cmake: regenerate file with each build

Question

generated.h is created by a script replaced with touch for now. How can I achieve that this file is regenrated each time I run make ? Calling rm like in the below example produces error.

cmake_minimum_required(VERSION 3.5.1)
project(MyProject)

set_source_files_properties(generated.h PROPERTIES GENERATED TRUE)

add_executable(jr
    jr.cpp
    generated.h
    )

add_custom_command(
        OUTPUT generated.h
        COMMAND rm generated.h
        COMMAND touch generated.h
        )

Answer 1

Instead of add_custom_command use add_custom_target : it will be executed every time build is run:

add_custom_target(regenerate
    COMMAND rm -f generated.h # Remove file if it exists.
    COMMAND touch generated.h
)

# Force executable to be compiled after regeneration takes a place
add_dependencies(jr regenerate)

# You need to hint compiler about location of the header file generated.
include_directories(${CMAKE_CURRENT_BINARY_DIR})