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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Documentation - The Zig Programming Language</title>
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</head>
<body>
<header><h1>Zig Language Reference</h1></header>
<div id="main-wrapper">
<div id="navigation">
<nav aria-labelledby="zig-version">
<h2 id="zig-version">Zig Version</h2>
<a href="https://ziglang.org/documentation/0.1.1/">0.1.1</a> |
<a href="https://ziglang.org/documentation/0.2.0/">0.2.0</a> |
<a href="https://ziglang.org/documentation/0.3.0/">0.3.0</a> |
<a href="https://ziglang.org/documentation/0.4.0/">0.4.0</a> |
<a href="https://ziglang.org/documentation/0.5.0/">0.5.0</a> |
<a href="https://ziglang.org/documentation/0.6.0/">0.6.0</a> |
<a href="https://ziglang.org/documentation/0.7.1/">0.7.1</a> |
<a href="https://ziglang.org/documentation/0.8.0/">0.8.0</a> |
master
</nav>
<nav aria-labelledby="table-of-contents">
<h2 id="table-of-contents">Table of Contents</h2>
<ul>
<li><a id="toc-Introduction" href="#Introduction">Introduction</a></li>
<li><a id="toc-Zig-Standard-Library" href="#Zig-Standard-Library">Zig Standard Library</a></li>
<li><a id="toc-Hello-World" href="#Hello-World">Hello World</a></li>
<li><a id="toc-Zig-Test" href="#Zig-Test">Zig Test</a></li>
<li><a id="toc-Comments" href="#Comments">Comments</a>
<ul>
<li><a id="toc-Doc-comments" href="#Doc-comments">Doc comments</a></li>
<li><a id="toc-Top-Level-Doc-Comments" href="#Top-Level-Doc-Comments">Top-Level Doc Comments</a></li>
</ul></li>
<li><a id="toc-Values" href="#Values">Values</a>
<ul>
<li><a id="toc-Primitive-Types" href="#Primitive-Types">Primitive Types</a></li>
<li><a id="toc-Primitive-Values" href="#Primitive-Values">Primitive Values</a></li>
<li><a id="toc-String-Literals-and-Unicode-Code-Point-Literals" href="#String-Literals-and-Unicode-Code-Point-Literals">String Literals and Unicode Code Point Literals</a>
<ul>
<li><a id="toc-Escape-Sequences" href="#Escape-Sequences">Escape Sequences</a></li>
<li><a id="toc-Multiline-String-Literals" href="#Multiline-String-Literals">Multiline String Literals</a></li>
</ul></li>
<li><a id="toc-Assignment" href="#Assignment">Assignment</a>
<ul>
<li><a id="toc-undefined" href="#undefined">undefined</a></li>
</ul></li>
</ul></li>
<li><a id="toc-Variables" href="#Variables">Variables</a>
<ul>
<li><a id="toc-Container-Level-Variables" href="#Container-Level-Variables">Container Level Variables</a></li>
<li><a id="toc-Static-Local-Variables" href="#Static-Local-Variables">Static Local Variables</a></li>
<li><a id="toc-Thread-Local-Variables" href="#Thread-Local-Variables">Thread Local Variables</a></li>
<li><a id="toc-Local-Variables" href="#Local-Variables">Local Variables</a></li>
</ul></li>
<li><a id="toc-Integers" href="#Integers">Integers</a>
<ul>
<li><a id="toc-Integer-Literals" href="#Integer-Literals">Integer Literals</a></li>
<li><a id="toc-Runtime-Integer-Values" href="#Runtime-Integer-Values">Runtime Integer Values</a></li>
</ul></li>
<li><a id="toc-Floats" href="#Floats">Floats</a>
<ul>
<li><a id="toc-Float-Literals" href="#Float-Literals">Float Literals</a></li>
<li><a id="toc-Floating-Point-Operations" href="#Floating-Point-Operations">Floating Point Operations</a></li>
</ul></li>
<li><a id="toc-Operators" href="#Operators">Operators</a>
<ul>
<li><a id="toc-Table-of-Operators" href="#Table-of-Operators">Table of Operators</a></li>
<li><a id="toc-Precedence" href="#Precedence">Precedence</a></li>
</ul></li>
<li><a id="toc-Arrays" href="#Arrays">Arrays</a>
<ul>
<li><a id="toc-Anonymous-List-Literals" href="#Anonymous-List-Literals">Anonymous List Literals</a></li>
<li><a id="toc-Multidimensional-Arrays" href="#Multidimensional-Arrays">Multidimensional Arrays</a></li>
<li><a id="toc-Sentinel-Terminated-Arrays" href="#Sentinel-Terminated-Arrays">Sentinel-Terminated Arrays</a></li>
</ul></li>
<li><a id="toc-Vectors" href="#Vectors">Vectors</a>
<ul>
<li><a id="toc-SIMD" href="#SIMD">SIMD</a></li>
</ul></li>
<li><a id="toc-Pointers" href="#Pointers">Pointers</a>
<ul>
<li><a id="toc-volatile" href="#volatile">volatile</a></li>
<li><a id="toc-Alignment" href="#Alignment">Alignment</a></li>
<li><a id="toc-allowzero" href="#allowzero">allowzero</a></li>
<li><a id="toc-Sentinel-Terminated-Pointers" href="#Sentinel-Terminated-Pointers">Sentinel-Terminated Pointers</a></li>
</ul></li>
<li><a id="toc-Slices" href="#Slices">Slices</a>
<ul>
<li><a id="toc-Sentinel-Terminated-Slices" href="#Sentinel-Terminated-Slices">Sentinel-Terminated Slices</a></li>
</ul></li>
<li><a id="toc-struct" href="#struct">struct</a>
<ul>
<li><a id="toc-Default-Field-Values" href="#Default-Field-Values">Default Field Values</a></li>
<li><a id="toc-extern-struct" href="#extern-struct">extern struct</a></li>
<li><a id="toc-packed-struct" href="#packed-struct">packed struct</a></li>
<li><a id="toc-Struct-Naming" href="#Struct-Naming">Struct Naming</a></li>
<li><a id="toc-Anonymous-Struct-Literals" href="#Anonymous-Struct-Literals">Anonymous Struct Literals</a></li>
</ul></li>
<li><a id="toc-enum" href="#enum">enum</a>
<ul>
<li><a id="toc-extern-enum" href="#extern-enum">extern enum</a></li>
