Cmake Generator Expressions

Question

I have been trying for a long time to understand the benefits of generator expressions , such as $<xxx:yy> in CMake, when and how to use them. Can someone explain this with some examples. Many are grateful in advance

Answer 1

CMake first parses the CMakeLists.txt files in your project called “Configuration Phase,” and then generates your build environment called “Generation Phase.”

So basically the generator expressions are for everything the generator could know:

• The name and path of the target outputs (mainly in cross-compilation and in multi-configuration environments)
• Or, as a rule, any target property that the generator evaluates to mix the compiler / linker calls

Here are examples of using generator expressions in my project:

• Copying files next to an executable file (in environments with multiple configurations, you cannot just use variables like CMAKE_CURRENT_BINARY_DIR )

   add_custom_command( TARGET library1 POST_BUILD COMMAND ${CMAKE_COMMAND} -E copy "$<TARGET_FILE:library1>" "$<TARGET_FILE_DIR:mainProject>/$<TARGET_FILE_NAME:library1>" ) 

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   add_custom_command( TARGET myBinary POST_BUILD COMMAND ${CMAKE_COMMAND} -E copy "${CMAKE_CURRENT_SOURCE_DIR}/myTest.txt" "$<TARGET_FILE_DIR:myBinary>/myTest.txt" ) 

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• Distinguish, for example. DEBUG or RELEASE configuration

   add_compile_options("$<$<CONFIG:DEBUG>:/MDd>") 

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• With the TARGET_PROPERTY generator TARGET_PROPERTY you can do many things, for example.

   file(GENERATE OUTPUT "includes.txt" CONTENT "$<TARGET_PROPERTY:motor,INCLUDE_DIRECTORIES>\n" ) 

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