How do I debug an MFC extension DLL?

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Hi,

I'm creating an application using C++ and MFC. My app loads several MFC extension DLL from its "Plugins" folder during execution, and the user can choose which one he wants to launch in a list.
However, if someone wants to make a MFC extension DLL for my app, and only have the executable (not the source code), how can this person debug its MFC extension DLL?

What I have tried:

I tried to follow this procedure:

In Solution Explorer, select the DLL project.
From the View menu, choose Property Pages.
In the <Project> Property Pages dialog box, in the Configuration drop-down list box, choose Debug.
Open the Configuration Properties folder and select the Debugging category.
In the Command box, click the drop down arrow and choose Browse from the list to browse for the application.
Enter any necessary program arguments in the Command Arguments box.

from microsoft website. I also added my .dll in the "Plugins" folder of my app.
But it didn't work, and my app couldn't load any plugin from its folder.

Posted 28-Sep-17 3:25am

SheepSpeech

Updated 28-Sep-17 5:11am

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Rick York · Answer 1 · 2017-09-28T05:11:00

Solution 1

You have to supply them a debug version of your executable because MFC can't mix debug and release mode modules. You don't have to supply them your source code though and I am not sure whether you have to supply them a symbol file, the .pdb. They have to make a debug build and specify command, arguments, and working directory in the debugging section of the configuration properties then they can set breakpoints in the interface methods and debug their library.

You can test this yourself by making a little skeleton library with all of the required interface methods and see if it works. It should be fairly simple. You will have to experiment to see what the extension library needs from your app in terms of .pdb files and such.

Posted 28-Sep-17 5:11am

Rick York

Comments

SheepSpeech 29-Sep-17 4:05am

Hi,

I think it is what I've done (did I forget something? May be the .pdb files but I wasn't explicitly blocked without it).
The problem is more into this: my app loads plugins from its "Plugins" directory and then the user can choose one of them and launch it. So only attaching my extension to the app do not allow me to see the plugin in my app. Moreover, doing this way, my app doesn't load any plugin (usually, it loads all the plugins available in its "Plugins" directory).

Rick York 29-Sep-17 10:29am

I will admit that it can get tricky but I have done exactly this myself in the past so I know it's possible. You can debug the DLLs in two ways. One is set a breakpoint in your code where you invoke functions from the DLL and then step into the code that it calls. The second is to set a breakpoint inside the functions of the DLL and then run the program until one of those breakpoints is hit. Either way is fairly simple. Give one or both a try and see what happens.

SheepSpeech 29-Sep-17 10:36am

Did you try this without the main app's source code? Thanks.

Rick York 29-Sep-17 16:07pm

Not that I recall. Have you? It's a quick and easy thing to do. I described how earlier.

SheepSpeech 2-Oct-17 4:49am

This is what I understand:

"One is set a breakpoint in your code where you invoke functions from the DLL and then step into the code that it calls." You need to have the main app's source code for this.

"The second is to set a breakpoint inside the functions of the DLL and then run the program until one of those breakpoints is hit." You need to be able to run the debugguer from the DLL, to do this you have to attach the DLL to the app, but as I explained the app doesn't launch it in this case because it's not in its Plugins directory. If you also put the .dll in its Plugins directory and choose to launch it from the app, breakpoints are ignored.

Rick York 2-Oct-17 13:15pm

Unfortunately, I am not in a good position to write a program to test this. However, I did a little searching and found a number of articles on this topic. I searched here for the words "plug-in framework" and found quite a few articles. I recommend getting one of them and test out what you are trying to do and see what happens. I often find that testing in the smallest possible environment can be very beneficial as it tends to minimize side effects.