What is usage of this macro DEBUG_NEW in visual C++/MFC?

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I am working on a legacy C++ project and saw these statement on top of a header file:

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

I know it is related with debugging memory leaks stuff, but not sure how it works, or potentially it can be used for other purpose too.

Post here to ask C++ gurus to get more insights.

thanks a million!

What I have tried:

play around with this code snippet and did not find much details on how it is used in this project.

Posted 17-Dec-20 6:10am

Southmountain

Updated 8-Mar-22 23:58pm

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5 solutions

Solution 1

If you right click on it in Visual Studio you can go to the definition. It is a wrapper for the new operator, and captures some extra debug information every time new is called in the application.

Posted 17-Dec-20 6:17am

Richard MacCutchan

Comments

Southmountain 17-Dec-20 12:48pm

if I put cursor on DEBUG_NEW, a tooltip prompts: #define DEBUG_NEW new(this_file, _LINE_),
so all keyword new will be replaced by new(this_file, _LINE_)?

Richard MacCutchan 17-Dec-20 13:46pm

Yes. It captures extra information to help debug problems with memory allocations.

Solution 3

For a little bit more info check this out : Memory Allocation Tracking for C++ Code[^] (Shameless plug).

The macros shown there are slightly revised from the default implementation of the DEBUG_NEW macro. The THIS_FILE declarations are no longer used by MFC, AFAIK.

Posted 17-Dec-20 6:51am

Rick York

Comments

Southmountain 17-Dec-20 12:55pm

thank you for this post! my 5!

Solution 4

To make a long story short, when your output window prints: Detected memory leaks, double clicking that error will take you to the line where you used the "new" operator in your source code. Hence all that __FILE__ and __LINE__ business

Posted 17-Dec-20 16:42pm

steveb

Comments

Southmountain 18-Dec-20 11:44am

this is the trick that I will master. thank you very much!

Solution 5

NOTE: As of C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\atlmfc\include

"THIS_FILE" is still used by MFC...

Posted 8-Mar-22 23:58pm

TheCPUWizard

Comments

CHill60 9-Mar-22 6:27am

This should have been posted as a comment to Solution 3. It is not, in itself, a solution to the question posed

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CPallini · Accepted Answer · 2020-12-17T06:19:00

Solution 2

As external link to the very macro Wikipedia page[^] you may find A Cross-Platform Memory Leak Detector[^] that may give you some insight.

Posted 17-Dec-20 6:19am

CPallini

v2

Comments

Southmountain 17-Dec-20 12:29pm

thanks for these good links!

CPallini 17-Dec-20 13:31pm

You are welcome.