<li><a id="toc-Enum-Literals" href="#Enum-Literals">Enum Literals</a></li>
<li><a id="toc-Non-exhaustive-enum" href="#Non-exhaustive-enum">Non-exhaustive enum</a></li>
</ul></li>
<li><a id="toc-union" href="#union">union</a>
<ul>
<li><a id="toc-Tagged-union" href="#Tagged-union">Tagged union</a></li>
<li><a id="toc-extern-union" href="#extern-union">extern union</a></li>
<li><a id="toc-packed-union" href="#packed-union">packed union</a></li>
<li><a id="toc-Anonymous-Union-Literals" href="#Anonymous-Union-Literals">Anonymous Union Literals</a></li>
</ul></li>
<li><a id="toc-opaque" href="#opaque">opaque</a></li>
<li><a id="toc-blocks" href="#blocks">blocks</a>
<ul>
<li><a id="toc-Shadowing" href="#Shadowing">Shadowing</a></li>
</ul></li>
<li><a id="toc-switch" href="#switch">switch</a>
<ul>
<li><a id="toc-Exhaustive-Switching" href="#Exhaustive-Switching">Exhaustive Switching</a></li>
<li><a id="toc-Switching-with-Enum-Literals" href="#Switching-with-Enum-Literals">Switching with Enum Literals</a></li>
</ul></li>
<li><a id="toc-while" href="#while">while</a>
<ul>
<li><a id="toc-Labeled-while" href="#Labeled-while">Labeled while</a></li>
<li><a id="toc-while-with-Optionals" href="#while-with-Optionals">while with Optionals</a></li>
<li><a id="toc-while-with-Error-Unions" href="#while-with-Error-Unions">while with Error Unions</a></li>
<li><a id="toc-inline-while" href="#inline-while">inline while</a></li>
</ul></li>
<li><a id="toc-for" href="#for">for</a>
<ul>
<li><a id="toc-Labeled-for" href="#Labeled-for">Labeled for</a></li>
<li><a id="toc-inline-for" href="#inline-for">inline for</a></li>
</ul></li>
<li><a id="toc-if" href="#if">if</a></li>
<li><a id="toc-defer" href="#defer">defer</a></li>
<li><a id="toc-unreachable" href="#unreachable">unreachable</a>
<ul>
<li><a id="toc-Basics" href="#Basics">Basics</a></li>
<li><a id="toc-At-Compile-Time" href="#At-Compile-Time">At Compile-Time</a></li>
</ul></li>
<li><a id="toc-noreturn" href="#noreturn">noreturn</a></li>
<li><a id="toc-Functions" href="#Functions">Functions</a>
<ul>
<li><a id="toc-Pass-by-value-Parameters" href="#Pass-by-value-Parameters">Pass-by-value Parameters</a></li>
<li><a id="toc-Function-Parameter-Type-Inference" href="#Function-Parameter-Type-Inference">Function Parameter Type Inference</a></li>
<li><a id="toc-Function-Reflection" href="#Function-Reflection">Function Reflection</a></li>
</ul></li>
<li><a id="toc-Errors" href="#Errors">Errors</a>
<ul>
<li><a id="toc-Error-Set-Type" href="#Error-Set-Type">Error Set Type</a>
<ul>
<li><a id="toc-The-Global-Error-Set" href="#The-Global-Error-Set">The Global Error Set</a></li>
</ul></li>
<li><a id="toc-Error-Union-Type" href="#Error-Union-Type">Error Union Type</a>
<ul>
<li><a id="toc-catch" href="#catch">catch</a></li>
<li><a id="toc-try" href="#try">try</a></li>
<li><a id="toc-errdefer" href="#errdefer">errdefer</a></li>
<li><a id="toc-Merging-Error-Sets" href="#Merging-Error-Sets">Merging Error Sets</a></li>
<li><a id="toc-Inferred-Error-Sets" href="#Inferred-Error-Sets">Inferred Error Sets</a></li>
</ul></li>
<li><a id="toc-Error-Return-Traces" href="#Error-Return-Traces">Error Return Traces</a>
<ul>
<li><a id="toc-Implementation-Details" href="#Implementation-Details">Implementation Details</a></li>
</ul></li>
</ul></li>
<li><a id="toc-Optionals" href="#Optionals">Optionals</a>
<ul>
<li><a id="toc-Optional-Type" href="#Optional-Type">Optional Type</a></li>
<li><a id="toc-null" href="#null">null</a></li>
<li><a id="toc-Optional-Pointers" href="#Optional-Pointers">Optional Pointers</a></li>
</ul></li>
<li><a id="toc-Casting" href="#Casting">Casting</a>
<ul>
<li><a id="toc-Type-Coercion" href="#Type-Coercion">Type Coercion</a>
<ul>
<li><a id="toc-Type-Coercion-Stricter-Qualification" href="#Type-Coercion-Stricter-Qualification">Type Coercion: Stricter Qualification</a></li>
<li><a id="toc-Type-Coercion-Integer-and-Float-Widening" href="#Type-Coercion-Integer-and-Float-Widening">Type Coercion: Integer and Float Widening</a></li>
<li><a id="toc-Type-Coercion-Coercion-Float-to-Int" href="#Type-Coercion-Coercion-Float-to-Int">Type Coercion: Coercion Float to Int</a></li>
<li><a id="toc-Type-Coercion-Slices-Arrays-and-Pointers" href="#Type-Coercion-Slices-Arrays-and-Pointers">Type Coercion: Slices, Arrays and Pointers</a></li>
<li><a id="toc-Type-Coercion-Optionals" href="#Type-Coercion-Optionals">Type Coercion: Optionals</a></li>
<li><a id="toc-Type-Coercion-Error-Unions" href="#Type-Coercion-Error-Unions">Type Coercion: Error Unions</a></li>
<li><a id="toc-Type-Coercion-Compile-Time-Known-Numbers" href="#Type-Coercion-Compile-Time-Known-Numbers">Type Coercion: Compile-Time Known Numbers</a></li>
<li><a id="toc-Type-Coercion-unions-and-enums" href="#Type-Coercion-unions-and-enums">Type Coercion: unions and enums</a></li>
<li><a id="toc-Type-Coercion-Zero-Bit-Types" href="#Type-Coercion-Zero-Bit-Types">Type Coercion: Zero Bit Types</a></li>
<li><a id="toc-Type-Coercion-undefined" href="#Type-Coercion-undefined">Type Coercion: undefined</a></li>
</ul></li>
<li><a id="toc-Explicit-Casts" href="#Explicit-Casts">Explicit Casts</a></li>
<li><a id="toc-Peer-Type-Resolution" href="#Peer-Type-Resolution">Peer Type Resolution</a></li>
</ul></li>
