Examples to Try Out
Understand how to apply generator expressions in CMake through practical examples covering build configurations, system-specific compiler flags, interface libraries, and nesting. Learn to debug complex expressions and distinguish between conditional and Boolean evaluations for cleaner, more efficient project builds.
Everything is easier to grasp when there's a good practical example to support the theory. Here are some of the uses for generator expressions:
Build configurations
There may be cases where we'd like to act differently based on what kind of build (Debug, Release, and so on) we're making.
A simple and easy way to do so is by utilizing the $<CONFIG> generator expression:
target_compile_options(tgt $<$<CONFIG:DEBUG>:-ginline-points>)
The preceding example checks whether the config equals DEBUG; if that's the case, the nested expression is evaluated to 1. The outer shorthand if expression then becomes true, and our -ginline-points debug flag gets added to the options.
System-specific one-liners
Generator expressions can also be used to compact verbose if commands into neat one-liners. Let's suppose we have the following code:
if (${CMAKE_SYSTEM_NAME} STREQUAL "Linux")target_compile_definitions(myProject PRIVATE LINUX=1)endif()
It tells the compiler to add -DLINUX=1 to the arguments if this is the target system. While this isn't terribly long, it could be easily replaced with an elegant ...