Recursive CMake search for header and source files

My answer is mostly a hack, but I find it useful if you don't want to add all dir manually.

This macro will recursively scan all sub-directories (and their sub-directories, etc ...). If a directory contains a header (.h) file, it will append its path to the return_list. This list can then be used with target_include_directories.

MACRO(HEADER_DIRECTORIES return_list)
    FILE(GLOB_RECURSE new_list *.h)
    SET(dir_list "")
    FOREACH(file_path ${new_list})
        GET_FILENAME_COMPONENT(dir_path ${file_path} PATH)
        SET(dir_list ${dir_list} ${dir_path})
    ENDFOREACH()
    LIST(REMOVE_DUPLICATES dir_list)
    SET(${return_list} ${dir_list})
ENDMACRO()

Usage:

HEADER_DIRECTORIES(header_dir_list)

list(LENGTH header_dir_list header_dir_list_count)
message(STATUS "[INFO] Found ${header_dir_list_count} header directories.")

target_include_directories(
    my_program
    PUBLIC
    ${header_dir_list} # Recursive
)

Macro credit: Christoph

Tested with Cmake 3.10

You're probably missing one or more include_directories calls. Adding headers to the list of files in the add_executable call doesn't actually add then to the compiler's search path - it's a convenience feature whereby they are only added to the project's folder structure in IDEs.

So, in your root, say you have /my_lib/foo.h, and you want to include that in a source file as

#include "my_lib/foo.h"

Then in your CMakeLists.txt, you need to do:

include_directories(${CMAKE_SOURCE_DIR})

If, instead you just want to do

#include "foo.h"

then in the CMakeLists.txt, do

include_directories(${CMAKE_SOURCE_DIR}/my_lib)

I should mention that file(GLOB...) is not the recommended way to gather your list of sources - you should really just add each file explicitly in the CMakeLists.txt. By doing this, if you add or remove a source file later, the CMakeLists.txt is modified, and CMake automatically reruns the next time you try and build. From the docs for file:

We do not recommend using GLOB to collect a list of source files from your source tree. If no CMakeLists.txt file changes when a source is added or removed then the generated build system cannot know when to ask CMake to regenerate.