Usage of spdlog with fmt

[copilot0058]

Install the spdlog with fmt, then I try to find_package(SPDLOG)

it show the error, but I alread install the spdlog with fmt.
Why does it still need twice?
one is cmake build spdlog with fmt, another is use find_package(SPDLOG) on project.

the error is find_package(SPDLOG), by the way, I already install the spdlog with fmt

> [CMake] CMake Error at C:/Program Files/Microsoft Visual Studio/2022/Community/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/share/cmake-3.28/Modules/CMakeFindDependencyMacro.cmake:76 (find_package):
1> [CMake]   Could not find a package configuration file provided by "fmt" with any of
1> [CMake]   the following names:
1> [CMake] 
1> [CMake]     fmtConfig.cmake
1> [CMake]     fmt-config.cmake
1> [CMake] 
1> [CMake]   Add the installation prefix of "fmt" to CMAKE_PREFIX_PATH or set "fmt_DIR"
1> [CMake]   to a directory containing one of the above files.  If "fmt" provides a
1> [CMake]   separate development package or SDK, be sure it has been installed.

spdlog/CMakeLists.txt

Line 91 in 2c76e61

option(SPDLOG_FMT_EXTERNAL "Use external fmt library instead of bundled" OFF)

https://github.com/gabime/spdlog/blob/v1.x/example/CMakeLists.txt

[tt4g]

fmt is not always installed with spdlog.
And, it is the bundled fmt (header files) that is installed, not fmt.dll.

spdlog/CMakeLists.txt

Lines 322 to 325 in 2c76e61

	if(NOT SPDLOG_USE_STD_FORMAT AND NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
	install(DIRECTORY include/${PROJECT_NAME}/fmt/bundled/
	DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}/fmt/bundled/")
	endif()

If you installed spdlog with SPDLOG_FMT_EXTERNAL=ON, you are responsible for installing fmt on your machine.

[copilot0058]

I want to clarify: I have already installed fmt and spdlog, and I have set SPDLOG_FMT_EXTERNAL=ON.
Now I want to use the already compiled spdlog (with fmt) in my own project.
Therefore, I used find_package(SPDLOG). Since I have already compiled spdlog (with fmt), I shouldn't need the fmt config, right?

Here is the compiled spdlog

C:.
├─include
│  └─spdlog
│      ├─cfg
│      ├─details
│      ├─fmt
│      └─sinks
└─lib
    ├─spdlog.lib
    ├─cmake
    │  └─spdlog
    └─pkgconfig

[tt4g]

If C:\lib\fmt.lib is missing, fmt is not installed.
You must download the source code from the fmt project and install fmt.
Then, spdlog must be rebuilt to reference the installed fmt.

[copilot0058]

If I want to build spdlog with fmt and only use find_package(SPDLOG) on my project. (no find_package(fmt) on my project )
how can I set the cmake option?

[tt4g]

Rebuild and reinstall spdlog without defining SPDLOG_FMT_EXTERNAL.

[copilot0058]

Thanks,

So the default setting is using include/spdlog/fmt ?

https://github.com/gabime/spdlog/tree/v1.x/include/spdlog/fmt

SPDLOG_FMT_EXTERNAL=OFF     ====>      using include/spdlog/fmt of spdlog 
SPDLOG_FMT_EXTERNAL=ON      ====>      using external fmt

[tt4g]

include/spdlog/fmt is a header file for spdlog to use fmt and std::format separately.
Bundled fmt is include/spdlog/fmt/bundled.