memcheck工具的使用方式如下:
valgrind --tool=memcheck ./a.out
从上面的命令可以清楚的看到, 主要的命令是valgrind,而我们想使用的工具是通过'-tool'选项来指定的. 上面的‘a.out’指的是我们想使用memcheck运行的可执行文件.
该工具可以检做腔肆测下列与内存相关的问题 :
未释放内存的使用
对释放后内存的读/写
对已分配内存块尾部的读/写
内存泄露
不匹配的使用malloc/new/new[] 和 free/delete/delete[]
重复释放内存
注意: 上面列出的并不很全面,但却包含了能被该工具检测到的很多普遍的问题.
让我们一个一个地对上面的场景进行讨论:
注意: 下面讨论的所有测试代码都应该使用gcc并且加上-g选圆租项(用来在memcheck的输出中生成行号)进行编译. 就想我们之前讨论过的 C程序被编译成可执行文件, 它需要经历四个不同的阶段.
ToB蓝波湾
翻译于 1 年 前
0人顶
顶 翻译的不错哦!
1. 使用未初始化的内存
Code :
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char *p
char c = *p
printf("\n [%c]\n",c)
return 0
}
在上面的代码中,我们尝试使用未初始化的指针 ‘p’.
让我们运行Memcheck来看下结果.
$ valgrind --tool=memcheck ./val
==2862== Memcheck, a memory error detector
==2862== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==2862== Using Valgrind-3.6.0.SVN-Debian and LibVEXrerun with -h for copyright info
==2862== Command: ./val
==2862==
==2862== Use of uninitialised value of size 8
==2862==at 0x400530: main (valgrind.c:8)
==2862==
[#]
==2862==
==2862== HEAP SUMMARY:
==2862== in use at exit: 0 bytes in 0 blocks
==2862== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==2862==
==2862== All heap blocks were freed -- no leaks are possible
==2862==
==2862== For counts of detected and suppressed errors, rerun with: -v
==2862== Use --track-origins=yes to see where uninitialized values come from
==2862== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)
从上面的输出可以看到,Valgrind检测到了未初始化的变量,然后给出了警告(上面加粗的几行(译者注:貌似上面没有加粗的)).
2. 在内存被释放后进行读/写
Code :
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char *p = malloc(1)
*p = 'a'
char c = *p
printf("\n [%c]\n",c)
free(p)
c = *p
return 0
}
上面的代码中,我们纯轿有一个释放了内存的指针 ‘p’ 然后我们又尝试利用指针获取值.
让我们运行memcheck来看一下Valgrind对这种情况是如何反应的.
$ valgrind --tool=memcheck ./val
==2849== Memcheck, a memory error detector
==2849== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==2849== Using Valgrind-3.6.0.SVN-Debian and LibVEXrerun with -h for copyright info
==2849== Command: ./val
==2849==
[a]
==2849== Invalid read of size 1
==2849==at 0x400603: main (valgrind.c:30)
==2849== Address 0x51b0040 is 0 bytes inside a block of size 1 free'd
==2849==at 0x4C270BD: free (vg_replace_malloc.c:366)
==2849==by 0x4005FE: main (valgrind.c:29)
==2849==
==2849==
==2849== HEAP SUMMARY:
==2849== in use at exit: 0 bytes in 0 blocks
==2849== total heap usage: 1 allocs, 1 frees, 1 bytes allocated
==2849==
==2849== All heap blocks were freed -- no leaks are possible
==2849==
==2849== For counts of detected and suppressed errors, rerun with: -v
==2849== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)
从上面的输出内容可以看到,Valgrind检测到了无效的读取 *** 作然后输出了警告 ‘Invalid read of size 1′.
另注,使用gdb来调试c程序.
3. 从已分配内存块的尾部进行读/写
Code :
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char *p = malloc(1)
*p = 'a'
char c = *(p+1)
printf("\n [%c]\n",c)
free(p)
return 0
}
在上面的代码中,我们已经为‘p’分配了一个字节的内存,但我们在将值读取到 ‘c’中的时候使用的是地址p+1.