<li><a id="toc-Zero-Bit-Types" href="#Zero-Bit-Types">Zero Bit Types</a>
<ul>
<li><a id="toc-void" href="#void">void</a></li>
<li><a id="toc-Pointers-to-Zero-Bit-Types" href="#Pointers-to-Zero-Bit-Types">Pointers to Zero Bit Types</a></li>
</ul></li>
<li><a id="toc-Result-Location-Semantics" href="#Result-Location-Semantics">Result Location Semantics</a></li>
<li><a id="toc-usingnamespace" href="#usingnamespace">usingnamespace</a></li>
<li><a id="toc-comptime" href="#comptime">comptime</a>
<ul>
<li><a id="toc-Introducing-the-Compile-Time-Concept" href="#Introducing-the-Compile-Time-Concept">Introducing the Compile-Time Concept</a>
<ul>
<li><a id="toc-Compile-Time-Parameters" href="#Compile-Time-Parameters">Compile-Time Parameters</a></li>
<li><a id="toc-Compile-Time-Variables" href="#Compile-Time-Variables">Compile-Time Variables</a></li>
<li><a id="toc-Compile-Time-Expressions" href="#Compile-Time-Expressions">Compile-Time Expressions</a></li>
</ul></li>
<li><a id="toc-Generic-Data-Structures" href="#Generic-Data-Structures">Generic Data Structures</a></li>
<li><a id="toc-Case-Study-printf-in-Zig" href="#Case-Study-printf-in-Zig">Case Study: printf in Zig</a></li>
</ul></li>
<li><a id="toc-Assembly" href="#Assembly">Assembly</a>
<ul>
<li><a id="toc-Output-Constraints" href="#Output-Constraints">Output Constraints</a></li>
<li><a id="toc-Input-Constraints" href="#Input-Constraints">Input Constraints</a></li>
<li><a id="toc-Clobbers" href="#Clobbers">Clobbers</a></li>
<li><a id="toc-Global-Assembly" href="#Global-Assembly">Global Assembly</a></li>
</ul></li>
<li><a id="toc-Atomics" href="#Atomics">Atomics</a></li>
<li><a id="toc-Async-Functions" href="#Async-Functions">Async Functions</a>
<ul>
<li><a id="toc-Suspend-and-Resume" href="#Suspend-and-Resume">Suspend and Resume</a>
<ul>
<li><a id="toc-Resuming-from-Suspend-Blocks" href="#Resuming-from-Suspend-Blocks">Resuming from Suspend Blocks</a></li>
</ul></li>
<li><a id="toc-Async-and-Await" href="#Async-and-Await">Async and Await</a></li>
<li><a id="toc-Async-Function-Example" href="#Async-Function-Example">Async Function Example</a></li>
</ul></li>
<li><a id="toc-Builtin-Functions" href="#Builtin-Functions">Builtin Functions</a>
<ul style="columns: 2">
<li><a id="toc-addWithOverflow" href="#addWithOverflow">@addWithOverflow</a></li>
<li><a id="toc-addWithSaturation" href="#addWithSaturation">@addWithSaturation</a></li>
<li><a id="toc-alignCast" href="#alignCast">@alignCast</a></li>
<li><a id="toc-alignOf" href="#alignOf">@alignOf</a></li>
<li><a id="toc-as" href="#as">@as</a></li>
<li><a id="toc-asyncCall" href="#asyncCall">@asyncCall</a></li>
<li><a id="toc-atomicLoad" href="#atomicLoad">@atomicLoad</a></li>
<li><a id="toc-atomicRmw" href="#atomicRmw">@atomicRmw</a></li>
<li><a id="toc-atomicStore" href="#atomicStore">@atomicStore</a></li>
<li><a id="toc-bitCast" href="#bitCast">@bitCast</a></li>
<li><a id="toc-bitOffsetOf" href="#bitOffsetOf">@bitOffsetOf</a></li>
<li><a id="toc-boolToInt" href="#boolToInt">@boolToInt</a></li>
<li><a id="toc-bitSizeOf" href="#bitSizeOf">@bitSizeOf</a></li>
<li><a id="toc-breakpoint" href="#breakpoint">@breakpoint</a></li>
<li><a id="toc-mulAdd" href="#mulAdd">@mulAdd</a></li>
<li><a id="toc-byteSwap" href="#byteSwap">@byteSwap</a></li>
<li><a id="toc-bitReverse" href="#bitReverse">@bitReverse</a></li>
<li><a id="toc-offsetOf" href="#offsetOf">@offsetOf</a></li>
<li><a id="toc-call" href="#call">@call</a></li>
<li><a id="toc-cDefine" href="#cDefine">@cDefine</a></li>
<li><a id="toc-cImport" href="#cImport">@cImport</a></li>
<li><a id="toc-cInclude" href="#cInclude">@cInclude</a></li>
<li><a id="toc-clz" href="#clz">@clz</a></li>
<li><a id="toc-cmpxchgStrong" href="#cmpxchgStrong">@cmpxchgStrong</a></li>
<li><a id="toc-cmpxchgWeak" href="#cmpxchgWeak">@cmpxchgWeak</a></li>
<li><a id="toc-compileError" href="#compileError">@compileError</a></li>
<li><a id="toc-compileLog" href="#compileLog">@compileLog</a></li>
<li><a id="toc-ctz" href="#ctz">@ctz</a></li>
<li><a id="toc-cUndef" href="#cUndef">@cUndef</a></li>
<li><a id="toc-divExact" href="#divExact">@divExact</a></li>
<li><a id="toc-divFloor" href="#divFloor">@divFloor</a></li>
<li><a id="toc-divTrunc" href="#divTrunc">@divTrunc</a></li>
<li><a id="toc-embedFile" href="#embedFile">@embedFile</a></li>
<li><a id="toc-enumToInt" href="#enumToInt">@enumToInt</a></li>
<li><a id="toc-errorName" href="#errorName">@errorName</a></li>
<li><a id="toc-errorReturnTrace" href="#errorReturnTrace">@errorReturnTrace</a></li>
<li><a id="toc-errorToInt" href="#errorToInt">@errorToInt</a></li>
<li><a id="toc-errSetCast" href="#errSetCast">@errSetCast</a></li>
<li><a id="toc-export" href="#export">@export</a></li>
<li><a id="toc-extern" href="#extern">@extern</a></li>
<li><a id="toc-fence" href="#fence">@fence</a></li>
<li><a id="toc-field" href="#field">@field</a></li>
<li><a id="toc-fieldParentPtr" href="#fieldParentPtr">@fieldParentPtr</a></li>
<li><a id="toc-floatCast" href="#floatCast">@floatCast</a></li>
<li><a id="toc-floatToInt" href="#floatToInt">@floatToInt</a></li>
<li><a id="toc-frame" href="#frame">@frame</a></li>
<li><a id="toc-Frame" href="#Frame">@Frame</a></li>
<li><a id="toc-frameAddress" href="#frameAddress">@frameAddress</a></li>
