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handle C++ and C string formatting, output, dates, and ranges with type-safe format strings and portable performance

OSS scale score 307.8OSS health 85Update pace 60 commits/30d
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Stars
25,864
Primary language
C++
License
MIT
Repository last updated
Oct 3, 2026
On this page

Overview

{fmt} is a C++ formatting library built around APIs such as fmt::format and fmt::print. Its API family influenced C++20 std::format and C++23 std::print, and it extends to dates, ranges, styled output, and user-defined types.

Features and best fit

Based on official documentation; not hands-on tested · Content checked:

Key features

Build strings and output through type-safe fmt::format and fmt::print

Python-like format-string syntax supports positional arguments and format specifiers while keeping formatting tied to C++ types. With C++20, invalid format specifiers can be diagnosed at compile time.

Sources: [1]

Format dates, ranges, styled text, and user-defined types

Headers such as fmt/chrono.h, fmt/ranges.h, and fmt/color.h extend the same formatting model to dates, containers, and text styles, while custom formatters integrate user-defined types.

Sources: [1]

Choose header-only, CMake library, C11 API, or C++20 module integration

The library can be compiled normally or used with FMT_HEADER_ONLY. Version 12.2.0 also adds the C11 fmt-c API and a fmt::fmt-module target for C++20 modules.

Sources: [1][2][3]

Best fit

Fits C++ codebases replacing printf or iostreams with consistent cross-platform formatting

It is useful when type safety, portable Unicode handling, formatting extensibility, and compile-time checking should be shared across applications and libraries.

Sources: [1]

Before adoption

Treat upstream benchmark numbers as workload-specific

The upstream README publishes performance comparisons against printf and iostreams, but results depend on compiler, optimization settings, and data patterns. Performance-driven adoption should be measured against the real application workload.

Sources: [1]

Review deprecated APIs and include changes in 12.2.0

Version 12.2.0 removes fmt::say, deprecates some fmt::join and related overloads, and changes <fmt/core.h> so it no longer implicitly provides all of <fmt/format.h> unless compatibility is requested.

Sources: [2]

Official sources

  1. [1]{fmt} 12.2.0 README(2026-10-04)
  2. [2]{fmt} 12.2.0 release(2026-10-04)
  3. [3]{fmt} 12.2.0 CMake configuration(2026-10-04)
  4. [4]{fmt} MIT license(2026-10-04)
Supplemental curator note

{fmt} is more than a printf replacement when a codebase needs type-safe format strings and consistent output rules across platforms. Evaluate real workload performance together with compile time and binary-size tradeoffs rather than relying only on published benchmarks.

Try it in 3 steps

  1. 1

    Fetch the {fmt} 12.2.0 source

    Pin the checkout to the reviewed latest release tag.

    git clone --depth 1 --branch 12.2.0 https://github.com/fmtlib/fmt.git fmt-12.2.0
  2. 2

    Build the library with CMake

    Build the compiled library with documentation and tests disabled. The CMake configuration requests the C++11 compile feature.

    cmake -S fmt-12.2.0 -B fmt-12.2.0/build -DFMT_TEST=OFF -DFMT_DOC=OFF && cmake --build fmt-12.2.0/build --config Release
  3. 3

    Compile and run a minimal fmt::print program

    This is a Unix-like toolchain example. answer=42 confirms basic formatting and linking. On Windows, link the generated CMake target from Visual Studio instead.

    cd fmt-12.2.0 && printf '#include <fmt/base.h>\nint main() { fmt::print("answer={}\\n", 42); }\n' > demo.cc && c++ -std=c++11 demo.cc -Iinclude build/libfmt.a -o demo && ./demo
Check the official README

Growth

Growth trends · Last 30 days

25,864 Stars

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Development activity

Last 90 days · weekly

Commits (last 30 days)
60
Open PRs
6

Development activity is still being collected.

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GitHub data

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GitHub Topics

  • formatting
  • printf
  • output
  • chrono
  • performance
  • multiplatform
  • cross-platform
  • cpp
  • ranges
  • floating-point
  • unicode
  • c-plus-plus
Stars
25,864
Forks
3,079
Watchers
326
Open issues
6
Contributors
436
Owner type
Organization
Primary language
C++
License
MIT
Repository last updated
Oct 3, 2026
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