如果 _CrtDumpMemoryLeaks() 从未被调用，MFC 项目中的内存泄漏就会消失

Question

我有一个使用 Visual Studio 2017 编译的基于 MFC (C++) 对话框的项目。我添加了以下代码以在构建它时跟踪可能的内存泄漏：

在我的CWinApp 派生类被初始化之前，从ProjectName.cpp 内部开始。

#define _CRTDBG_MAP_ALLOC  
#include <stdlib.h>  
#include <crtdbg.h>
#include <Wtsapi32.h>
#pragma comment(lib, "Wtsapi32.lib")


struct CatchMemLeaks{
    CatchMemLeaks()
    {
        HANDLE ghDebugLogFile = ::CreateFile(L".\\dbg_output.txt", 
            GENERIC_READ | GENERIC_WRITE, 
            FILE_SHARE_READ | FILE_SHARE_WRITE, 
            NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

        //Enable logging into that file
        _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
        _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE | _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE));
        _CrtSetReportFile(_CRT_WARN, ghDebugLogFile);
        _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE | _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE));
        _CrtSetReportFile(_CRT_ERROR, ghDebugLogFile);
        _CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE | _CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE));
        _CrtSetReportFile(_CRT_ASSERT, ghDebugLogFile);


        //Try to break on the error reported
        _CrtSetBreakAlloc(75);
    }

    ~CatchMemLeaks()
    {
        if(_CrtDumpMemoryLeaks())
        {
            DWORD dwRespMsgBx;
            ::WTSSendMessage(NULL, ::WTSGetActiveConsoleSessionId(),
                L"MemLeak", lstrlen(L"MemLeak") * sizeof(WCHAR), 
                L"MemLeak", lstrlen(L"MemLeak") * sizeof(WCHAR),
                MB_OK | MB_ICONERROR | MB_SYSTEMMODAL,
                0, &dwRespMsgBx, TRUE);
        }
    }
};

CatchMemLeaks cml;



//Then the usual MFC CWinApp-app derived class stuff:
// CProjectNameApp

BEGIN_MESSAGE_MAP(CProjectNameApp, CWinApp)
    ON_COMMAND(ID_HELP, &CWinApp::OnHelp)
END_MESSAGE_MAP()


// CProjectNameApp construction

CProjectNameApp::CProjectNameApp()
{
    // support Restart Manager
    m_dwRestartManagerSupportFlags = AFX_RESTART_MANAGER_SUPPORT_RESTART;

    // TODO: add construction code here,
    // Place all significant initialization in InitInstance
}


// The one and only CProjectNameApp object

CProjectNameApp theApp;

//....

然后当项目运行然后退出时，我会触发我的WTSSendMessage：

这给了我以下输出：

Detected memory leaks!
Dumping objects ->
{75} normal block at 0x0000029BA5EA75D0, 16 bytes long.
 Data: <   G            > B0 86 D0 47 F7 7F 00 00 00 00 00 00 00 00 00 00 
{74} normal block at 0x0000029BA5ECE930, 48 bytes long.
 Data: <0       0       > 30 E9 EC A5 9B 02 00 00 30 E9 EC A5 9B 02 00 00 
{73} normal block at 0x0000029BA5EA82F0, 16 bytes long.
 Data: <p  G            > 70 86 D0 47 F7 7F 00 00 00 00 00 00 00 00 00 00 
{72} normal block at 0x0000029BA5ECEA80, 48 bytes long.
 Data: <                > 80 EA EC A5 9B 02 00 00 80 EA EC A5 9B 02 00 00 
{71} normal block at 0x0000029BA5EA8070, 16 bytes long.
 Data: <   G            > 20 86 D0 47 F7 7F 00 00 00 00 00 00 00 00 00 00 
{70} normal block at 0x0000029BA5E98BA0, 120 bytes long.
 Data: <                > A0 8B E9 A5 9B 02 00 00 A0 8B E9 A5 9B 02 00 00 
Object dump complete.