<li><a id="toc-frameSize" href="#frameSize">@frameSize</a></li>
<li><a id="toc-hasDecl" href="#hasDecl">@hasDecl</a></li>
<li><a id="toc-hasField" href="#hasField">@hasField</a></li>
<li><a id="toc-import" href="#import">@import</a></li>
<li><a id="toc-intCast" href="#intCast">@intCast</a></li>
<li><a id="toc-intToEnum" href="#intToEnum">@intToEnum</a></li>
<li><a id="toc-intToError" href="#intToError">@intToError</a></li>
<li><a id="toc-intToFloat" href="#intToFloat">@intToFloat</a></li>
<li><a id="toc-intToPtr" href="#intToPtr">@intToPtr</a></li>
<li><a id="toc-maximum" href="#maximum">@maximum</a></li>
<li><a id="toc-memcpy" href="#memcpy">@memcpy</a></li>
<li><a id="toc-memset" href="#memset">@memset</a></li>
<li><a id="toc-minimum" href="#minimum">@minimum</a></li>
<li><a id="toc-wasmMemorySize" href="#wasmMemorySize">@wasmMemorySize</a></li>
<li><a id="toc-wasmMemoryGrow" href="#wasmMemoryGrow">@wasmMemoryGrow</a></li>
<li><a id="toc-mod" href="#mod">@mod</a></li>
<li><a id="toc-mulWithOverflow" href="#mulWithOverflow">@mulWithOverflow</a></li>
<li><a id="toc-mulWithSaturation" href="#mulWithSaturation">@mulWithSaturation</a></li>
<li><a id="toc-panic" href="#panic">@panic</a></li>
<li><a id="toc-popCount" href="#popCount">@popCount</a></li>
<li><a id="toc-ptrCast" href="#ptrCast">@ptrCast</a></li>
<li><a id="toc-ptrToInt" href="#ptrToInt">@ptrToInt</a></li>
<li><a id="toc-rem" href="#rem">@rem</a></li>
<li><a id="toc-returnAddress" href="#returnAddress">@returnAddress</a></li>
<li><a id="toc-select" href="#select">@select</a></li>
<li><a id="toc-setAlignStack" href="#setAlignStack">@setAlignStack</a></li>
<li><a id="toc-setCold" href="#setCold">@setCold</a></li>
<li><a id="toc-setEvalBranchQuota" href="#setEvalBranchQuota">@setEvalBranchQuota</a></li>
<li><a id="toc-setFloatMode" href="#setFloatMode">@setFloatMode</a></li>
<li><a id="toc-setRuntimeSafety" href="#setRuntimeSafety">@setRuntimeSafety</a></li>
<li><a id="toc-shlExact" href="#shlExact">@shlExact</a></li>
<li><a id="toc-shlWithOverflow" href="#shlWithOverflow">@shlWithOverflow</a></li>
<li><a id="toc-shlWithSaturation" href="#shlWithSaturation">@shlWithSaturation</a></li>
<li><a id="toc-shrExact" href="#shrExact">@shrExact</a></li>
<li><a id="toc-shuffle" href="#shuffle">@shuffle</a></li>
<li><a id="toc-sizeOf" href="#sizeOf">@sizeOf</a></li>
<li><a id="toc-splat" href="#splat">@splat</a></li>
<li><a id="toc-reduce" href="#reduce">@reduce</a></li>
<li><a id="toc-src" href="#src">@src</a></li>
<li><a id="toc-sqrt" href="#sqrt">@sqrt</a></li>
<li><a id="toc-sin" href="#sin">@sin</a></li>
<li><a id="toc-cos" href="#cos">@cos</a></li>
<li><a id="toc-exp" href="#exp">@exp</a></li>
<li><a id="toc-exp2" href="#exp2">@exp2</a></li>
<li><a id="toc-log" href="#log">@log</a></li>
<li><a id="toc-log2" href="#log2">@log2</a></li>
<li><a id="toc-log10" href="#log10">@log10</a></li>
<li><a id="toc-fabs" href="#fabs">@fabs</a></li>
<li><a id="toc-floor" href="#floor">@floor</a></li>
<li><a id="toc-ceil" href="#ceil">@ceil</a></li>
<li><a id="toc-trunc" href="#trunc">@trunc</a></li>
<li><a id="toc-round" href="#round">@round</a></li>
<li><a id="toc-subWithOverflow" href="#subWithOverflow">@subWithOverflow</a></li>
<li><a id="toc-subWithSaturation" href="#subWithSaturation">@subWithSaturation</a></li>
<li><a id="toc-tagName" href="#tagName">@tagName</a></li>
<li><a id="toc-This" href="#This">@This</a></li>
<li><a id="toc-truncate" href="#truncate">@truncate</a></li>
<li><a id="toc-Type" href="#Type">@Type</a></li>
<li><a id="toc-typeInfo" href="#typeInfo">@typeInfo</a></li>
<li><a id="toc-typeName" href="#typeName">@typeName</a></li>
<li><a id="toc-TypeOf" href="#TypeOf">@TypeOf</a></li>
<li><a id="toc-unionInit" href="#unionInit">@unionInit</a></li>
</ul></li>
<li><a id="toc-Build-Mode" href="#Build-Mode">Build Mode</a>
<ul>
<li><a id="toc-Debug" href="#Debug">Debug</a></li>
<li><a id="toc-ReleaseFast" href="#ReleaseFast">ReleaseFast</a></li>
<li><a id="toc-ReleaseSafe" href="#ReleaseSafe">ReleaseSafe</a></li>
<li><a id="toc-ReleaseSmall" href="#ReleaseSmall">ReleaseSmall</a></li>
</ul></li>
<li><a id="toc-Single-Threaded-Builds" href="#Single-Threaded-Builds">Single Threaded Builds</a></li>
<li><a id="toc-Undefined-Behavior" href="#Undefined-Behavior">Undefined Behavior</a>
<ul>
<li><a id="toc-Reaching-Unreachable-Code" href="#Reaching-Unreachable-Code">Reaching Unreachable Code</a></li>
<li><a id="toc-Index-out-of-Bounds" href="#Index-out-of-Bounds">Index out of Bounds</a></li>
<li><a id="toc-Cast-Negative-Number-to-Unsigned-Integer" href="#Cast-Negative-Number-to-Unsigned-Integer">Cast Negative Number to Unsigned Integer</a></li>
<li><a id="toc-Cast-Truncates-Data" href="#Cast-Truncates-Data">Cast Truncates Data</a></li>
<li><a id="toc-Integer-Overflow" href="#Integer-Overflow">Integer Overflow</a>
<ul>
<li><a id="toc-Default-Operations" href="#Default-Operations">Default Operations</a></li>
<li><a id="toc-Standard-Library-Math-Functions" href="#Standard-Library-Math-Functions">Standard Library Math Functions</a></li>
<li><a id="toc-Builtin-Overflow-Functions" href="#Builtin-Overflow-Functions">Builtin Overflow Functions</a></li>
