The `fmtlib/fmt` repository provides a modern, high-performance, and safe formatting library for C++. Its primary purpose is to offer a superior alternative to the standard C `stdio` and C++ `iostreams` libraries, addressing their limitations in terms of speed, safety, and ease of use. The library is designed to be a drop-in replacement for common formatting tasks, offering a more streamlined and efficient approach.

The core functionality of {fmt} revolves around its flexible and intuitive format API. It supports a format string syntax that closely resembles Python's, making it easy to learn and use. A key feature is the inclusion of positional arguments, crucial for internationalization (i18n) and localization. This allows for reordering arguments in the output string, enhancing flexibility and code maintainability. The library also implements C++20 `std::format` and C++23 `std::print`, ensuring compatibility with the latest C++ standards.

A significant advantage of {fmt} is its performance. Benchmarks consistently demonstrate that it is faster than common standard library implementations of `printf`, iostreams, `to_string`, and `to_chars`. This performance boost is achieved through optimized algorithms, including a fast IEEE 754 floating-point formatter utilizing the Dragonbox algorithm, which guarantees correct rounding, shortness, and round-trip accuracy. The library's speed is particularly noticeable in tasks involving string conversion from integers and floating-point numbers.

Beyond speed, {fmt} prioritizes safety and reliability. It is fully type-safe, with compile-time error checking for format strings, preventing potential runtime issues. The library's design incorporates automatic memory management, mitigating the risk of buffer overflow errors. Extensive testing and continuous fuzzing through OSS-Fuzz contribute to its robustness. The codebase is also designed to be clean and warning-free, even with high compiler warning levels.

{fmt} offers several other notable features. It provides portable Unicode support, ensuring consistent output across different platforms. It includes a safe `printf` implementation, including the POSIX extension for positional arguments. The library is also extensible, allowing users to define custom formatting for their own types. The code size is kept small, with a minimal configuration consisting of just three files. The library is header-only configurable, making it easy to integrate into projects.

The repository includes comprehensive documentation, examples, and benchmarks to facilitate understanding and usage. The documentation covers the format API, syntax, and portability aspects. The examples demonstrate how to print to standard output, format strings, use positional arguments, print dates and times, print containers, and utilize compile-time format string checking. The benchmarks compare {fmt} against other formatting methods, highlighting its performance advantages.

The repository also provides information on migrating existing code to use {fmt}, including guidance on using clang-tidy for automated conversion from `printf` and `fprintf`. A list of notable projects using the library is provided, showcasing its widespread adoption in various domains, including game development, database systems, and machine learning. The repository also details the motivation behind creating {fmt}, explaining the shortcomings of existing formatting solutions and highlighting the advantages of the library's design. The project is licensed under the permissive MIT license, making it suitable for a wide range of projects.