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langref.html.in
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langref.html.in
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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no" />
<title>Documentation - The Zig Programming Language</title>
<link rel="stylesheet" type="text/css" href="highlight/styles/default.css">
<style type="text/css">
table, th, td {
border-collapse: collapse;
border: 1px solid grey;
}
th, td {
padding: 0.1em;
}
@media screen and (min-width: 28.75em) {
#nav {
width: 20em;
height: 100%;
overflow-y: scroll;
position: fixed;
left: 0;
top: 0;
}
#contents {
max-width: 50em;
padding-left: 22em;
}
}
</style>
</head>
<body>
<div id="nav">
<ul>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#hello-world">Hello World</a></li>
<li><a href="#values">Values</a></li>
<ul>
<li><a href="#primitive-types">Primitive Types</a></li>
<li><a href="#primitive-values">Primitive Values</a></li>
<li><a href="#string-literals">String Literals</a>
<ul>
<li><a href="#string-literal-escapes">Escape Sequences</a></li>
<li><a href="#multiline-string-literals">Multiline String Literals</a></li>
</ul>
</li>
<li><a href="#values-assignment">Assignment</a></li>
</ul>
</li>
<li><a href="#integers">Integers</a>
<ul>
<li><a href="#integer-literals">Integer Literals</a></li>
<li><a href="#runtime-integer-values">Runtime Integer Values</a></li>
</ul>
</li>
<li><a href="#floats">Floats</a>
<ul>
<li><a href="#float-literals">Float Literals</a></li>
<li><a href="#float-operations">Floating Point Operations</a></li>
</ul>
</li>
<li><a href="#operators">Operators</a>
<ul>
<li><a href="#operators-table">Table of Operators</a></li>
<li><a href="#operators-precedence">Precedence</a></li>
</ul>
</li>
<li><a href="#arrays">Arrays</a></li>
<li><a href="#pointers">Pointers</a>
<ul>
<li><a href="#alignment">Alignment</a></li>
<li><a href="#type-based-alias-analysis">Type Based Alias Analysis</a></li>
</ul>
</li>
<li><a href="#slices">Slices</a></li>
<li><a href="#struct">struct</a></li>
<li><a href="#enum">enum</a></li>
<li><a href="#union">union</a></li>
<li><a href="#switch">switch</a></li>
<li><a href="#while">while</a></li>
<li><a href="#for">for</a></li>
<li><a href="#if">if</a></li>
<li><a href="#goto">goto</a></li>
<li><a href="#defer">defer</a></li>
<li><a href="#unreachable">unreachable</a>
<ul>
<li><a href="#unreachable-basics">Basics</a></li>
<li><a href="#unreachable-comptime">At Compile-Time</a></li>
</ul>
</li>
<li><a href="#noreturn">noreturn</a></li>
<li><a href="#functions">Functions</a>
<ul>
<li><a href="#functions-by-val-params">Pass-by-val Parameters</a>
</ul>
</li>
<li><a href="#errors">Errors</a></li>
<li><a href="#nullables">Nullables</a></li>
<li><a href="#casting">Casting</a></li>
<li><a href="#void">void</a></li>
<li><a href="#this">this</a></li>
<li><a href="#comptime">comptime</a>
<ul>
<li><a href="#introducing-compile-time-concept">Introducing the Compile-Time Concept</a></li>
<ul>
<li><a href="#compile-time-parameters">Compile-time parameters</a></li>
<li><a href="#compile-time-variables">Compile-time variables</a></li>
<li><a href="#compile-time-expressions">Compile-time expressions</a></li>
</ul>