<li><a id="toc-Wrapping-Operations" href="#Wrapping-Operations">Wrapping Operations</a></li>
</ul></li>
<li><a id="toc-Exact-Left-Shift-Overflow" href="#Exact-Left-Shift-Overflow">Exact Left Shift Overflow</a></li>
<li><a id="toc-Exact-Right-Shift-Overflow" href="#Exact-Right-Shift-Overflow">Exact Right Shift Overflow</a></li>
<li><a id="toc-Division-by-Zero" href="#Division-by-Zero">Division by Zero</a></li>
<li><a id="toc-Remainder-Division-by-Zero" href="#Remainder-Division-by-Zero">Remainder Division by Zero</a></li>
<li><a id="toc-Exact-Division-Remainder" href="#Exact-Division-Remainder">Exact Division Remainder</a></li>
<li><a id="toc-Attempt-to-Unwrap-Null" href="#Attempt-to-Unwrap-Null">Attempt to Unwrap Null</a></li>
<li><a id="toc-Attempt-to-Unwrap-Error" href="#Attempt-to-Unwrap-Error">Attempt to Unwrap Error</a></li>
<li><a id="toc-Invalid-Error-Code" href="#Invalid-Error-Code">Invalid Error Code</a></li>
<li><a id="toc-Invalid-Enum-Cast" href="#Invalid-Enum-Cast">Invalid Enum Cast</a></li>
<li><a id="toc-Invalid-Error-Set-Cast" href="#Invalid-Error-Set-Cast">Invalid Error Set Cast</a></li>
<li><a id="toc-Incorrect-Pointer-Alignment" href="#Incorrect-Pointer-Alignment">Incorrect Pointer Alignment</a></li>
<li><a id="toc-Wrong-Union-Field-Access" href="#Wrong-Union-Field-Access">Wrong Union Field Access</a></li>
<li><a id="toc-Out-of-Bounds-Float-to-Integer-Cast" href="#Out-of-Bounds-Float-to-Integer-Cast">Out of Bounds Float to Integer Cast</a></li>
<li><a id="toc-Pointer-Cast-Invalid-Null" href="#Pointer-Cast-Invalid-Null">Pointer Cast Invalid Null</a></li>
</ul></li>
<li><a id="toc-Memory" href="#Memory">Memory</a>
<ul>
<li><a id="toc-Choosing-an-Allocator" href="#Choosing-an-Allocator">Choosing an Allocator</a></li>
<li><a id="toc-Where-are-the-bytes" href="#Where-are-the-bytes">Where are the bytes?</a></li>
<li><a id="toc-Implementing-an-Allocator" href="#Implementing-an-Allocator">Implementing an Allocator</a></li>
<li><a id="toc-Heap-Allocation-Failure" href="#Heap-Allocation-Failure">Heap Allocation Failure</a></li>
<li><a id="toc-Recursion" href="#Recursion">Recursion</a></li>
<li><a id="toc-Lifetime-and-Ownership" href="#Lifetime-and-Ownership">Lifetime and Ownership</a></li>
</ul></li>
<li><a id="toc-Compile-Variables" href="#Compile-Variables">Compile Variables</a></li>
<li><a id="toc-Root-Source-File" href="#Root-Source-File">Root Source File</a></li>
<li><a id="toc-Zig-Build-System" href="#Zig-Build-System">Zig Build System</a>
<ul>
<li><a id="toc-Building-an-Executable" href="#Building-an-Executable">Building an Executable</a></li>
<li><a id="toc-Building-a-Library" href="#Building-a-Library">Building a Library</a></li>
<li><a id="toc-Compiling-C-Source-Code" href="#Compiling-C-Source-Code">Compiling C Source Code</a></li>
</ul></li>
<li><a id="toc-C" href="#C">C</a>
<ul>
<li><a id="toc-C-Type-Primitives" href="#C-Type-Primitives">C Type Primitives</a></li>
<li><a id="toc-Import-from-C-Header-File" href="#Import-from-C-Header-File">Import from C Header File</a></li>
<li><a id="toc-C-Translation-CLI" href="#C-Translation-CLI">C Translation CLI</a>
<ul>
<li><a id="toc-Command-line-flags" href="#Command-line-flags">Command line flags</a></li>
<li><a id="toc-Using--target-and--cflags" href="#Using--target-and--cflags">Using -target and -cflags</a></li>
<li><a id="toc-cImport-vs-translate-c" href="#cImport-vs-translate-c">@cImport vs translate-c</a></li>
</ul></li>
<li><a id="toc-C-Translation-Caching" href="#C-Translation-Caching">C Translation Caching</a></li>
<li><a id="toc-Translation-failures" href="#Translation-failures">Translation failures</a></li>
<li><a id="toc-C-Macros" href="#C-Macros">C Macros</a></li>
<li><a id="toc-C-Pointers" href="#C-Pointers">C Pointers</a></li>
<li><a id="toc-Exporting-a-C-Library" href="#Exporting-a-C-Library">Exporting a C Library</a></li>
<li><a id="toc-Mixing-Object-Files" href="#Mixing-Object-Files">Mixing Object Files</a></li>
</ul></li>
<li><a id="toc-WebAssembly" href="#WebAssembly">WebAssembly</a>
<ul>
<li><a id="toc-Freestanding" href="#Freestanding">Freestanding</a></li>
<li><a id="toc-WASI" href="#WASI">WASI</a></li>
</ul></li>
<li><a id="toc-Targets" href="#Targets">Targets</a></li>
<li><a id="toc-Style-Guide" href="#Style-Guide">Style Guide</a>
<ul>
<li><a id="toc-Whitespace" href="#Whitespace">Whitespace</a></li>
<li><a id="toc-Names" href="#Names">Names</a></li>
<li><a id="toc-Examples" href="#Examples">Examples</a></li>
<li><a id="toc-Doc-Comment-Guidance" href="#Doc-Comment-Guidance">Doc Comment Guidance</a></li>
</ul></li>
<li><a id="toc-Source-Encoding" href="#Source-Encoding">Source Encoding</a></li>
<li><a id="toc-Keyword-Reference" href="#Keyword-Reference">Keyword Reference</a></li>
<li><a id="toc-Grammar" href="#Grammar">Grammar</a></li>
<li><a id="toc-Zen" href="#Zen">Zen</a></li>
</ul>
</nav>
</div>
<div id="contents-wrapper"><main id="contents">
<h2 id="Introduction"><a href="#toc-Introduction">Introduction</a> <a class="hdr" href="#Introduction">§</a></h2>
<p>
<a href="https://ziglang.org">Zig</a> is a general-purpose programming language and toolchain for maintaining
<strong>robust</strong>, <strong>optimal</strong>, and <strong>reusable</strong> software.
