CPack与install(CODE)场景下，是否存在统一指向当前安装目录的CMake变量？

Great question! This is a super common gotcha when mixing CMake's install() hooks with CPack—let me break down what's happening and how to fix it.

Why the Path Breaks with CPack #

When you run the regular install target, ${CMAKE_INSTALL_PREFIX} points directly to where files are being installed. But CPack works differently: it first installs your project into a temporary staging directory (using the DESTDIR environment variable under the hood) before packaging it up. Your original install(CODE) command is looking for files in the final install path, not the temporary staging directory where CPack actually puts them.

The Standard Fix: Combine DESTDIR and CMAKE_INSTALL_PREFIX #

There isn't a built-in ${CMAKE_CURRENT_INSTALL_PREFIX} variable that does exactly what you're asking, but you can use the combination of $ENV{DESTDIR} and ${CMAKE_INSTALL_PREFIX} to get the correct install directory in both scenarios. Here's how to adjust your command:

install(CODE "execute_process(COMMAND some_command \"$ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/some_folder\")")

This works because:

• When running a regular install (e.g., make install without extra flags), $ENV{DESTDIR} is empty, so the path resolves to ${CMAKE_INSTALL_PREFIX}/some_folder—just like your original command.
• When CPack runs, it sets DESTDIR to its temporary staging directory, so the path becomes the exact location where your installed files live during packaging.

For Complex Logic: Use a Separate Script #

If your post-install step is more involved (like adding error checking), move the logic into a dedicated CMake script file instead of embedding it directly in install(CODE):

1. Create a GenerateCache.cmake file with your logic:

execute_process(
    COMMAND some_command "${DESTDIR}${CMAKE_INSTALL_PREFIX}/some_folder"
    RESULT_VARIABLE CACHE_GENERATION_RESULT
)
if(NOT CACHE_GENERATION_RESULT EQUAL 0)
    message(FATAL_ERROR "Failed to generate cache file for some_folder!")
endif()

2. Reference the script in your CMakeLists.txt:

install(SCRIPT ${CMAKE_CURRENT_SOURCE_DIR}/GenerateCache.cmake)

This keeps your main build config cleaner and makes debugging easier.

内容的提问来源于stack exchange，提问作者Patrick Storz