<li><a href="#generic-data-structures">Generic Data Structures</a></li>
<li><a href="#case-study-printf">Case Study: printf in Zig</a></li>
</ul>
</li>
<li><a href="#inline">inline</a></li>
<li><a href="#assembly">assembly</a></li>
<li><a href="#atomics">Atomics</a></li>
<li><a href="#builtin-functions">Builtin Functions</a>
<ul>
<li><a href="#builtin-addWithOverflow">@addWithOverflow</a></li>
<li><a href="#builtin-alignCast">@alignCast</a></li>
<li><a href="#builtin-alignOf">@alignOf</a></li>
<li><a href="#builtin-ArgType">@ArgType</a></li>
<li><a href="#builtin-bitCast">@bitCast</a></li>
<li><a href="#builtin-breakpoint">@breakpoint</a></li>
<li><a href="#builtin-cDefine">@cDefine</a></li>
<li><a href="#builtin-cImport">@cImport</a></li>
<li><a href="#builtin-cInclude">@cInclude</a></li>
<li><a href="#builtin-cUndef">@cUndef</a></li>
<li><a href="#builtin-canImplicitCast">@canImplicitCast</a></li>
<li><a href="#builtin-clz">@clz</a></li>
<li><a href="#builtin-cmpxchg">@cmpxchg</a></li>
<li><a href="#builtin-compileError">@compileError</a></li>
<li><a href="#builtin-compileLog">@compileLog</a></li>
<li><a href="#builtin-ctz">@ctz</a></li>
<li><a href="#builtin-divExact">@divExact</a></li>
<li><a href="#builtin-divFloor">@divFloor</a></li>
<li><a href="#builtin-divTrunc">@divTrunc</a></li>
<li><a href="#builtin-embedFile">@embedFile</a></li>
<li><a href="#builtin-enumTagName">@enumTagName</a></li>
<li><a href="#builtin-EnumTagType">@EnumTagType</a></li>
<li><a href="#builtin-errorName">@errorName</a></li>
<li><a href="#builtin-fence">@fence</a></li>
<li><a href="#builtin-fieldParentPtr">@fieldParentPtr</a></li>
<li><a href="#builtin-frameAddress">@frameAddress</a></li>
<li><a href="#builtin-import">@import</a></li>
<li><a href="#builtin-inlineCall">@inlineCall</a></li>
<li><a href="#builtin-intToPtr">@intToPtr</a></li>
<li><a href="#builtin-IntType">@IntType</a></li>
<li><a href="#builtin-maxValue">@maxValue</a></li>
<li><a href="#builtin-memberCount">@memberCount</a></li>
<li><a href="#builtin-memberName">@memberName</a></li>
<li><a href="#builtin-memberType">@memberType</a></li>
<li><a href="#builtin-memcpy">@memcpy</a></li>
<li><a href="#builtin-memset">@memset</a></li>
<li><a href="#builtin-minValue">@minValue</a></li>
<li><a href="#builtin-mod">@mod</a></li>
<li><a href="#builtin-mulWithOverflow">@mulWithOverflow</a></li>
<li><a href="#builtin-offsetOf">@offsetOf</a></li>
<li><a href="#builtin-OpaqueType">@OpaqueType</a></li>
<li><a href="#builtin-panic">@panic</a></li>
<li><a href="#builtin-ptrCast">@ptrCast</a></li>
<li><a href="#builtin-ptrToInt">@ptrToInt</a></li>
<li><a href="#builtin-rem">@rem</a></li>
<li><a href="#builtin-returnAddress">@returnAddress</a></li>
<li><a href="#builtin-setDebugSafety">@setDebugSafety</a></li>
<li><a href="#builtin-setEvalBranchQuota">@setEvalBranchQuota</a></li>
<li><a href="#builtin-setFloatMode">@setFloatMode</a></li>
<li><a href="#builtin-setGlobalLinkage">@setGlobalLinkage</a></li>
<li><a href="#builtin-setGlobalSection">@setGlobalSection</a></li>
<li><a href="#builtin-shlExact">@shlExact</a></li>
<li><a href="#builtin-shlWithOverflow">@shlWithOverflow</a></li>
<li><a href="#builtin-shrExact">@shrExact</a></li>
<li><a href="#builtin-sizeOf">@sizeOf</a></li>
