Copy file from source directory to binary directory using CMake

Question

I'm trying to create a simple project on CLion. It uses CMake (I'm new here) to generate Makefiles to build project (or some sort of it)

All I need to is transfer some non-project file (some sort of resource file) to binary directory each time when I run the my code.

That file contains test data and application open it to read them. I tried several ways to do so:

• Via file(COPY ...

  file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/input.txt
          DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/input.txt
  

  Looking good but it work just once and not recopy file after next run.

• Via add_custom_command

  • OUTPUT version

    add_custom_command(
            OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/input.txt
            COMMAND ${CMAKE_COMMAND} -E copy
                    ${CMAKE_CURRENT_SOURCE_DIR}/input.txt
                    ${CMAKE_CURRENT_BINARY_DIR}/input.txt)
    

  • TARGET version

    add_custom_target(foo)
    add_custom_command(
            TARGET foo
            COMMAND ${CMAKE_COMMAND} copy
                    ${CMAKE_CURRENT_BINARY_DIR}/test/input.txt
                    ${CMAKE_SOURCE_DIR})
    

  But no one of it work.

What am I doing wrong?

Answer 1

You may consider using configure_file with the COPYONLY option:

configure_file(<input> <output> COPYONLY)

Unlike file(COPY ...) it creates a file-level dependency between input and output, that is:

If the input file is modified the build system will re-run CMake to re-configure the file and generate the build system again.

Answer 2

Both option are valid and targeting two different steps of your build:

1. file(COPY ... copies the file during the configuration step and only in this step. When you rebuild your project without having changed your cmake configuration, this command won't be executed.
2. add_custom_command is the preferred choice when you want to copy the file around on each build step.

The right version for your task would be:

add_custom_command(
        TARGET foo POST_BUILD
        COMMAND ${CMAKE_COMMAND} -E copy
                ${CMAKE_SOURCE_DIR}/test/input.txt
                ${CMAKE_CURRENT_BINARY_DIR}/input.txt)

you can choose between PRE_BUILD, PRE_LINK, POST_BUILD best is you read the documentation of add_custom_command

An example on how to use the first version can be found here: Use CMake add_custom_command to generate source for another target