What is the in-place/Out-of-place builds

Question

As in the title the questions is what is the difference between (in-place/Out-of-place builds)?

Answer 1

An in-place build generates the various compiled files (.o/.obj files, executables, &c.) in the same directory as the source tree.

An out-of-place build generates them in some directory that is not the source directory. This means that you can have several out-of-place builds that all point back to the same source tree, which is not possible once you have an in-place build.

See also: The CMake FAQ.