how to use CMake file (GLOB SRCS *. ) with a build directory - cmake

Question

this is my current CMakeLists.txt file
cmake_minimum_required(VERSION 3.3)
set(CMAKE_C_FLAGS " -Wall -g ")
project( bmi )
file( GLOB SRCS *.cpp *.h )
add_executable( bmi ${SRCS})
This builds from my source directory, but I have to clean up all the extra files after. My question is how do I build this from a build directory if all my source files are in the same source directory?
thanks

Answer 1

If you really need to use file(GLOB …), this CMakeLists.txt should work :
cmake_minimum_required(VERSION 3.3)
project(bmi)
add_definitions("-Wall" "-g")
include_directories(${PROJECT_SOURCE_DIR})
file(GLOB SRC_FILES ${PROJECT_SOURCE_DIR}/*.cpp)
add_executable(bmi ${SRC_FILES})
In this case you have to launch cmake from your build directory every time you add or delete a source file :
cmake <your_source_dir> -G <your_build_generator>
As Phil reminds, CMake documentation doesn't recommend this use of GLOB. But there are some exceptions. You'll get more information on this post.
If you don't meet those exceptions, you'd rather list your source files than use GLOB :
set(SRC_FILES ${PROJECT_SOURCE_DIR}/main.cpp
${PROJECT_SOURCE_DIR}/bmi.cpp
… )
NB : if you have #include of your .h files in .cpp files, I don't see any reason to put them in add_executable, you just need to specify include directory with include_directories.

Answer 2

Cmake used to only update the list of source files if CMakeLists.txt was changed since the last cmake run or if cmake was used to configure the project again.
In cmake 3.11.0 recursive search and automatic re-configuration on adding or deleting source files was added. Since then you can use the following snippet:
if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.11.0")
file(GLOB_RECURSE SOURCE_FILES CONFIGURE_DEPENDS *.cpp *.h)
else()
file(GLOB SOURCE_FILES *.cpp *.h */*.h */*.cpp)
endif()
The file() command after the else() provides at least a bit of backwards compatibility: It still searches for source files in the current folder and its direct subfolders. But it doesn't automatically recognize if there are new files or old files have been deleted.
Note that VERSION_GREATER_EQUAL is only available in cmake >= 3.7