fmt: Format C++ Text Safely and Efficiently

Overview

{fmt} is a C++ library for formatting values into strings and writing formatted output. It offers an alternative to C stdio and iostreams, with a Python-like format syntax and type-safe argument handling.

It is useful when an application needs consistent formatting across platforms, support for custom types, or control over formatting performance and compile-time checks. The project also implements C++20 std::format and C++23 std::print interfaces.

Key Features

• Format strings and print output using positional or automatic arguments.
• Support for compile-time format-string checks in C++20.
• Format numbers, dates, times, ranges, Unicode text, colors, and user-defined types.
• Provide a safe printf-style API, including positional arguments.
• Offer an optional header-only configuration with FMT_HEADER_ONLY.
• Include tests and continuous fuzzing, according to the project README.

Use Cases

• C++ application developers can use it to format strings and console output with type-checked arguments.
• Library authors can add formatting support for custom types through the extension API.
• Teams targeting multiple platforms can use it for consistent formatting behavior and Unicode support.
• Performance-sensitive applications can evaluate it as an alternative to iostreams or stdio for formatting workloads.
• Projects that want to adopt familiar standard formatting interfaces can use its std::format and std::print implementations.

Project Facts

• Language: C++
• License: MIT
• Stars: 25.9k
• Forks: 3.1k
• Topics: c-plus-plus, chrono, cpp, cross-platform, floating-point, formatting, multiplatform, output, performance, printf, ranges, unicode
• Archived: No

Getting Started

See the README and documentation for installation and build instructions. A basic example is:

#include <fmt/core.h>

int main() {
  fmt::print("Hello, world!\n");
}

Considerations

• This is a C++ library, so using it requires a C++ project and a compatible compiler. The README describes support for older compilers but does not list requirements here.
• Header-only use is optional. Projects can instead build and link the library.
• Performance depends on the workload and environment. Consult the linked benchmarks and methodology before choosing it on performance grounds.