What is the difference between CMake's -S and -H option?

Question

I searched a long time for a way of changing CMake's build directory without cding into it.

I eventually find the -H option and make my scripts with it. Now I typed in cmake --help and I directly have seen following output:

$ cmake --help
Usage

  cmake [options] <path-to-source>
  cmake [options] <path-to-existing-build>
  cmake [options] -S <path-to-source> -B <path-to-build>

I recently use:

$ cmake --version
cmake version 3.14.0

CMake suite maintained and supported by Kitware (kitware.com/cmake).

and I think in older version this was missing.

Nevertheless, I wonder if there is any difference between -H and -S option. Furthermore I wonder if they are safe to use at all. I found this questions in other posts, but it has not been answered (e.g. here: How to tell CMake where to put build files?)

Answer 1

-H option is not documented and exists long before -S option. It was somewhat considered a "trick" before -S option existed. The -H option purpouse was to make developers life easier, but they left it in release builds, so people started using it. Since cmake 3.13 (I think it's Novemeber 2018) the -S option is available, making -H obsolete (or not? I don't know what the intention of cmake developers is).

Seeing cmake sources the -H and -S option act exactly the same.