Using Valgrind-3.6.1-Debian and LibVEX; rerun with -h for copyright info
==20220== Command: ./test
==20220== Parent PID: 20160
==20220==
==20220== Invalid write of size 4
==20220== at 0x80483FF: function (in /mnt/Documents/Training/valgrind/test)
==20220== by 0x8048411: main (in /mnt/Documents/Training/valgrind/test)
==20220== Address 0x41be050 is 0 bytes after a block of size 40 alloc'd
==20220== at 0x4028876: malloc (vg_replace_malloc.c:236)
==20220== by 0x80483F5: function (in /mnt/Documents/Training/valgrind/test)
==20220== by 0x8048411: main (in /mnt/Documents/Training/valgrind/test)
==20220==
==20220==
==20220== HEAP SUMMARY:
==20220== in use at exit: 40 bytes in 1 blocks
==20220== total heap usage: 1 allocs, 0 frees, 40 bytes allocated
==20220==
==20220== LEAK SUMMARY:
==20220== definitely lost: 40 bytes in 1 blocks
==20220== indirectly lost: 0 bytes in 0 blocks
==20220== possibly lost: 0 bytes in 0 blocks
==20220== still reachable: 0 bytes in 0 blocks
==20220== suppressed: 0 bytes in 0 blocks
==20220== Rerun with --leak-check=full to see details of leaked memory
==20220==
==20220== For counts of detected and suppressed errors, rerun with: -v
==20220== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 11 from 6)
2.使用未初始化的內存
#include <stdio.h>int main()
{ int a; if (a==1)
{ printf("a==%d\n",a);
} return 0;
} 日志分析：
==20345== Memcheck, a memory error detector
==20345== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==20345== Using Valgrind-3.6.1-Debian and LibVEX; rerun with -h for copyright info
==20345== Command: ./test
==20345==
==20345== Conditional jump or move depends on uninitialised value(s)
==20345== at 0x80483F2: main (in /mnt/Documents/Training/valgrind/test)
==20345==
==20345==
==20345== HEAP SUMMARY:
==20345== in use at exit: 0 bytes in 0 blocks
==20345== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==20345==
==20345== All heap blocks were freed -- no leaks are possible
==20345==
==20345== For counts of detected and suppressed errors, rerun with: -v
==20345== Use --track-origins=yes to see where uninitialised values come from
==20345== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 11 from 6)
可以使用--track-origins=yes 得到更多的信息
3.內存讀寫越界
#include <stdio.h>int main()
{ int *a = (int*)malloc(5*sizeof(int)); a[5] = 1; return 0;
} ==20368== Memcheck, a memory error detector
==20368== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==20368== Using Valgrind-3.6.1-Debian and LibVEX; rerun with -h for copyright info
==20368== Command: ./test
==20368==
==20368== Invalid write of size 4
==20368== at 0x8048404: main (in /mnt/Documents/Training/valgrind/test)
==20368== Address 0x41be03c is 0 bytes after a block of size 20 alloc'd
==20368== at 0x4028876: malloc (vg_replace_malloc.c:236)
==20368== by 0x80483F8: main (in /mnt/Documents/Training/valgrind/test)
==20368==
==20368==
==20368== HEAP SUMMARY:
==20368== in use at exit: 20 bytes in 1 blocks
==20368== total heap usage: 1 allocs, 0 frees, 20 bytes allocated
==20368==
==20368== LEAK SUMMARY:
==20368== definitely lost: 20 bytes in 1 blocks
==20368== indirectly lost: 0 bytes in 0 blocks
==20368== possibly lost: 0 bytes in 0 blocks
==20368== still reachable: 0 bytes in 0 blocks
==20368== suppressed: 0 bytes in 0 blocks
==20368== Rerun with --leak-check=full to see details of leaked memory
==20368==
==20368== For counts of detected and suppressed errors, rerun with: -v
==20368== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 11 from 6)
4.內存申請釋放管理錯誤
#include <stdio.h>int main()
{ int *a = new int[5]; /*free(a);*/ delete a; return 0;
} ==20387== Memcheck, a memory error detector
==20387== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==20387== Using Valgrind-3.6.1-Debian and LibVEX; rerun with -h for copyright info
==20387== Command: ./test
==20387==
==20387== Mismatched free() / delete / delete []
==20387== at 0x4027919: operator delete(void*) (vg_replace_malloc.c:387)
==20387== by 0x8048498: main (in /mnt/Documents/Training/valgrind/test)
==20387== Address 0x42f2028 is 0 bytes inside a block of size 20 alloc'd
==20387== at 0x4027F65: operator new[](unsigned int) (vg_replace_malloc.c:299)
==20387== by 0x8048488: main (in /mnt/Documents/Training/valgrind/test)
==20387==
==20387==
==20387== HEAP SUMMARY:
==20387== in use at exit: 0 bytes in 0 blocks
==20387== total heap usage: 1 allocs, 1 frees, 20 bytes allocated
==20387==
==20387== All heap blocks were freed -- no leaks are possible
==20387==
==20387== For counts of detected and suppressed errors, rerun with: -v
==20387== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 17 from 6)
內存泄露
問題描述：
內存泄露（Memory leak）指的是，在程序中動態申請的內存，在使用完后既沒有釋放，又無法被程序的其他部分訪問。內存泄露是在開發大型程序中最令人頭疼的問題，以至于有 人說，內存泄露是無法避免的。其實不然，防止內存泄露要從良好的編程習慣做起，另外重要的一點就是要加強單元測試（Unit Test），而memcheck就是這樣一款優秀的工具。
下面是一個比較典型的內存泄露案例。main函數調用了mk函數生成樹結點，可是在調用完成之后，卻沒有相應的函數：nodefr釋放內存，這樣內存中的這個樹結構就無法被其他部分訪問，造成了內存泄露。
在一個單獨的函數中，每個人的內存泄露意識都是比較強的。但很多情況下，我們都會對malloc/free 或new/delete做一些包裝，以符合我們特定的需要，無法做到在一個函數中既使用又釋放。這個例子也說明了內存泄露最容易發生的地方：即兩個部分的 接口部分，一個函數申請內存，一個函數釋放內存。并且這些函數由不同的人開發、使用，這樣造成內存泄露的可能性就比較大了。這需要養成良好的單元測試習 慣，將內存泄露消滅在初始階段。
清單 11
清單 11.2
清單 11.3
結果分析：
假設上述文件名位tree.h, tree.cpp, badleak.cpp，生成的可執行程序為badleak，用memcheck對其進行測試，輸出如下。
清單 12
該示例程序是生成一棵樹的過程，每個樹節點的大小為12（考慮內存對齊），共8個節點。從上述輸出可以看出，所有的內存泄露都被發現。 Memcheck將內存泄露分為兩種，一種是可能的內存泄露（Possibly lost），另外一種是確定的內存泄露（Definitely lost）。Possibly lost 是指仍然存在某個指針能夠訪問某塊內存，但該指針指向的已經不是該內存首地址。Definitely lost 是指已經不能夠訪問這塊內存。而Definitely lost又分為兩種：直接的（direct）和間接的（indirect）。直接和間接的區別就是，直接是沒有任何指針指向該內存，間接是指指向該內存的 指針都位于內存泄露處。在上述的例子中，根節點是directly lost，而其他節點是indirectly lost。