How to debug in release mode?

Question

I have to debug a c++ project, but as one dependency doesn't compile in debug mode and I haven't been able to fix that issue so far, I'd like to try to debug the project in release mode.

Currently the application crashes due to a null pointer, but I haven't the code that's causing the error. As break points apparently are ignored in release-mode, I'd like to know what's the best way find the error.

Answer 1

In VS, right click your project, chose "Properties".

1. Click the C/C++ node. Set Debug Information Format to C7 compatible (/Z7) or Program Database (/Zi).

2. Expand Linker and click the General node. Set Enable Incremental Linking to No (/INCREMENTAL:NO).

3. Select the Debugging node. Set Generate Debug Info to Yes (/DEBUG).

4. Select the Optimization node. Set References to Yes (/OPT:REF).

   if /OPT:REF is specified, /OPT:ICF is on by default.

That's ripped directly from Microsoft's documentation:

• How to: Debug a Release Build
• OPT Optimizations

I do this all of the time and pretty much never debug in debug mode anymore. As you know, many errors that occur in a release build may not occur in a debug build (almost certainly the errors that arise from invoking UB).

Also, I work on a project which uses a ton of image processing and performs a lot of compression/decompression of large images. Using a slow debug build is simply impractical.

Answer 2

You can't always just change the project settings and recompile.
Sometimes you have a released version which you would like to debug, or a dump file sent by a client.

When compiling a C++ project in release with optimizations, the debugger sometimes doesn't show the right object information.

The local variables are usually the first to go, and many times, the this object's information is lost to the debugger.

The reason is that the compiler uses the available hardware registers to hold the information, and uses optimizations to avoid allocation of local variables.

I've suggested a way to find the missing information here:

Debugging Release Projects in C++ - Finding the Lost Object Information