Editing versus deleting CMakeCache.txt after moving directory

Question

If CMake is re-executed after the source directory is moved, an error like this is given:

CMake Error: The current CMakeCache.txt directory /new-path/CMakeCache.txt is different than the directory /old-path where CMakeCache.txt was created. This may result in binaries being created in the wrong place. If you are not sure, reedit the CMakeCache.txt

What is the best approach to deal with this? It seems that deleting the cache works. Why might I want to edit CMakeCache.txt, rather than just delete it?

Answer 1

I think your best bet is indeed to delete the cache and re-create it. In fact, I tend to go further and remove the entire build tree if I need to move the source, but this is probably overkill.

The CMakeCache.txt file can be edited via the CMake GUI or by hand if you're sure what you're doing, but I find it's not usually worth the effort compared to re-running cmake from scratch. I guess if running CMake takes a significant amount of time (e.g. if you use ExternalProject_Add which could involve downloading and building a third-party resource), it may be preferable to modify the CMakeCache.txt.

This article provides a bit more detail about the CMakeCache.txt file and editing it. In particular it says:

The main reason for editing the cache would be to give CMake the location of a native library such as JPEG, or to stop it from using a native library and use a version of the library in your source tree.

CMake will not alter an existing entry in the cache file itself. If your CMakeLists.txt files change significantly, you will need to remove the relevant entries from the cache file. If you have not already hand-edited the cache file, you could just delete it before re-running CMake.