[cmake] Copy file from source directory to binary directory using CMake

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?

I would suggest TARGET_FILE_DIR if you want the file to be copied to the same folder as your .exe file.

$ Directory of main file (.exe, .so.1.2, .a).

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

In VS, this cmake script will copy input.txt to the same file as your final exe, no matter it's debug or release.

if you want to copy folder from currant directory to binary (build folder) folder

file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/yourFolder/ DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/yourFolder/)

then the syntexe is :

file(COPY pathSource DESTINATION pathDistination)

If you want to put the content of example into install folder after build:

code/
  src/
  example/
  CMakeLists.txt

try add the following to your CMakeLists.txt:

install(DIRECTORY example/ DESTINATION example)

The first of option you tried doesn't work for two reasons.

First, you forgot to close the parenthesis.

Second, the DESTINATION should be a directory, not a file name. Assuming that you closed the parenthesis, the file would end up in a folder called input.txt.

To make it work, just change it to

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

The suggested configure_file is probably the easiest solution. However, it will not rerun the copy command to if you manually deleted the file from the build directory. To also handle this case, the following works for me:

add_custom_target(copy-test-makefile ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/input.txt)
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
                   DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/input.txt)

This is what I used to copy some resource files: the copy-files is an empty target to ignore errors

 add_custom_target(copy-files ALL
    COMMAND ${CMAKE_COMMAND} -E copy_directory
    ${CMAKE_BINARY_DIR}/SOURCEDIRECTORY
    ${CMAKE_BINARY_DIR}/DESTINATIONDIRECTORY
    )

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

1. file(COPY ... copies the file in 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