现在我们使用Valgrind运行上面的代码 :
$ valgrind --tool=memcheck ./val
==2835== Memcheck, a memory error detector
==2835== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==2835== Using Valgrind-3.6.0.SVN-Debian and LibVEXrerun with -h for copyright info
==2835== Command: ./val
==2835==
==2835== Invalid read of size 1
==2835==at 0x4005D9: main (valgrind.c:25)
==2835== Address 0x51b0041 is 0 bytes after a block of size 1 alloc'd
==2835==at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==2835==by 0x4005C5: main (valgrind.c:22)
==2835==
[]
==2835==
==2835== HEAP SUMMARY:
==2835== in use at exit: 0 bytes in 0 blocks
==2835== total heap usage: 1 allocs, 1 frees, 1 bytes allocated
==2835==
==2835== All heap blocks were freed -- no leaks are possible
==2835==
==2835== For counts of detected and suppressed errors, rerun with: -v
==2835== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)
同样,该工具在这种情况下也检测到了无效的读取 *** 作.
4. 内存泄露
Code:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char *p = malloc(1)
*p = 'a'
char c = *p
printf("\n [%c]\n",c)
return 0
}
在这次的代码中, 我们申请了一个字节但是没有将它释放.现在让我们运行Valgrind看看会发生什么:
$ valgrind --tool=memcheck --leak-check=full ./val
==2888== Memcheck, a memory error detector
==2888== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==2888== Using Valgrind-3.6.0.SVN-Debian and LibVEXrerun with -h for copyright info
==2888== Command: ./val
==2888==
[a]
==2888==
==2888== HEAP SUMMARY:
==2888== in use at exit: 1 bytes in 1 blocks
==2888== total heap usage: 1 allocs, 0 frees, 1 bytes allocated
==2888==
==2888== 1 bytes in 1 blocks are definitely lost in loss record 1 of 1
==2888==at 0x4C274A8: malloc (vg_replace_malloc.c:236)
==2888==by 0x400575: main (valgrind.c:6)
==2888==
==2888== LEAK SUMMARY:
==2888==definitely lost: 1 bytes in 1 blocks
==2888==indirectly lost: 0 bytes in 0 blocks
==2888== possibly lost: 0 bytes in 0 blocks
==2888==still reachable: 0 bytes in 0 blocks
==2888== suppressed: 0 bytes in 0 blocks
==2888==
==2888== For counts of detected and suppressed errors, rerun with: -v
==2888== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)
输出行(上面加粗的部分)显示,该工具能够检测到内存的泄露.
本文浅谈一下C 内存泄漏的检测,首先我们需要知道程序有没有内存泄露,然后定位到底是哪行代码出现内存泄露了,这样才能将其修复。最简单的方法当然是借助于专业的检测工具,比较有名如BoundsCheck工具,功能非常强大,相信做C 开发的人都离不开它。此外就是不使用任何工具,而是自己来实现对内存泄露的监控,分如下两种情况:一. 在 MFC 中检测内存泄漏假如是用MFC的程序的话,很简单。默认的就有内存泄露检测的功能。我们用VS2005生成了一个MFC的对话框的程序,发现他可以自动的检测内存泄露.不用我们做任何特殊的 *** 作桥汪. 仔细观察,发现在每个CPP文件中,都有下面的代码:#ifdef _DEBUG #define new DEBUG_NEW #endifDEBUG_NEW 这个宏定义在afx.h文件中,就是它帮助我们定位内存泄漏。 在含有以上代码的cpp文件中分配行消歼内存后假如没有删除,那么停止程序的时候,VisualStudio的Output窗口就会显示如下的信息了:Detected memory leaks! Dumping objects ->d:\code\mfctest\mfctest.cpp(80) : {157} normal block at 0x003AF170, 4 bytes long. Data: <>00 00 00 00 Object dump complete.在Output窗口双击粗体字那一行,那么IDE就会打开该文件,定位到该行,很容易看出是哪出现了内存泄露。二.检测纯C 的程序内存泄露我试了下用VisualStudio建立的Win32 Console Application和Win32 Project项目,结果都不能检测出内存档冲泄露。下面一步一步来把程序的内存泄露检测的机制建立起来。首先,我们需要知道C运行库的Debug版本提供了许多检测功能,使得我们更容易的Debug程序。在MSDN中有专门的章节讲这个,叫做Debug Routines,建议大家先看看里面的内容吧。我们会用到里面很重要的几个函数。欢迎分享,转载请注明来源:内存溢出
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