Hi,

It appears you can use CMake to quickly generate preprocessed source of your chosen .cpp file without modifying the CMakeLists.txt project file. This trick works only when your generator is make -- meaning, it won't work with the ninja builder.

But still, if you're using make as your generator, try the following.

First, create a sample source code (~/dev/project/test.cpp):

#include <iostream>

using namespace std;

int main() {
    cout << "hello world\n";
    return 0;
}

Then, create your CMakeLists.txt file with nothing but just a standard set of commands (~/dev/project/CMakeLists.txt):

cmake_minimum_required(VERSION 3.5)
project(cpptest)
add_executable(cpptest test.cpp)

Next step is to create your build directory:

$ cd ~/dev/project
$ ls
CMakeLists.txt test.cpp
$ mkdir build && cd build
$ cmake ..
-- The C compiler identification is GNU 8.2.1
-- The CXX compiler identification is GNU 8.2.1
-- Check for working C compiler: /bin/cc
-- Check for working C compiler: /bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /bin/c++
-- Check for working CXX compiler: /bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/antek/dev/project/build

Now you can issue make in order to build the project, but also you can do:

$ make test.cpp.i
Preprocessing CXX source to CMakeFiles/cpptest.dir/test.cpp.i

This way CMake will use proper build flags, include directories, proper dependency management, etc, when generating the preprocessed source file. This should work in your own CMake-based project without any modifications.

G.