Honey, I shrunk {fmt}: bringing binary size to 14k and ditching the C++ runtime
The {fmt} formatting library is known for its small binary footprint, often producing code that is several times smaller per function call compared to alternatives like IOStreams, Boost Format, or, somewhat ironically, tinyformat. This is mainly achieved through careful application of type erasure on various levels, which effectively minimizes template bloat.
This approach confines template usage to a minimal top-level layer, leading to both a smaller binary size and faster build times.
Unlike printf, {fmt} offers full runtime type safety. Errors in format strings can be caught at compile time, and even when the format string is determined at runtime, errors are managed through exceptions, preventing undefined behavior, memory corruption, and potential crashes. Additionally, {fmt} calls are generally more efficient, particularly when using positional arguments, which C varargs are not well-suited for.
Back in 2020, I dedicated some time to optimizing the library size, successfully reducing it to under 100kB (just ~57kB with -Os -flto). A lot has changed since then. Most notably, {fmt} now uses the exceptional Dragonbox algorithm for floating-point formatting, kindly contributed by its author, Junekey Jeon. Let’s explore how these changes have impacted the binary size and see if further reductions are possible.
