CMake: add compile flag for header only library

Question

Unsure about how to use CMake properly here. I have one library, which is a template header only library which uses C++20 features. Therefore, I want to make sure that any [downstream/consumer/dependent] of my library compiles the specialization of my library with the correct flags.

First lib does the following:

add_library(foo INTERFACE include/foo.h)

Now, foo uses the filesystem stuff from c++20, so I want to do something like this:

target_compile_features(foo INTERFACE cxx_std_20)
target_link_libraries(foo INTERFACE stdc++fs)

In my dependent, I then want to do

add_executable(bar src/bar.cpp)
find_package(foo REQUIRED)
target_link_libraries(bar foo)

// src/bar.cpp
#include "foo.h" // or something like that

Currently, linker fails. What's the proper way to set this up?

Where does your find/package configuration script come from. A handmade one containing the first 2 lines in combination with the appropliate `target_include_directories` command should be working... — fabian, Aug 04 '22 at 17:48

score 1 · Accepted Answer · edited Aug 04 '22 at 17:47

1

target_link_libraries is to set libraries to link with when actually building the specified target. The problem here is that INTERFACE libraries aren't built.

You need to add the libraries to link with as a dependency for your library.

This is done with the set_target_properties command to set the INTERFACE_LINK_LIBRARIES property:

set_target_properties(foo
    PROPERTIES INTERFACE_LINK_LIBRARIES stdc++fs)

edited Aug 04 '22 at 17:47

fabian

80,457
12
86
114

answered Aug 04 '22 at 11:25

Some programmer dude

400,186
35
402
621

Thank you. Can I add a C++20 flag to this interface as well? Or is that superfluous? – user93114 Aug 04 '22 at 11:53
1

@user93114 `target_compile_features` should work as you intend, I think. It should set the [`INTERFACE_COMPILE_FEATURES`](https://cmake.org/cmake/help/latest/prop_tgt/INTERFACE_COMPILE_FEATURES.html) property. – Some programmer dude Aug 04 '22 at 11:56
@user93114 To check you can do a verbose build where the commands are shown with all flags and options. – Some programmer dude Aug 04 '22 at 11:57

CMake: add compile flag for header only library

1 Answers1