<li><a href="#builtin-subWithOverflow">@subWithOverflow</a></li>
<li><a href="#builtin-truncate">@truncate</a></li>
<li><a href="#builtin-typeId">@typeId</a></li>
<li><a href="#builtin-typeName">@typeName</a></li>
<li><a href="#builtin-typeOf">@typeOf</a></li>
</ul>
</li>
<li><a href="#build-mode">Build Mode</a>
<ul>
<li><a href="#build-mode-debug">Debug</a></li>
<li><a href="#build-mode-release-fast">ReleaseFast</a></li>
<li><a href="#build-mode-release-safe">ReleaseSafe</a></li>
</ul>
</li>
<li><a href="#undefined-behavior">Undefined Behavior</a>
<ul>
<li><a href="#undef-unreachable">Reaching Unreachable Code</a></li>
<li><a href="#undef-index-out-of-bounds">Index out of Bounds</a></li>
<li><a href="#undef-cast-negative-unsigned">Cast Negative Number to Unsigned Integer</a></li>
<li><a href="#undef-cast-truncates-data">Cast Truncates Data</a></li>
<li><a href="#undef-integer-overflow">Integer Overflow</a>
<ul>
<li><a href="#undef-int-overflow-default">Default Operations</a></li>
<li><a href="#undef-int-overflow-std">Standard Library Math Functions</a></li>
<li><a href="#undef-int-overflow-builtin">Builtin Overflow Functions</a></li>
<li><a href="#undef-int-overflow-wrap">Wrapping Operations</a></li>
</ul>
</li>
<li><a href="#undef-shl-overflow">Exact Left Shift Overflow</a></li>
<li><a href="#undef-shr-overflow">Exact Right Shift Overflow</a></li>
<li><a href="#undef-division-by-zero">Division by Zero</a></li>
<li><a href="#undef-remainder-division-by-zero">Remainder Division by Zero</a></li>
<li><a href="#undef-exact-division-remainder">Exact Division Remainder</a></li>
<li><a href="#undef-slice-widen-remainder">Slice Widen Remainder</a></li>
<li><a href="#undef-attempt-unwrap-null">Attempt to Unwrap Null</a></li>
<li><a href="#undef-attempt-unwrap-error">Attempt to Unwrap Error</a></li>
<li><a href="#undef-invalid-error-code">Invalid Error Code</a></li>
<li><a href="#undef-invalid-enum-cast">Invalid Enum Cast</a></li>
<li><a href="#undef-incorrect-pointer-alignment">Incorrect Pointer Alignment</a></li>
<li><a href="#undef-bad-union-field">Wrong Union Field Access</a></li>
</ul>
</li>
<li><a href="#memory">Memory</a></li>
<li><a href="#compile-variables">Compile Variables</a></li>
<li><a href="#root-source-file">Root Source File</a></li>
<li><a href="#zig-test">Zig Test</a></li>
<li><a href="#zig-build-system">Zig Build System</a></li>
<li><a href="#c">C</a>
<ul>
<li><a href="#c-type-primitives">C Type Primitives</a></li>
<li><a href="#c-string-literals">C String Literals</a></li>
<li><a href="#c-import">Import from C Header File</a></li>
<li><a href="#mixing-object-files">Mixing Object Files</a></li>
</ul>
</li>
<li><a href="#targets">Targets</a></li>
<li><a href="#style-guide">Style Guide</a>
<ul>
<li><a href="#style-guide-whitespace">Whitespace</a></li>
<li><a href="#style-guide-names">Names</a></li>
<li><a href="#style-guide-examples">Examples</a></li>
</ul>
</li>
<li><a href="#grammar">Grammar</a></li>
<li><a href="#zen">Zen</a></li>
</ul>
</div>
<div id="contents">
<h1 id="introduction">Zig Documentation</h1>
<p>
Zig is an open-source programming language designed for <strong>robustness</strong>,
<strong>optimality</strong>, and <strong>clarity</strong>.
