What is the proper way to handle `CMAKE_INSTALL_PREFIX` when using the Ninja Multi-Config cmake generator? - cmake

Question

With the cmake generator "Ninja Multi-Config" what is the proper way to handle CMAKE_INSTALL_PREFIX. For instance, if you do:
$ cmake -DCMAKE_INSTALL_PREFIX=../install -G "Ninja Multi-Config" ..
$ cmake --build . --config Release --target install
And then afterwards do
$ cmake --build . --config Debug --target install
will the files in ../install be overwritten by the Debug install? What is the normal way to handle the install location in such cases?

Answer 1

By default they will be overwritten- Ie. with multi-config, the configurations' files install to the same locations.
Command-line "manual" approach
If you don't mind having to do this kind of thing manually on the command-line each time you install, you can just use the --prefix parameter for cmake --install <...>.
From the docs for CMAKE_INSTALL_PREFIX:
The CMAKE_INSTALL_PREFIX may be defined when configuring a build tree to set its installation prefix. Or, when using the cmake(1) command-line tool's --install mode, one may specify a different prefix using the --prefix option.
In that sense, CMAKE_INSTALL_PREFIX can be seen as a default value set per-generated buildsystem that can be overridden on the commandline.
So you can do something like cmake --install <build_dir> --config <config> --prefix <install_dir_unique_to_config>.
defaults in CMakeLists.txt approach
See this CMake mailing thread for various workarounds. Summarized here:
You can (with some exceptions- see the docs) use the <CONFIG>_POSTFIX target property to append a postfix to an output name of a target.
set_target_properties(my_target <more targets can be listed here> PROPERTIES
DEBUG_POSTFIX "-debug"
RELEASE_POSTFIX "-release"
# etc.
)
Workaround using install(DESTINATION) parameters:
install(TARGETS ${LIB_NAME}
CONFIGURATIONS DEBUG
EXPORT ${LIB_NAME}Config-d
PUBLIC_HEADER DESTINATION "include/${LIB_NAME}"
LIBRARY DESTINATION "bin/${LIB_NAME}/debug/"
ARCHIVE DESTINATION "lib/${LIB_NAME}/debug"
)
install(TARGETS ${LIB_NAME}
CONFIGURATIONS RELEASE
EXPORT ${LIB_NAME}Config
PUBLIC_HEADER DESTINATION "include/${LIB_NAME}"
LIBRARY DESTINATION "bin/${LIB_NAME}/release/"
ARCHIVE DESTINATION "lib/${LIB_NAME}/release/"
)