1--- 2hide: 3 - navigation 4 - toc 5--- 6 7# A modern formatting library 8 9<div class="features-container"> 10 11<div class="feature"> 12<h2>Safety</h2> 13<p> 14 Inspired by Python's formatting facility, {fmt} provides a safe replacement 15 for the <code>printf</code> family of functions. Errors in format strings, 16 which are a common source of vulnerabilities in C, are <b>reported at 17 compile time</b>. For example: 18 19 <pre><code class="language-cpp" 20 >fmt::format("{:d}", "I am not a number");</code></pre> 21 22 will give a compile-time error because <code>d</code> is not a valid 23 format specifier for strings. APIs like <a href="api/#format"> 24 <code>fmt::format</code></a> <b>prevent buffer overflow errors</b> via 25 automatic memory management. 26</p> 27<a href="api#compile-time-checks">→ Learn more</a> 28</div> 29 30<div class="feature"> 31<h2>Extensibility</h2> 32<p> 33 Formatting of most <b>standard types</b>, including all containers, dates, 34 and times is <b>supported out-of-the-box</b>. For example: 35 36 <pre><code class="language-cpp" 37 >fmt::print("{}", std::vector{1, 2, 3});</code></pre> 38 39 prints the vector in a JSON-like format: 40 41 <pre><code>[1, 2, 3]</code></pre> 42 43 You can <b>make your own types formattable</b> and even make compile-time 44 checks work for them. 45</p> 46<a href="api#udt">→ Learn more</a> 47</div> 48 49<div class="feature"> 50<h2>Performance</h2> 51<p> 52 {fmt} can be anywhere from <b>tens of percent to 20-30 times faster</b> than 53 iostreams and <code>sprintf</code>, especially for numeric formatting. 54 55<a href="https://github.com/fmtlib/fmt?tab=readme-ov-file#benchmarks"> 56<img src="perf.svg"> 57</a> 58 59 The library <b>minimizes dynamic memory allocations</b> and can optionally 60 <a href="api#compile-api">compile format strings</a> to optimal code. 61</p> 62</div> 63 64<div class="feature"> 65<h2>Unicode support</h2> 66<p> 67 {fmt} provides <b>portable Unicode support</b> on major operating systems 68 with UTF-8 and <code>char</code> strings. For example: 69 70 <pre><code class="language-cpp" 71 >fmt::print("Слава Україні!");</code></pre> 72 73 will be printed correctly on Linux, macOS, and even Windows console, 74 irrespective of the codepages. 75</p> 76<p> 77 The default is <b>locale-independent</b>, but you can opt into localized 78 formatting and {fmt} makes it work with Unicode, addressing issues in the 79 standard libary. 80</p> 81</div> 82 83<div class="feature"> 84<h2>Fast compilation</h2> 85<p> 86 The library makes extensive use of <b>type erasure</b> to achieve fast 87 compilation. <code>fmt/base.h</code> provides a subset of the API with 88 <b>minimal include dependencies</b> and enough functionality to replace 89 all uses of <code>*printf</code>. 90</p> 91<p> 92 Code using {fmt} is usually several times faster to compile than the 93 equivalent iostreams code, and while <code>printf</code> compiles faster 94 still, the gap is narrowing. 95</p> 96<a href= 97"https://github.com/fmtlib/fmt?tab=readme-ov-file#compile-time-and-code-bloat"> 98→ Learn more</a> 99</div> 100 101<div class="feature"> 102<h2>Small binary footprint</h2> 103<p> 104 Type erasure is also used to prevent template bloat, resulting in <b>compact 105 per-call binary code</b>. For example, a call to <code>fmt::print</code> with 106 a single argument is just <a href="https://godbolt.org/g/TZU4KF">a few 107 instructions</a>, comparable to <code>printf</code> despite adding 108 runtime safety, and much smaller than the equivalent iostreams code. 109</p> 110<p> 111 The library itself has small binary footprint and some components such as 112 floating-point formatting can be disabled to make it even smaller for 113 resource-constrained devices. 114</p> 115</div> 116 117<div class="feature"> 118<h2>Portability</h2> 119<p> 120 {fmt} has a <b>small self-contained codebase</b> with the core consisting of 121 just three headers and no external dependencies. 122</p> 123<p> 124 The library is highly portable and requires only a minimal <b>subset of 125 C++11</b> features which are available in GCC 4.9, Clang 3.4, MSVC 19.0 126 (2015) and later. Newer compiler and standard library features are used 127 if available, and enable additional functionality. 128</p> 129<p> 130 Where possible, the output of formatting functions is <b>consistent across 131 platforms</b>. 132</p> 133</p> 134</div> 135 136<div class="feature"> 137<h2>Open source</h2> 138<p> 139 {fmt} is in the top hundred open-source C++ libraries on GitHub and has 140 <a href="https://github.com/fmtlib/fmt/graphs/contributors">hundreds of 141 all-time contributors</a>. 142</p> 143<p> 144 The library is distributed under a permissive MIT 145 <a href="https://github.com/fmtlib/fmt#license">license</a> and is 146 <b>relied upon by many open-source projects</b>, including Blender, PyTorch, 147 Apple's FoundationDB, Windows Terminal, MongoDB, and others. 148</p> 149</div> 150 151</div> 152