</p>
<ul>
<li><strong>Robust</strong> - behavior is correct even for edge cases such as out of memory.</li>
<li><strong>Optimal</strong> - write programs the best way they can behave and perform.</li>
<li><strong>Clear</strong> - precisely communicate your intent to the compiler and other programmers. The language imposes a low overhead to reading code.</li>
</ul>
<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>
If you search for something specific in this documentation and do not find it,
please <a href="https://github.com/zig-lang/www.ziglang.org/issues/new?title=I%20searched%20for%20___%20in%20the%20docs%20and%20didn%27t%20find%20it">file an issue</a> or <a href="https://webchat.freenode.net/?channels=%23zig">say something on IRC</a>.
</p>
<h2 id="hello-world">Hello World</h2>
<pre><code class="zig">const io = @import("std").io;
pub fn main() -> %void {
// If this program is run without stdout attached, exit with an error.
var stdout_file = %return io.getStdOut();
const stdout = &stdout_file.out_stream;
// If this program encounters pipe failure when printing to stdout, exit
// with an error.
%return stdout.print("Hello, world!\n");
}</code></pre>
<pre><code class="sh">$ zig build-exe hello.zig
$ ./hello
Hello, world!</code></pre>
<p>
Usually you don't want to write to stdout. You want to write to stderr. And you
don't care if it fails. It's more like a <em>warning message</em> that you want
to emit. For that you can use a simpler API:
</p>
<pre><code class="zig">const warn = @import("std").debug.warn;
pub fn main() -> %void {
warn("Hello, world!\n");
}</code></pre>
<p>See also:</p>
<ul>
<li><a href="#values">Values</a></li>
<li><a href="#builtin-import">@import</a></li>
<li><a href="#errors">Errors</a></li>
<li><a href="#root-source-file">Root Source File</a></li>
</ul>
<h2 id="values">Values</h2>
<pre><code class="zig">const warn = @import("std").debug.warn;
const os = @import("std").os;
const assert = @import("std").debug.assert;
// error declaration, makes `error.ArgNotFound` available
error ArgNotFound;
pub fn main() -> %void {
// integers
const one_plus_one: i32 = 1 + 1;
warn("1 + 1 = {}\n", one_plus_one);
// floats
const seven_div_three: f32 = 7.0 / 3.0;
warn("7.0 / 3.0 = {}\n", seven_div_three);
// boolean
warn("{}\n{}\n{}\n",
true and false,
true or false,
!true);
// nullable
var nullable_value: ?[]const u8 = null;
assert(nullable_value == null);
warn("\nnullable 1\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(nullable_value)), nullable_value);
nullable_value = "hi";
assert(nullable_value != null);
warn("\nnullable 2\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(nullable_value)), nullable_value);
// error union
var number_or_error: %i32 = error.ArgNotFound;
warn("\nerror union 1\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(number_or_error)), number_or_error);
number_or_error = 1234;
warn("\nerror union 2\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(number_or_error)), number_or_error);
}</code></pre>
<pre><code class="sh">$ zig build-exe values.zig
$ ./values
1 + 1 = 2
7.0 / 3.0 = 2.333333
false
true
false
nullable 1
type: ?[]const u8
value: null
nullable 2
type: ?[]const u8
value: hi
error union 1
type: %i32
value: error.ArgNotFound
error union 2
type: %i32
value: 1234</code></pre>
<h3 id="primitive-types">Primitive Types</h2>
<table>
<tr>
<th>
Name
</th>
<th>
C Equivalent
</th>
<th>
Description
</th>
</tr>
<tr>
<td><code>i2</code></td>
<td><code>(none)</code></td>
<td>signed 2-bit integer</td>
</tr>
<tr>
