What are the implications of using /Zi vs /Z7 for Visual Studio C++ projects?

Question

Background

There are several different debug flags you can use with the Visual Studio C++ compiler. They are:

• (none)
  • Create no debugging information
  • Faster compilation times
• /Z7
  • Produce full-symbolic debugging information in the .obj files using CodeView format
• /Zi
  
  • Produce full-symbolic debugging information in a .pdb file for the target using Program Database format.
  • Enables support for minimal rebuilds (/Gm) which can reduce the time needed for recompilation.
• /ZI
  
  • Produce debugging information like /Zi except with support for Edit-and-Continue

Issues

• The /Gm flag is incompatible with the /MP flag for Multiple Process builds (Visual Studio 2005/2008)

• If you want to enable minimal rebuilds, then the /Zi flag is necessary over the /Z7 flag.

• If you are going to use the /MP flag, there is seemingly no difference between /Z7 and /Zi looking at MSDN. However, the SCons documentation states that you must use /Z7 to support parallel builds.

Questions

• What are the implications of using /Zi vs /Z7 in a Visual Studio C++ project?

• Are there other pros or cons for either of these options that I have missed?

• Specifically, what is the benefit of a single Program Database format (PDB) file for the target vs multiple CodeView format (.obj) files for each source?

References

MDSN /Z7, /Zi, /ZI (Debug Information Format)

MSDN /MP (Build with Multiple Processes)

SCons Construction Variables CCPDBFLAG

http://www.debuginfo.com/articles/gendebuginfo.html

Answer 1

Codeview is a much older debugging format that was introduced with Microsoft's old standalone debugger back in the "Microsoft C Compiler" days of the mid-1980s. It takes up more space on disk and it takes longer for the debugger to parse, and it's a major pain to process during linking. We generated it from our compiler back when I was working on the CodeWarrior for Windows in 1998-2000.

The one advantage is that Codeview is a documented format, and other tools can often process it when they couldn't deal with PDB-format debug databases. Also, if you're building multiple files at a time, there's no contention to write into the debug database for the project. However, for most uses these days, using the PDB format is a big win, both in build time and especially in debugger startup time.

Answer 2

One advantage of the old C7 format is that it's all-in-one, stored in the EXE, instead of a separate PDB and EXE. This means you can never have a mismatch. The VS dev tools will make sure that a PDB matches its EXE before it will use it, but it's definitely simpler to have a single EXE with everything you need.

This adds new problems of needing to be able to strip debug info when you release, and the giant EXE file, not to mention the ancient format and lack of support for other modern features like minrebuild, but it can still be helpful when you're trying to keep things as simple as possible. One file is easier than two.

Not that I ever use C7 format, I'm just putting this out there as a possible advantage, since you're asking.

Incidentally, this is how GCC does things on a couple platforms I'm using. DWARF2 format buried in the output ELF's. Unix people think they're so hilarious. :)

BTW the PDB format can be parsed using the DIA SDK.