CMake -- Add all sources in subdirectory to cmake project - c++

Question

As a follow up to this question:
Add Source in a subdirectory to a cmake project
What is the best way (perhaps using the FILE directive?) to select all the .cpp and .h files in the subdirectory and add them to the SOURCE variable defined in the parent directory?
Example from answer to question above:
set(SOURCE
${SOURCE}
${CMAKE_CURRENT_SOURCE_DIR}/file1.cpp
${CMAKE_CURRENT_SOURCE_DIR}/file2.cpp
PARENT_SCOPE
)
set(HEADERS
${HEADERS}
${CMAKE_CURRENT_SOURCE_DIR}/file1.hpp
${CMAKE_CURRENT_SOURCE_DIR}/file2.hpp
PARENT_SCOPE
)
Is it possible to do something like this?
FILE(GLOB SUB_SOURCES *.cpp)
set(SOURCE
${SOURCE}
${CMAKE_CURRENT_SOURCE_DIR}/${SUB_SOURCES}
PARENT_SCOPE
)
What is the best way (using CMake) to compile all the sources in a directory and a subdirectory into a single output file (not multiple libraries?)

Answer 1

I think what you are looking for is the aux_source_directory command.
aux_source_directory Find all source files in a directory.
aux_source_directory( )
Collects the names of all the source files in the specified directory
and stores the list in the provided. This command is
intended to be used by projects that use explicit template
instantiation. Template instantiation files can be stored in a
"Templates" subdirectory and collected automatically using this
command to avoid manually listing all instantiations.
It is tempting to use this command to avoid writing the list of source
files for a library or executable target. While this seems to work,
there is no way for CMake to generate a build system that knows when a
new source file has been added. Normally the generated build system
knows when it needs to rerun CMake because the CMakeLists.txt file is
modified to add a new source. When the source is just added to the
directory without modifying this file, one would have to manually
rerun CMake to generate a build system incorporating the new file.
Your CMakeLists.txt within the subdirectory could look like this:
aux_source_directory(${CMAKE_CURRENT_SOURCE_DIR} SUB_SOURCES)
set(SOURCE
${SOURCE}
${SUB_SOURCES}
PARENT_SCOPE
)
The recommended practice is however, as you see from the documentation, to list the files individually within CMakeLists.txt as changes to the CMakeLists.txt file triggers running cmake.
I hope this was helpful and to the point.