<td><code>u2</code></td>
<td><code>(none)</code></td>
<td>unsigned 2-bit integer</td>
</tr>
<tr>
<td><code>i3</code></td>
<td><code>(none)</code></td>
<td>signed 3-bit integer</td>
</tr>
<tr>
<td><code>u3</code></td>
<td><code>(none)</code></td>
<td>unsigned 3-bit integer</td>
</tr>
<tr>
<td><code>i4</code></td>
<td><code>(none)</code></td>
<td>signed 4-bit integer</td>
</tr>
<tr>
<td><code>u4</code></td>
<td><code>(none)</code></td>
<td>unsigned 4-bit integer</td>
</tr>
<tr>
<td><code>i5</code></td>
<td><code>(none)</code></td>
<td>signed 5-bit integer</td>
</tr>
<tr>
<td><code>u5</code></td>
<td><code>(none)</code></td>
<td>unsigned 5-bit integer</td>
</tr>
<tr>
<td><code>i6</code></td>
<td><code>(none)</code></td>
<td>signed 6-bit integer</td>
</tr>
<tr>
<td><code>u6</code></td>
<td><code>(none)</code></td>
<td>unsigned 6-bit integer</td>
</tr>
<tr>
<td><code>i7</code></td>
<td><code>(none)</code></td>
<td>signed 7-bit integer</td>
</tr>
<tr>
<td><code>u7</code></td>
<td><code>(none)</code></td>
<td>unsigned 7-bit integer</td>
</tr>
<tr>
<td><code>i8</code></td>
<td><code>int8_t</code></td>
<td>signed 8-bit integer</td>
</tr>
<tr>
<td><code>u8</code></td>
<td><code>uint8_t</code></td>
<td>unsigned 8-bit integer</td>
</tr>
<tr>
<td><code>i16</code></td>
<td><code>int16_t</code></td>
<td>signed 16-bit integer</td>
</tr>
<tr>
<td><code>u16</code></td>
<td><code>uint16_t</code></td>
<td>unsigned 16-bit integer</td>
</tr>
<tr>
<td><code>i32</code></td>
<td><code>int32_t</code></td>
<td>signed 32-bit integer</td>
</tr>
<tr>
<td><code>u32</code></td>
<td><code>uint32_t</code></td>
<td>unsigned 32-bit integer</td>
</tr>
<tr>
<td><code>i64</code></td>
<td><code>int64_t</code></td>
<td>signed 64-bit integer</td>
</tr>
<tr>
<td><code>u64</code></td>
<td><code>uint64_t</code></td>
<td>unsigned 64-bit integer</td>
</tr>
<tr>
<td><code>i128</code></td>
<td><code>__int128</code></td>
<td>signed 128-bit integer</td>
</tr>
<tr>
<td><code>u128</code></td>
<td><code>unsigned __int128</code></td>
<td>unsigned 128-bit integer</td>
</tr>
<tr>
<td><code>isize</code></td>
<td><code>intptr_t</code></td>
<td>signed pointer sized integer</td>
</tr>
<tr>
<td><code>usize</code></td>
<td><code>uintptr_t</code></td>
<td>unsigned pointer sized integer</td>
</tr>
<tr>
<td><code>c_short</code></td>
<td><code>short</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_ushort</code></td>
<td><code>unsigned short</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_int</code></td>
<td><code>int</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_uint</code></td>
<td><code>unsigned int</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_long</code></td>
<td><code>long</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_ulong</code></td>
<td><code>unsigned long</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_longlong</code></td>
<td><code>long long</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_ulonglong</code></td>
<td><code>unsigned long long</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_longdouble</code></td>
<td><code>long double</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>c_void</code></td>
<td><code>void</code></td>
<td>for ABI compatibility with C</td>
</tr>
<tr>
<td><code>f32</code></td>
<td><code>float</code></td>
<td>32-bit floating point (23-bit mantissa)</td>
</tr>
<tr>
<td><code>f64</code></td>
<td><code>double</code></td>
<td>64-bit floating point (52-bit mantissa)</td>
</tr>
<tr>
<td><code>f128</code></td>
<td>(none)</td>
