Installation and integration

The header-only default is what makes spdlog trivial to adopt — copy a directory, add an include path, done. It's also what makes a large project's incremental compile times worse, because every translation unit that includes spdlog.h re-parses (and re-instantiates) all of it. The compiled mode exists for exactly that trade-off.

Header-only

Copy or vendor the include/spdlog directory into your project, add it to your include path, and you're done:

#include "spdlog/spdlog.h"

No linking, no build step. This is the right default for small projects, examples, and anything where compile time isn't yet a problem.

Compiled mode

Define SPDLOG_COMPILED_LIB and build spdlog as a static or shared library instead. In CMake terms that's the difference between linking against the spdlog::spdlog target (compiled) and spdlog::spdlog_header_only (header-only) — both are provided by the project's CMake config.

What compiled mode buys you: each translation unit only sees declarations, not the full implementation, so incremental builds get noticeably faster once you have more than a handful of files including spdlog. What it costs: an actual build/link step, and an ABI contract between the compiled library and your code (same compiler, same standard library, same SPDLOG_ACTIVE_LEVEL — see Compile-time log level).

CMake: find_package

If spdlog is installed on the system (via a package manager or cmake --install):

CMakeLists.txt

find_package(spdlog REQUIRED)

add_executable(app main.cpp)
target_link_libraries(app PRIVATE spdlog::spdlog)   # compiled
# target_link_libraries(app PRIVATE spdlog::spdlog_header_only)  # header-only

CMake: FetchContent

When you don't want to assume spdlog is installed, pull it in at configure time:

CMakeLists.txt

include(FetchContent)
FetchContent_Declare(
    spdlog
    GIT_REPOSITORY https://github.com/gabime/spdlog.git
    GIT_TAG v1.14.1
)
FetchContent_MakeAvailable(spdlog)

target_link_libraries(app PRIVATE spdlog::spdlog)

See FetchContent for the general mechanism this builds on.

vcpkg and Conan

vcpkg install spdlog

conan install spdlog/1.14.1@

Both packages expose the same spdlog::spdlog / spdlog::spdlog_header_only targets, so the find_package block above doesn't change regardless of which one provided the package.

The bundled fmt

spdlog vendors a copy of fmt by default (spdlog/fmt/bundled/), so you don't need a separate fmt install to get started. Define SPDLOG_FMT_EXTERNAL to use your own fmt installation instead — useful when another dependency in your project already pulls in fmt and you want one copy, not two.

Mixing a vendored fmt and an external fmt in one binary causes ODR violations

If one translation unit links against spdlog's bundled fmt and another links against a system fmt, you can end up with two different definitions of the same fmt symbols in one binary. Pick one mode (SPDLOG_FMT_EXTERNAL or not) and apply it consistently across every target that touches spdlog.

Which mode should I use?

	Header-only	Compiled lib
Compile time	Slower per TU, no link step	Faster per TU, one link step
Distribution	Copy headers, nothing to build	Ship or build a .a/.so/.lib
ABI	N/A — always recompiled together	Must match compiler/stdlib/SPDLOG_ACTIVE_LEVEL
Best for	Small projects, quick integration	Large projects, many TUs including spdlog

Start header-only, switch when compile time hurts

There's no reason to reach for compiled mode on day one. Switch when spdlog.h shows up meaningfully in your build-time profile.

See also

• What is spdlog? — the architecture these install modes plug into.
• Quick start — first program once it's installed.
• find_package — the general CMake mechanism used above.
• FetchContent — pulling in a dependency without a system install.
• spdlog overview.