</p>
<dl>
<dt>Robust</dt><dd>Behavior is correct even for edge cases such as out of memory.</dd>
<dt>Optimal</dt><dd>Write programs the best way they can behave and perform.</dd>
<dt>Reusable</dt><dd>The same code works in many environments which have different
constraints.</dd>
<dt>Maintainable</dt><dd>Precisely communicate intent to the compiler and
other programmers. The language imposes a low overhead to reading code and is
resilient to changing requirements and environments.</dd>
</dl>
<p>
Often the most efficient way to learn something new is to see examples, so
this documentation shows how to use each of Zig's features. It is
all on one page so you can search with your browser's search tool.
</p>
<p>
The code samples in this document are compiled and tested as part of the main test suite of Zig.
</p>
<p>
This HTML document depends on no external files, so you can use it offline.
</p>
<h2 id="Zig-Standard-Library"><a href="#toc-Zig-Standard-Library">Zig Standard Library</a> <a class="hdr" href="#Zig-Standard-Library">§</a></h2>
<p>
The <a href="https://ziglang.org/documentation/master/std/">Zig Standard Library</a> has its own documentation.
</p>
<p>
Zig's Standard Library contains commonly used algorithms, data structures, and definitions to help you build programs or libraries.
You will see many examples of Zig's Standard Library used in this documentation. To learn more about the Zig Standard Library,
visit the link above.
</p>
<h2 id="Hello-World"><a href="#toc-Hello-World">Hello World</a> <a class="hdr" href="#Hello-World">§</a></h2>
<figure><figcaption class="zig-cap"><cite class="file">hello.zig</cite></figcaption><pre><code><span class="tok-kw">const</span> std = <span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>);
<span class="tok-kw">pub</span> <span class="tok-kw">fn</span> <span class="tok-fn">main</span>() !<span class="tok-type">void</span> {
<span class="tok-kw">const</span> stdout = std.io.getStdOut().writer();
<span class="tok-kw">try</span> stdout.print(<span class="tok-str">"Hello, {s}!\n"</span>, .{<span class="tok-str">"world"</span>});
}</code></pre></figure><figure><figcaption class="shell-cap">Shell</figcaption><pre><samp>$ <kbd>zig build-exe hello.zig</kbd>
$ <kbd>./hello</kbd>
Hello, world!
</samp></pre></figure>
<p>
The Zig code sample above demonstrates one way to create a program that will output: <samp>Hello, world!</samp>.
</p>
<p>
The code sample shows the contents of a file named <code class="file">hello.zig</code>. Files storing Zig
source code are <a href="#Source-Encoding">UTF-8 encoded</a> text files. The files storing
Zig source code are usually named with the <code class="file"><em>.zig</em></code> extension.
</p>
<p>
Following the <code class="file">hello.zig</code> Zig code sample, the <a href="#Zig-Build-System">Zig Build System</a> is used
to build an executable program from the <code class="file">hello.zig</code> source code. Then, the
<code class="file">hello</code> program is executed showing its output <samp>Hello, world!</samp>. The
lines beginning with <samp>$</samp> represent command line prompts and a command.
Everything else is program output.
</p>
<p>
The code sample begins by adding the <a href="#Zig-Standard-Library">Zig Standard Library</a> to the build using the <a href="#import">@import</a> builtin function.
The <code><span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>)</code> function call creates a structure that represents the Zig Standard Library.
The code then <a href="#Container-Level-Variables">declares</a> a
<a href="#Assignment">constant identifier</a>, named <code>std</code>, that gives access the features of the Zig Standard Library.
</p>
<p>
Next, a <a href="#Functions">public function</a>, <code><span class="tok-kw">pub</span> <span class="tok-kw">fn</span></code>, named <code>main</code>
is declared. The <code>main</code> function is necessary because it tells the Zig compiler where the start of
the program exists. Programs designed to be executed will need a <code><span class="tok-kw">pub</span> <span class="tok-kw">fn</span> <span class="tok-fn">main</span></code> function.
</p>
<aside role="note" aria-label="Note about main function">
<p>
For more advanced use cases, Zig offers other features to inform the compiler where the start of
the program exists. Also, libraries do not need a <code><span class="tok-kw">pub</span> <span class="tok-kw">fn</span> <span class="tok-fn">main</span></code> function because
library code is called by other programs or libraries.
</p>
</aside>
<p>
A function is a block of any number of statements and expressions that, as a whole, perform a task.
Functions may or may not return data after they are done performing their task. If a function
cannot perform its task, it might return an error. Zig makes all of this explicit.
</p>
<p>
In the <code class="file">hello.zig</code> code sample, the <code>main</code> function is declared
with the <code>!<span class="tok-type">void</span></code> return type. This return type is known as an <a href="#Error-Union-Type">Error Union Type</a>.
