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I frequently change between debug and release build of a large-ish library. Whenever I issue a 

cmake . -DCMAKE_BUILD_TYPE=DEBUG

or the same with RELEASE and do a make, everything is recompiling. I'd like cmake to recompile only the files changed since I built last time with the given mode. Can I do that, and if so, how?

I am using OSX and clang.

Zsolt Szatmari
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1 Answers1

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I believe that the most common solution is have independent build directories for each compile mode (options).

I mean that you need create two directories for this purpose (if your source code stored in ProjectSrc):

ProjectSrc  
└── CMakeList.txt  
ProjectBuild_Debug  
ProjectBuild_Release

Inside ProjectBuild_Debug you need call:

cmake -DCMAKE_BUILD_TYPE=Debug ../ProjectSrc

And Inside ProjectBuild_Release you need call:

cmake -DCMAKE_BUILD_TYPE=Release ../ProjectSrc

Now you can rebuild any type of your program and only files which was changed will be recompiled.

everything is recompiling - everything is recompiling because each file must be compiled with specified compiler options and it's necessary.

Let's look together. For example our project, which build executable file program.exe consist from two source files: one.cpp and two.cpp, both of them have debug output.

  1. You build with release options: one.o and two.o.
  2. You change file one.cpp and rebuild with debug . Now if CMake rebuild only changed files you will get situation when you expect debug version of your program.exe with correct debug output, but it is not, because debug output in file two.o was disabled according last time compilation options.
Gluttton
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  • I don't really want to change build directory if I don't have to, but changing the object file's directory would suffice, I think. Which option does that? – Zsolt Szatmari Jun 19 '14 at 15:36
  • I'm sorry my English is horrendous. I don't clearly understand you question. Do you want store object files in different directories but build executable in the same place? – Gluttton Jun 19 '14 at 15:56
  • Yes. Executable file is expected to be in it's former place (it is a library which is copied elsewhere by a script after build). – Zsolt Szatmari Jun 19 '14 at 16:03
  • Unfortunately I don't know how to achieve this goal. It seams to me that you need declare custom `CMake` directive `add_custom_command`. [This question looks like related](http://stackoverflow.com/questions/9994045/copy-target-file-to-another-location-in-a-post-build-step-in-cmake). – Gluttton Jun 19 '14 at 16:15