<td>128-bit floating point (112-bit mantissa)</td>
</tr>
<tr>
<td><code>bool</code></td>
<td><code>bool</code></td>
<td><code>true</code> or <code>false</code></td>
</tr>
<tr>
<td><code>void</code></td>
<td>(none)</td>
<td>0 bit type</td>
</tr>
<tr>
<td><code>noreturn</code></td>
<td>(none)</td>
<td>the type of <code>break</code>, <code>continue</code>, <code>goto</code>, <code>return</code>, <code>unreachable</code>, and <code>while (true) {}</code></td>
</tr>
<tr>
<td><code>type</code></td>
<td>(none)</td>
<td>the type of types</td>
</tr>
<tr>
<td><code>error</code></td>
<td>(none)</td>
<td>an error code</td>
</tr>
</table>
<p>See also:</p>
<ul>
<li><a href="#integers">Integers</a></li>
<li><a href="#floats">Floats</a></li>
<li><a href="#void">void</a></li>
<li><a href="#errors">Errors</a></li>
</ul>
<h3 id="primitive-values">Primitive Values</h3>
<table>
<tr>
<th>
Name
</th>
<th>
Description
</th>
</tr>
<tr>
<td><code>true</code> and <code>false</code></td>
<td><code>bool</code> values</td>
</tr>
<tr>
<td><code>null</code></td>
<td>used to set a nullable type to <code>null</code></td>
</tr>
<tr>
<td><code>undefined</code></td>
<td>used to leave a value unspecified</td>
</tr>
<tr>
<td><code>this</code></td>
<td>refers to the thing in immediate scope</td>
</tr>
</table>
<p>See also:</p>
<ul>
<li><a href="#nullables">Nullables</a></li>
<li><a href="#this">this</a></li>
</ul>
<h3 id="string-literals">String Literals</h3>
<pre><code class="zig">const assert = @import("std").debug.assert;
const mem = @import("std").mem;
test "string literals" {
// In Zig a string literal is an array of bytes.
const normal_bytes = "hello";
assert(@typeOf(normal_bytes) == [5]u8);
assert(normal_bytes.len == 5);
assert(normal_bytes[1] == 'e');
assert('e' == '\x65');
assert(mem.eql(u8, "hello", "h\x65llo"));
// A C string literal is a null terminated pointer.
const null_terminated_bytes = c"hello";
assert(@typeOf(null_terminated_bytes) == &const u8);
assert(null_terminated_bytes[5] == 0);
}</code></pre>
<pre><code class="sh">$ zig test string_literals.zig
Test 1/1 string literals...OK</code></pre>
<p>See also:</p>
<ul>
<li><a href="#arrays">Arrays</a></li>
<li><a href="#zig-test">Zig Test</a></li>
</ul>
<h4 id="string-literal-escapes">Escape Sequences</h4>
<table>
<tr>
<th>
Escape Sequence
</th>
<th>
Name
</th>
</tr>
<tr>
<td><code>\n</code></td>
<td>Newline</td>
</tr>
<tr>
<td><code>\r</code></td>
<td>Carriage Return</td>
</tr>
<tr>
<td><code>\t</code></td>
<td>Tab</td>
</tr>
<tr>
<td><code>\\</code></td>
<td>Backslash</td>
</tr>
<tr>
<td><code>\'</code></td>
<td>Single Quote</td>
</tr>
<tr>
<td><code>\"</code></td>
<td>Double Quote</td>
</tr>
<tr>
<td><code>\xNN</code></td>
<td>hexadecimal 8-bit character code (2 digits)</td>
</tr>
<tr>
<td><code>\uNNNN</code></td>
<td>hexadecimal 16-bit Unicode character code UTF-8 encoded (4 digits)</td>
</tr>
<tr>
<td><code>\UNNNNNN</code></td>
<td>hexadecimal 24-bit Unicode character code UTF-8 encoded (6 digits)</td>
</tr>
</table>
<p>Note that the maximum valid Unicode point is <code>0x10ffff</code>.</p>
<h4 id="multiline-string-literals">Multiline String Literals</h4>
<p>
Multiline string literals have no escapes and can span across multiple lines.
To start a multiline string literal, use the <code>\\</code> token. Just like a comment,
the string literal goes until the end of the line. The end of the line is
not included in the string literal.
However, if the next line begins with <code>\\</code> then a newline is appended and
the string literal continues.