This syntax tells the Zig compiler that the function will either return an
error or a value. An error union type combines an <a href="#Error-Set-Type">Error Set Type</a> and any other data type
(e.g. a <a href="#Primitive-Types">Primitive Type</a> or a user-defined type such as a <a href="#struct">struct</a>, <a href="#enum">enum</a>, or <a href="#union">union</a>).
The full form of an error union type is
<code><error set type></code><code>!</code><code><any data type></code>. In the code
sample, the error set type is not explicitly written on the left side of the <code>!</code> operator.
When written this way, the error set type is an <a href="#Inferred-Error-Sets">inferred error set type</a>. The
<code><span class="tok-type">void</span></code> after the <code>!</code> operator
tells the compiler that the function will not return a value under normal circumstances (i.e. when no errors occur).
</p>
<aside role="note" aria-label="Note to disambiguate exclamation mark operator">
<p>
Note to experienced programmers: Zig also has the boolean <a href="#Operators">operator</a> <code>!a</code>
where <code>a</code> is a value of type <code><span class="tok-type">bool</span></code>. Error union types contain the
name of the type in the syntax: <code>!</code><code><any data type></code>.
</p>
</aside>
<p>
In Zig, a function's block of statements and expressions are surrounded by an open curly-brace <code>{</code> and
close curly-brace <code>}</code>. Inside of the <code>main</code> function are expressions that perform
the task of outputting <samp>Hello, world!</samp> to standard output.
</p>
<p>
First, a constant identifier, <code>stdout</code>, is initialized to represent standard output's
writer. Then, the program tries to print the <samp>Hello, world!</samp>
message to standard output.
</p>
<p>
Functions sometimes need information to perform their task. In Zig, information is passed
to functions between an open parenthesis <code>(</code> and a close parenthesis <code>)</code> placed after
the function's name. This information is also known as arguments. When there are
multiple arguments passed to a function, they are separated by commas <code>,</code>.
</p>
<p>
The two arguments passed to the <code>stdout.print()</code> function, <code><span class="tok-str">"Hello, {s}!\n"</span></code>
and <code>.{<span class="tok-str">"world"</span>}</code>, are evaluated at <a href="#comptime">compile-time</a>. The code sample is
purposely written to show how to perform <a href="#String-Literals-and-Unicode-Code-Point-Literals">string</a>
substitution in the <code>print</code> function. The curly-braces inside of the first argument
are substituted with the compile-time known value inside of the second argument
(known as an <a href="#Anonymous-Struct-Literals">anonymous struct literal</a>). The <code>\n</code>
inside of the double-quotes of the first argument is the <a href="#Escape-Sequences">escape sequence</a> for the
newline character. The <a href="#try">try</a> expression evaluates the result of <code>stdout.print</code>.
If the result is an error, then the <code><span class="tok-kw">try</span></code> expression will return from
<code>main</code> with the error. Otherwise, the program will continue. In this case, there are no
more statements or expressions left to execute in the <code>main</code> function, so the program exits.
</p>
<p>
In Zig, the standard output writer's <code>print</code> function is allowed to fail because
it is actually a function defined as part of a generic Writer. Consider a generic Writer that
represents writing data to a file. When the disk is full, a write to the file will fail.
However, we typically do not expect writing text to the standard output to fail. To avoid having
to handle the failure case of printing to standard output, you can use alternate functions: the
functions in <code>std.log</code> for proper logging or the <code>std.debug.print</code> function.
This documentation will use the latter option to print to standard error (stderr) and silently return
on failure. The next code sample, <code class="file">hello_again.zig</code> demonstrates the use of
<code>std.debug.print</code>.
</p>
<figure><figcaption class="zig-cap"><cite class="file">hello_again.zig</cite></figcaption><pre><code><span class="tok-kw">const</span> print = <span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>).debug.print;
<span class="tok-kw">pub</span> <span class="tok-kw">fn</span> <span class="tok-fn">main</span>() <span class="tok-type">void</span> {
print(<span class="tok-str">"Hello, world!\n"</span>, .{});
}</code></pre></figure><figure><figcaption class="shell-cap">Shell</figcaption><pre><samp>$ <kbd>zig build-exe hello_again.zig</kbd>
$ <kbd>./hello_again</kbd>
Hello, world!
</samp></pre></figure>
<p>
Note that you can leave off the <code>!</code> from the return type because <code>std.debug.print</code> cannot fail.
</p>
<p>See also:</p><ul>
<li><a href="#Values">Values</a></li>
<li><a href="#import">@import</a></li>
<li><a href="#Errors">Errors</a></li>
<li><a href="#Root-Source-File">Root Source File</a></li>
<li><a href="#Source-Encoding">Source Encoding</a></li>
</ul>
<h2 id="Zig-Test"><a href="#toc-Zig-Test">Zig Test</a> <a class="hdr" href="#Zig-Test">§</a></h2>
<p>
<kbd>zig test</kbd> is a tool that can be used to quickly build and run Zig code
to make sure behavior meets expectations. <code><span class="tok-builtin">@import</span>(<span class="tok-str">"builtin"</span>).is_test</code>
is available for code to detect whether the current build is a test build.
</p>
<figure><figcaption class="zig-cap"><cite class="file">detect_test.zig</cite></figcaption><pre><code><span class="tok-kw">const</span> std = <span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>);
<span class="tok-kw">const</span> builtin = <span class="tok-builtin">@import</span>(<span class="tok-str">"builtin"</span>);
<span class="tok-kw">const</span> expect = std.testing.expect;
<span class="tok-kw">test</span> <span class="tok-str">"builtin.is_test"</span> {
<span class="tok-kw">try</span> expect(builtin.is_test);
}</code></pre></figure><figure><figcaption class="shell-cap">Shell</figcaption><pre><samp>$ <kbd>zig test detect_test.zig</kbd>
Test [1/1] test "builtin.is_test"...
All 1 tests passed.
</samp></pre></figure>
<p>
Zig has lazy top level declaration analysis, which means that if a function is not called,
or otherwise used, it is not analyzed. This means that there may be an undiscovered
compile error in a function because it is never called.
</p>
<figure><figcaption class="zig-cap"><cite class="file">unused_fn.zig</cite></figcaption><pre><code><span class="tok-kw">fn</span> <span class="tok-fn">unused</span>() <span class="tok-type">i32</span> {
<span class="tok-kw">return</span> <span class="tok-str">"wrong return type"</span>;
}
<span class="tok-kw">test</span> <span class="tok-str">"unused function"</span> { }</code></pre></figure><figure><figcaption class="shell-cap">Shell</figcaption><pre><samp>$ <kbd>zig test unused_fn.zig</kbd>
Test [1/1] test "unused function"...