但是在下一次调试运行时，当我添加上面代码中显示的_CrtSetBreakAlloc(75); 行时，错误75 上的断点永远不会触发，尽管输出仍然保持不变。

另一个有趣的发现是，如果我从 ~CatchMemLeaks 析构函数中删除 _CrtDumpMemoryLeaks() 函数，那些内存泄漏就会消失。

PS。我知道这是这个特定项目的特殊之处，因为如果我使用基于 MFC 对话框的股票应用程序尝试它，我不会得到相同的行为。

知道如何跟踪这些泄漏的来源吗？

Answer 1

哎呀，我明白了。 （感谢 cmets 中的@RbMm！）关键是让这个泄漏检测代码在所有其他 CRT 和 MFC 构造函数和其他东西之前初始化（并在之后取消初始化）。诀窍是使用#pragma init_seg(compiler) 指令。我最初的错误是在定义了CWinApp 派生类的.cpp 文件中使用它。这会在应用退出时导致崩溃，因为 #pragma 指令适用于整个 .cpp 文件。

所以解决方案是为我的CatchMemLeaks 类创建一个单独的.h 和.cpp 文件，并在那里设置#pragma 指令，如下所示：

CatchMemLeaks.h文件：

#pragma once

//Only debugger builds
#ifdef _DEBUG

#define _CRTDBG_MAP_ALLOC  
#include <stdlib.h>  
#include <crtdbg.h>  

#include <Strsafe.h>
#include <Wtsapi32.h>
#pragma comment(lib, "Wtsapi32.lib")


struct CatchMemLeaks{
CatchMemLeaks(int nMemLeakCodeToCatch);
~CatchMemLeaks();
};

#endif

和CatchMemLeaks.cpp 文件：

#include "StdAfx.h"
#include "CatchMemLeaks.h"

//Only debugger builds
#ifdef _DEBUG

#pragma warning( push )
#pragma warning( disable : 4074)
#pragma init_seg(compiler)      //Make this code execute before any other code in this project (including other static constructors).
                                //This will also make its destructors run last.
                                //WARNING: Because of this do not call any CRT functions from this .cpp file!
#pragma warning( pop )

CatchMemLeaks cml(0);       //Set to (0) to monitor memory leaks, or to any other value to break on a specific leak number




CatchMemLeaks::CatchMemLeaks(int nMemLeakNumberToBreakOn)
{
    HANDLE ghDebugLogFile = ::CreateFile(.\\dbg_output.txt, 
        GENERIC_READ | GENERIC_WRITE, 
        FILE_SHARE_READ | FILE_SHARE_WRITE, 
        NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

    //Enable logging into that file
    _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE | _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE));
    _CrtSetReportFile(_CRT_WARN, ghDebugLogFile);
    _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE | _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE));
    _CrtSetReportFile(_CRT_ERROR, ghDebugLogFile);
    _CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE | _CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE));
    _CrtSetReportFile(_CRT_ASSERT, ghDebugLogFile);

    if(nMemLeakNumberToBreakOn)
    {
        _CrtSetBreakAlloc(nMemLeakNumberToBreakOn);
    }
}

CatchMemLeaks::~CatchMemLeaks()
{
    //Dump memory leaks, if any
    if(_CrtDumpMemoryLeaks())
    {
            DWORD dwRespMsgBx;
            ::WTSSendMessage(NULL, ::WTSGetActiveConsoleSessionId(),
                L"MemLeak", lstrlen(L"MemLeak") * sizeof(WCHAR), 
                L"MemLeak", lstrlen(L"MemLeak") * sizeof(WCHAR),
                MB_OK | MB_ICONERROR | MB_SYSTEMMODAL,
                0, &dwRespMsgBx, TRUE);
    }
}

#endif

然后最后将其包含在stdafx.h 文件中：

#include "CatchMemLeaks.h"  

Answer 2

您的CatchMemLeaks 类很可能在您程序中的所有其他对象被清理之前被创建然后销毁，因此实际上您报告的是误报（其他对象将在之后被清理）

但如果没有完全运行的程序，就很难判断。