Introduction

If there are memory leaks again, just link the DLL from the MemoryLeakIndicator to the project (I use the MemoryLeakIndicator only in debug mode).

In the main file include MliForMain.h, in the implementation files where something is instantiated with new, after all other includes only the MilDebugNew.h.

In the respective project the MilNewDelete.cpp must be compiled as well.

The English text was translated with the support of www.DeepL.com.

Motivation

I use with Visual Studio on Windows the crtdbg.h to get memory leaks displayed.

See also: https://github.com/MicrosoftDocs/visualstudio-docs/blob/main/docs/debugger/finding-memory-leaks-using-the-crt-library.md

Unfortunately, the file name and the line number are only displayed in the Visual Studio output-window when using malloc, but not when using new. In the case of memory leaks caused by a new, only the address and the data are displayed. While it is possible to assign the value from the curly brackets to the variable _crtBreakAlloc in the hope that the program stops at the place where the non-deleted object is instantiated. But this is unfortunately not always reliable (e.g. with DLLs), since if necessary always another memory location is taken.

Finding the causing instructions in the source code is sometimes difficult. I would like to have the file name and the line number as a hint.

implementation

If there are memory leaks again, just link the DLL from the MemoryLeakIndicator to the project.

In addition, the source file MilNewDelete.cpp (with the overloaded operators new and delete) must also be compiled in the project.

This also applies to self-created DLLs if memory leaks are to be detected there.

In the main file include MliForMain.h, in the implementation files where something is instantiated with new, after all other includes only the MilDebugNew.h. I enclose this with a preprocessor statement such as:

#if defined _MSC_VER && defined _DEBUG_MEMORY_SPY
  ...
#endif

Note: It is not crowned with success to take over all sources of MemoryLeakIndicator into the own project, thus not to use the DLL.

Example

Here is a small example:

#if defined _MSC_VER && defined _DEBUG
  // detect Memory-Leaks
  #define _CRTDBG_MAP_ALLOC
  #include <crtdbg.h>
#endif

#include <iostream>
#include <string>
#include <conio.h>
#if defined _MSC_VER && defined _DEBUG_MEMORY_SPY
  #include <MliForMain.h>
#endif
//-----------------------------------------------------------------------------
class MyClass
{
  private:
    int * m_piT1;
  public:
    MyClass( int i )
    {
      m_piT1 = new int (i);
    };
    ~MyClass()
    {
      // Oh, m_piT1 forgot to delete
      //delete m_piT1;
    };
};
//-----------------------------------------------------------------------------
int main(int argc, char *argv[])
{
  #if defined _MSC_VER && defined _DEBUG
    // Displays memory leaks when there are any...
    _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF );
    // Comment out next line with number from { } -> e.g..: "{173} normal block at 0x00D01C78, 10 bytes long."
    //_crtBreakAlloc = 172;
    // Is unfortunately not always (e.g. with DLLs) reliably, because if necessary other memory location.
  #endif

  #if defined _MSC_VER && defined _DEBUG_MEMORY_SPY
    MemSpy::activateMemoryMonitoring();
  #endif

  // Examples:
  MyClass * t_pClass = new MyClass( 1 );
  //delete t_pClass;

  int * t_piLeak = new int( 2 );
  //delete t_piLeak;

  char * t_szLeak = new char[100];
  //delete[] t_szLeak;

  #if defined _MSC_VER && defined _DEBUG_MEMORY_SPY
    // Display memory leaks
    MemSpy::finishMemoryMonitoring( MemSpy::OUTPUT_TRACE | MemSpy::OUTPUT_CONSOLE );
  #endif
  std::cout << "press any key . . .";
  _getch();
  return 0;
}
//-----------------------------------------------------------------------------

Since the parameters MemSpy::OUTPUT_TRACE and MemSpy::OUTPUT_CONSOLE were passed to the MemSpy::finishMemoryMonitoring(...) function, at the end of the example program, the memory leaks are displayed in the console and in the VisualStudio output window.

Der Thread 15572 hat mit Code 0 (0x0) geendet.
                                                                     
  Memory leaks detected!                                            *
                                                                     
  Memory leak in 1313691209200, file D:\Projekte\C++\Src\MemoryLeakIndicator\source\main.cpp, line 45
  Memory leak in 1313691165808, file D:\Projekte\C++\Src\MemoryLeakIndicator\source\main.cpp, line 21
  Memory leak in 1313691166000, file D:\Projekte\C++\Src\MemoryLeakIndicator\source\main.cpp, line 48
  Memory leak in 1313691152224, file D:\Projekte\C++\Src\MemoryLeakIndicator\source\main.cpp, line 51
                                                                     
"MemoryLeakIndicatorDllTestd.exe" (Win32): "C:\Windows\System32\kernel.appcore.dll" geladen. 
"MemoryLeakIndicatorDllTestd.exe" (Win32): "C:\Windows\System32\msvcrt.dll" geladen. 
"MemoryLeakIndicatorDllTestd.exe" (Win32): "C:\Windows\System32\rpcrt4.dll" geladen. 
Der Thread 10624 hat mit Code 0 (0x0) geendet.
Der Thread 17076 hat mit Code 0 (0x0) geendet.
Detected memory leaks!
Dumping objects ->
{172} normal block at 0x00000131DE182F60, 100 bytes long.
 Data: <                > CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD 
{171} normal block at 0x00000131DE186530, 4 bytes long.
 Data: <    > 02 00 00 00 
{170} normal block at 0x00000131DE186470, 4 bytes long.
 Data: <    > 01 00 00 00 
{169} normal block at 0x00000131DE190DF0, 8 bytes long.
 Data: <pd  1   > 70 64 18 DE 31 01 00 00 
Object dump complete.
Das Programm "[15928] MemoryLeakIndicatorDllTestd.exe" wurde mit Code 0 (0x0) beendet.

Note: If you create objects in modern C++ projects and pass them on if necessary, you do not use simple pointers if possible, but smart pointers like std::unique_ptr or std::shared_ptr.As a rule, the specifications of RAII should be followed.

See also: https://docs.microsoft.com/en-us/cpp/cpp/object-lifetime-and-resource-management-modern-cpp?view=msvc-170
https://docs.microsoft.com/en-us/cpp/cpp/how-to-create-and-use-shared-ptr-instances?view=msvc-170

Limitations

I failed to overload the new (std::nothrow). When dealing with custom code, this new operator must either be modified for this purpose (without std::nothrow), or MilDebugNew.h is not included.
Every now and then, especially in multi-threaded applications, the MemoryLeakIndicator shows fake memory leaks. These are recognizable if you run the application in debug mode using crtdbg.h and there is no additional output in the output in the VisualStudio output window such as:

…
Detected memory leaks!
Dumping objects →
{172} normal block at 0x00000131DE182F60, 100 bytes long.
  Data: < > CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD
...

Trials with MinGW and GCC have also failed for me; only works with VisualStudio C++. If anyone is willing to adapt MemoryLeakIndicator to other compilers, I'd appreciate it.