All 1 tests passed.
</samp></pre></figure>
<p>
Note that, while in <a href="#Debug">Debug</a> and <a href="#ReleaseSafe">ReleaseSafe</a> modes, <a href="#unreachable">unreachable</a> emits a
call to <a href="#panic">@panic</a>, in <a href="#ReleaseFast">ReleaseFast</a> and <a href="#ReleaseSmall">ReleaseSmall</a> modes, it is really
undefined behavior. The implementation of <code>std.debug.assert</code> is as
simple as:
</p>
<figure><figcaption class="zig-cap"><cite class="file">assert.zig</cite></figcaption><pre><code><span class="tok-kw">pub</span> <span class="tok-kw">fn</span> <span class="tok-fn">assert</span>(ok: <span class="tok-type">bool</span>) <span class="tok-type">void</span> {
<span class="tok-kw">if</span> (!ok) <span class="tok-kw">unreachable</span>;
}</code></pre></figure>
<p>
This means that when testing in ReleaseFast or ReleaseSmall mode, <code>assert</code>
is not sufficient to check the result of a computation:
</p>
<figure><figcaption class="zig-cap"><cite class="file">assert_release_fast_mode.zig</cite></figcaption><pre><code><span class="tok-kw">const</span> std = <span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>);
<span class="tok-kw">const</span> assert = std.debug.assert;
<span class="tok-kw">test</span> <span class="tok-str">"assert in release fast mode"</span> {
assert(<span class="tok-null">false</span>);
}</code></pre></figure>
<p>
When compiling this test in <a href="#ReleaseFast">ReleaseFast</a> mode, it invokes unchecked
<a href="#Undefined-Behavior">Undefined Behavior</a>. Since that could do anything, this documentation
cannot show you the output.
</p>
<p>
Better practice for checking the output when testing is to use <code>std.testing.expect</code>:
</p>
<figure><figcaption class="zig-cap"><cite class="file">test.zig</cite></figcaption><pre><code><span class="tok-kw">const</span> std = <span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>);
<span class="tok-kw">const</span> expect = std.testing.expect;
<span class="tok-kw">test</span> <span class="tok-str">"expect in release fast mode"</span> {
<span class="tok-kw">try</span> expect(<span class="tok-null">false</span>);
}</code></pre></figure><figure><figcaption class="shell-cap">Shell</figcaption><pre><samp>$ <kbd>zig test test.zig -O ReleaseFast</kbd>
Test [1/1] test "expect in release fast mode"...
Test [2/1] test "expect in release fast mode"... FAIL (TestUnexpectedResult)
0 passed; 0 skipped; 1 failed.
error: the following test command failed with exit code 1:
docgen_tmp/zig-cache/o/4c538eebc0f9b6ad929266b9037088b9/test /home/paul/Development/Zig/zig-master/zig
</samp></pre></figure>
<p>See the rest of the <code>std.testing</code> namespace for more available functions.</p>
<p>
<kbd>zig test</kbd> has a few command line parameters which affect the compilation. See
<kbd>zig --help</kbd> for a full list. The most interesting one is <kbd>--test-filter [text]</kbd>.
This makes the test build only include tests whose name contains the supplied filter text.
Again, thanks to lazy analysis, this can allow you to narrow a build to only a few functions in
isolation.
</p>
<h2 id="Comments"><a href="#toc-Comments">Comments</a> <a class="hdr" href="#Comments">§</a></h2>
<figure><figcaption class="zig-cap"><cite class="file">comments.zig</cite></figcaption><pre><code><span class="tok-kw">const</span> expect = <span class="tok-builtin">@import</span>(<span class="tok-str">"std"</span>).testing.expect;
<span class="tok-kw">test</span> <span class="tok-str">"comments"</span> {
<span class="tok-comment">// Comments in Zig start with "//" and end at the next LF byte (end of line).</span>
<span class="tok-comment">// The below line is a comment, and won't be executed.</span>
<span class="tok-comment">//expect(false);</span>
<span class="tok-kw">const</span> x = <span class="tok-null">true</span>; <span class="tok-comment">// another comment</span>
<span class="tok-kw">try</span> expect(x);
}</code></pre></figure><figure><figcaption class="shell-cap">Shell</figcaption><pre><samp>$ <kbd>zig test comments.zig</kbd>
Test [1/1] test "comments"...
All 1 tests passed.
</samp></pre></figure>
<p>
There are no multiline comments in Zig (e.g. like <code class="c">/* */</code>
comments in C). This helps allow Zig to have the property that each line
of code can be tokenized out of context.
</p>
<h3 id="Doc-comments"><a href="#toc-Doc-comments">Doc comments</a> <a class="hdr" href="#Doc-comments">§</a></h3>
<p>
A doc comment is one that begins with exactly three slashes (i.e.
<code><span class="tok-comment">///</span></code> but not <code><span class="tok-comment">////</span></code>);
multiple doc comments in a row are merged together to form a multiline
doc comment. The doc comment documents whatever immediately follows it.
</p>
<figure><figcaption class="zig-cap"><cite class="file">doc_comments.zig</cite></figcaption><pre><code><span class="tok-comment">/// A structure for storing a timestamp, with nanosecond precision (this is a</span>
<span class="tok-comment">/// multiline doc comment).</span>
<span class="tok-kw">const</span> Timestamp = <span class="tok-kw">struct</span> {
<span class="tok-comment">/// The number of seconds since the epoch (this is also a doc comment).</span>
seconds: <span class="tok-type">i64</span>, <span class="tok-comment">// signed so we can represent pre-1970 (not a doc comment)</span>
<span class="tok-comment">/// The number of nanoseconds past the second (doc comment again).</span>
nanos: <span class="tok-type">u32</span>,
<span class="tok-comment">/// Returns a `Timestamp` struct representing the Unix epoch; that is, the</span>
<span class="tok-comment">/// moment of 1970 Jan 1 00:00:00 UTC (this is a doc comment too).</span>
<span class="tok-kw">pub</span> <span class="tok-kw">fn</span> <span class="tok-fn">unixEpoch</span>() Timestamp {
<span class="tok-kw">return</span> Timestamp{
.seconds = <span class="tok-number">0</span>,
.nanos = <span class="tok-number">0</span>,
};
}
};</code></pre></figure>