Is SPDLOG_COMPILED_LIB required when using the non header-only version?

[deaklajos]

I would like to use the non header only version of spdlog to reduce my build times(mostly template instantiations of spdlog::pattern_formatter::handle_flag_<>).
Tried to use:

target_link_libraries(${EXECUTABLE_NAME} PRIVATE spdlog::spdlog)

instead of

target_link_libraries(${EXECUTABLE_NAME} PRIVATE spdlog::spdlog_header_only)

It didn't do seemingly anything until i added:

target_compile_definitions(${EXECUTABLE_NAME} PRIVATE SPDLOG_COMPILED_LIB)

Am I missing something?
From INSTALL I assumed SPDLOG_COMPILED_LIB is
only needed if I copy the .cpp files to my build tree(bit confusing).
Also as an example in tests/CMakeLists.txt I would assume(from my experince) that target spdlog-utests will use header only even if is linked with spdlog::spdlog.

[tt4g]

Yes. If SPDLOG_COMPILED_LIB is not defined, spdlog will behave as a header-only library.

From INSTALL I assumed SPDLOG_COMPILED_LIB is
only needed if I copy the .cpp files to my build tree(bit confusing).

Not strictly true.
You need to import spdlog into your CMake project before add_target_link_libraries().

There are several ways to do this.
If spdlog is installed on your machine, you can use find_package().
This method is also used in tests.

spdlog/tests/CMakeLists.txt

Line 6 in 8fed530

find_package(spdlog REQUIRED)

You can also use FetchContent and add_subdirectory() to import spdlogs.
Please read the CMake documentation for their features.

[deaklajos]

Yes. If SPDLOG_COMPILED_LIB is not defined, spdlog will behave as a header-only library.

Then shouldn't spdlog-utests compiled with SPDLOG_COMPILED_LIB?
And

spdlog/INSTALL

Lines 14 to 15 in 8fed530

	add_executable(example example.cpp)
	target_link_libraries(example spdlog::spdlog)

Be

add_executable(example example.cpp)
target_link_libraries(example spdlog::spdlog)
target_compile_definitions(example SPDLOG_COMPILED_LIB)

[tt4g]

No, that is not necessary.
Using spdlog found by find_package() automatically defines the macros defined in CMakeLists.txt in spdlog for the associated application.

CMake target spdlog (spdlog::spdlog is alias of spdlog) is a compiled library, so SPDLOG_COMPILED_LIB is defined in example target.

spdlog/CMakeLists.txt

Line 173 in 8fed530

add_library(spdlog::spdlog ALIAS spdlog)

spdlog/CMakeLists.txt

Line 180 in 8fed530

target_compile_definitions(spdlog PUBLIC SPDLOG_COMPILED_LIB)

This is a CMake feature, so please learn more about CMake.

[deaklajos]

Thanks, I didn't know that it would propagate definitions like that.
The problem was on our side, for every translation unit we created object libraries and in the end we link them together into an executable and only that time we linked spdlog.
I guess we should be linking every dependency to those object libs as well.

[tt4g]

Yes, all projects that reference the spdlog header file should have the same macros defined as when spdlog was built.