Deciding what to write in CMakeLists.txt - mainly in subfolders - c++

Question

I have a simple project going that uses CMake and gtest. I have a basic CMakeLists.txt file working, but I want to get a better understanding of how to use multiple CMakeLists.txt's and connect them. The code so far for the project is like this:
https://github.com/dmonopoly/writeart/tree/10b62048e6eb6a6ddd0658123d85ce4f5f601178
For quicker reference, the only CMakeLists.txt file (in the project root) that I take advantage of has this inside:
cmake_minimum_required(VERSION 2.8)
# Options
option(TEST "Build all tests." OFF) # makes boolean 'TEST' available
# Make PROJECT_SOURCE_DIR, PROJECT_BINARY_DIR, and PROJECT_NAME available
set(PROJECT_NAME MyProject)
project(${PROJECT_NAME})
set(CMAKE_CXX_FLAGS "-g") # -Wall")
#set(COMMON_INCLUDES ${PROJECT_SOURCE_DIR}/include) if you want your own include/ directory
# then you can do include_directories(${COMMON_INCLUDES}) in other cmakelists.txt files
################################
# Normal Libraries & Executables
################################
add_library(standard_lib Standard.cpp Standard.h)
add_library(converter_lib Converter.cpp Converter.h)
add_executable(main Main.cpp)
target_link_libraries(main standard_lib converter_lib)
################################
# Testing
################################
if (TEST)
# This adds another subdirectory, which has project(gtest)
add_subdirectory(lib/gtest-1.6.0)
enable_testing()
# Include the gtest library
# gtest_SOURCE_DIR is available due to project(gtest) above
include_directories(${gtest_SOURCE_DIR}/include ${gtest_SOURCE_DIR})
##############
# Unit Tests
##############
# Naming
set(UNIT_TESTS runUnitTests)
add_executable(${UNIT_TESTS} ConverterTest.cpp)
# standard linking to gtest stuff
target_link_libraries(${UNIT_TESTS} gtest gtest_main)
# extra linking for the project
target_link_libraries(${UNIT_TESTS} standard_lib converter_lib)
# This is so you can do 'make test' to see all your tests run, instead of manually running the executable runUnitTests to see those specific tests.
add_test(NAME myUnitTests COMMAND runUnitTests)
endif()
My goal is to move Standard.cpp and Standard.h into lib/. The moment I do this, though, I find the ordering of what I do in my CMakeLists.txt complicated. I need the library for my gtest setup, but the library would have to get made in lib/CMakeLists.txt, right? Wouldn't it easily become really complicated to find where all your libraries are and executables are as you would have to look through all your CMakeLists.txt's?
If I am missing something conceptually, or if there is a good example I could use to solve this easily, that would be great.
Help appreciated, and thanks in advance.

Answer 1

If you don't want to use multiple CMakeLists.txt files, don't.
################################
# Normal Libraries & Executables
################################
add_library(standard_lib lib/Standard.cpp lib/Standard.h)
add_library(converter_lib lib/Converter.cpp lib/Converter.h)
# Main.cpp needs to know where "Standard.h" is for the #include,
# so we tell it to search this directory too.
include_directories(lib)
If you do want multiple CMakeLists.txt, you'd move it out:
# Main CMakeLists.txt:
add_subdirectory(lib)
include_directories (${standard_lib_SOURCE_DIR}/standard_lib)
link_directories (${standard_lib_BINARY_DIR}/standard_lib)
and in /lib/CMakeLists.txt:
add_library (standard_lib Standard.cpp)
Here's an example.