CMake #include path relative to project root [duplicate] - c++

Question

I have set up a CMake project whose directory structure looks as follows:
src/
--CMakeLists.txt
--libA/
----CMakeLists.txt
----foo.h
----foo.cpp
--main/
----CMakeLists.txt
----main.cpp
src/CMakeLists.txt uses add_subdirectory to pull in libA and main. libA/CMakeLists.txt uses add_library to define a library called libA, which exports foo.h via target_include_directories. If I now link against libA in main using target_link_library, I can include foo.h via #include <foo.h> in main.cpp.
Question: Is it possible to provide the public interface of libA with a prefix, so that I can (and have to) write #include <libA/foo.h> in main.cpp instead?

Answer 1

This is an old question but I was having exactly the same issue. I ended up getting around this by adding an export_headers() function that creates symbolic links to the headers within the binary:
function(export_headers TARGET HEADER_SOURCE_DIR HEADER_DEST_DIR)
# Put all headers that are in the source directory into EXPORT_HEADERS variable
file(GLOB_RECURSE EXPORT_HEADERS CONFIGURE_DEPENDS
RELATIVE "${HEADER_SOURCE_DIR}"
"${HEADER_SOURCE_DIR}/*.h"
)
# For each header that will be exported
foreach(HEADER ${EXPORT_HEADERS})
# Get the directory portion that needs to be created
get_filename_component(HEADER_DIRECTORY "${HEADER}" DIRECTORY)
# Create the directory
add_custom_command(TARGET ${TARGET} POST_BUILD
COMMAND ${CMAKE_COMMAND} -E make_directory "${HEADER_DEST_DIR}/${HEADER_DIRECTORY}"
)
if (MSVC)
# Make a hard link to the file
add_custom_command(TARGET ${TARGET} POST_BUILD
COMMAND if not exist "${HEADER_DEST_DIR}/${HEADER}" \( mklink /h "${HEADER_DEST_DIR}/${HEADER}" "${HEADER_SOURCE_DIR}/${HEADER}" \)
)
else()
# Make a symbolic link to the file
add_custom_command(TARGET ${TARGET} POST_BUILD
COMMAND ln -sf "${HEADER_SOURCE_DIR}/${HEADER}" "${HEADER_DEST_DIR}/${HEADER}"
)
endif()
endforeach(HEADER)
endfunction()
You would call this with something like:
add_library(libA STATIC ${LIBA_SOURCES}
export_headers(libA ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_BINARY_DIR}/include/libA)
target_include_directories(libA INTERFACE ${CMAKE_CURRENT_BINARY_DIR}/include)
Then, if you link to libA, you will be able to #include <libA/foo.h>.

Answer 2

You can use the root source directory (or some other directory which is a parent to libA) in the target_include_directories() call. This will allow the INTERFACE_INCLUDE_DIRECTORIES target property to be defined with respect to another directory (in this example, the CMAKE_SOURCE_DIR). So it would look something like this:
In libA/CMakeLists.txt:
add_library(libA foo.cpp)
# Define the include files with respect to the directory above this.
target_include_directories(libA PUBLIC ${CMAKE_SOURCE_DIR})
The main/main.cpp file:
#include <iostream>
#include <libA/foo.h>
int main() {
FooClass fooclass;
fooclass.myFunction();
std::cout << "Hello World!" << std::endl;
return 0;
}