</p>
<pre><code class="zig">const hello_world_in_c =
\\#include <stdio.h>
\\
\\int main(int argc, char **argv) {
\\ printf("hello world\n");
\\ return 0;
\\}
;</code></pre>
<p>
For a multiline C string literal, prepend <code>c</code> to each <code>\\</code>:
</p>
<pre><code class="zig">const c_string_literal =
c\\#include <stdio.h>
c\\
c\\int main(int argc, char **argv) {
c\\ printf("hello world\n");
c\\ return 0;
c\\}
;</code></pre>
<p>
In this example the variable <code>c_string_literal</code> has type <code>&const char</code> and
has a terminating null byte.
</p>
<p>See also:</p>
<ul>
<li><a href="#builtin-embedFile">@embedFile</a></li>
</ul>
<h3 id="values-assignment">Assignment</h3>
<p>Use <code>const</code> to assign a value to an identifier:</p>
<pre><code class="zig">const x = 1234;
fn foo() {
// It works at global scope as well as inside functions.
const y = 5678;
// Once assigned, an identifier cannot be changed.
y += 1;
}
test "assignment" {
foo();
}</code></pre>
<pre><code class="sh">$ zig test test.zig
test.zig:8:7: error: cannot assign to constant
y += 1;
^</code></pre>
<p>If you need a variable that you can modify, use <code>var</code>:</p>
<pre><code class="zig">const assert = @import("std").debug.assert;
test "var" {
var y: i32 = 5678;
y += 1;
assert(y == 5679);
}</code></pre>
<pre><code class="sh">$ zig test test.zig
Test 1/1 assignment...OK</code></pre>
<p>Variables must be initialized:</p>
<pre><code class="zig">test "initialization" {
var x: i32;
x = 1;
}</code></pre>
<pre><code class="sh">$ zig test test.zig
test.zig:3:5: error: variables must be initialized
var x: i32;
^</code></pre>
<p>Use <code>undefined</code> to leave variables uninitialized:</p>
<pre><code class="zig">const assert = @import("std").debug.assert;
test "init with undefined" {
var x: i32 = undefined;
x = 1;
assert(x == 1);
}</code></pre>
<pre><code class="sh">$ zig test test.zig
Test 1/1 init with undefined...OK</code></pre>
<h2 id="integers">Integers</h2>
<h3 id="integer-literals">Integer Literals</h3>
<pre><code class="zig">const decimal_int = 98222;
const hex_int = 0xff;
const another_hex_int = 0xFF;
const octal_int = 0o755;
const binary_int = 0b11110000;</code></pre>
<h3 id="runtime-integer-values">Runtime Integer Values</h3>
<p>
Integer literals have no size limitation, and if any undefined behavior occurs,
the compiler catches it.
</p>
<p>
However, once an integer value is no longer known at compile-time, it must have a
known size, and is vulnerable to undefined behavior.
</p>
<pre><code class="zig">fn divide(a: i32, b: i32) -> i32 {
return a / b;
}</code></pre>
<p>
In this function, values <code>a</code> and <code>b</code> are known only at runtime,
and thus this division operation is vulnerable to both integer overflow and
division by zero.
</p>
<p>
Operators such as <code>+</code> and <code>-</code> cause undefined behavior on
integer overflow. Also available are operations such as <code>+%</code> and
<code>-%</code> which are defined to have wrapping arithmetic on all targets.
</p>
<p>See also:</p>
<ul>
<li><a href="#undef-integer-overflow">Integer Overflow</a></li>
<li><a href="#undef-division-by-zero">Division By Zero</a></li>
<li><a href="#undef-int-overflow-wrap">Wrapping Operations</a></li>
</ul>
<h2 id="floats">Floats</h2>
<h3 id="float-literals">Float Literals</h3>
<pre><code class="zig">const floating_point = 123.0E+77;
const another_float = 123.0;
const yet_another = 123.0e+77;
const hex_floating_point = 0x103.70p-5;
const another_hex_float = 0x103.70;
const yet_another_hex_float = 0x103.70P-5;</code></pre>
<h3 id="float-operations">Floating Point Operations</h3>
<p>By default floating point operations use <code>Optimized</code> mode,
but you can switch to <code>Strict</code> mode on a per-block basis:</p>
<p>foo.zig</p>
<pre><code class="zig">const builtin = @import("builtin");
const big = f64(1 << 40);
export fn foo_strict(x: f64) -> f64 {
@setFloatMode(this, builtin.FloatMode.Strict);
return x + big - big;
}
export fn foo_optimized(x: f64) -> f64 {
return x + big - big;
}</code></pre>
<p>test.zig</p>
<pre><code class="zig">const warn = @import("std").debug.warn;
extern fn foo_strict(x: f64) -> f64;
extern fn foo_optimized(x: f64) -> f64;
pub fn main() -> %void {
const x = 0.001;
warn("optimized = {}\n", foo_optimized(x));
warn("strict = {}\n", foo_strict(x));
}</code></pre>
<p>For this test we have to separate code into two object files -
otherwise the optimizer figures out all the values at compile-time,
which operates in strict mode.</p>
<pre><code class="sh">$ zig build-obj foo.zig --release-fast
$ zig build-exe test.zig --object foo.o
$ ./test
optimized = 1.0e-2
strict = 9.765625e-3</code></pre>
<p>See also:</p>
<ul>
<li><a href="#builtin-setFloatMode">@setFloatMode</a></li>
<li><a href="#undef-division-by-zero">Division By Zero</a></li>
</ul>
<h2 id="operators">Operators</h2>
<h3 id="operators-table">Table of Operators</h2>
<table>
<tr>
<th>
Syntax
</th>
<th>
Relevant Types
</th>
<th>
Description
</th>
<th>
Example
</th>
</tr>
<tr>
<td><pre><code class="zig">a + b
a += b</code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
<li><a href="#floats">Floats</a></li>
</ul>
</td>
<td>Addition.
<ul>
<li>Can cause <a href="#undef-integer-overflow">overflow</a> for integers.</li>
</ul>
</td>
<td>
<pre><code class="zig">2 + 5 == 7</code></pre>
</td>
</tr>
<tr>
<td><pre><code class="zig">a +% b
a +%= b</code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
</ul>
</td>
<td>Wrapping Addition.
<ul>
<li>Guaranteed to have twos-complement wrapping behavior.</li>
</ul>
</td>
<td>
<pre><code class="zig">u32(@maxValue(u32)) +% 1 == 0</code></pre>
</td>
</tr>
<tr>
<td><pre><code class="zig">a - b
a -= b</code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
<li><a href="#floats">Floats</a></li>
</ul>
</td>
<td>Subtraction.
<ul>
<li>Can cause <a href="#undef-integer-overflow">overflow</a> for integers.</li>
</ul>
</td>
<td>
<pre><code class="zig">2 - 5 == -3</code></pre>
</td>
</tr>
<tr>
<td><pre><code class="zig">a -% b
a -%= b</code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
</ul>
</td>
<td>Wrapping Subtraction.
<ul>
<li>Guaranteed to have twos-complement wrapping behavior.</li>
</ul>
</td>
<td>
<pre><code class="zig">u32(0) -% 1 == @maxValue(u32)</code></pre>
</td>
</tr>
<tr>
<td><pre><code class="zig">-a<code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
<li><a href="#floats">Floats</a></li>
</ul>
</td>
<td>
Negation.
<ul>
<li>Can cause <a href="#undef-integer-overflow">overflow</a> for integers.</li>
</ul>
</td>
<td>
<pre><code class="zig">-1 == 0 - 1</code></pre>
</td>
</tr>
<tr>
<td><pre><code class="zig">-%a<code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
</ul>
</td>
<td>
Wrapping Negation.
<ul>
<li>Guaranteed to have twos-complement wrapping behavior.</li>
</ul>
</td>
<td>
<pre><code class="zig">-%i32(@minValue(i32)) == @minValue(i32)</code></pre>
</td>
</tr>
<tr>
<td><pre><code class="zig">a * b
a *= b</code></pre></td>
<td>
<ul>
<li><a href="#integers">Integers</a></li>
<li><a href="#floats">Floats</a></li>
</ul>