148 lines
13 KiB
HTML
148 lines
13 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>std::midpoint</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_midpoint skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>midpoint</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-numeric.html">numeric</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><a href="cpp-header-numeric.html"><numeric></a></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span><br />
|
|
<span class="kw4">constexpr</span> T midpoint<span class="br0">(</span>T a, T b<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span><br />
|
|
<span class="kw4">constexpr</span> T<span class="sy2">*</span> midpoint<span class="br0">(</span>T<span class="sy2">*</span> a, T<span class="sy2">*</span> b<span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>计算整数、浮点或指针 <code>a</code> 与 <code>b</code> 的中点。</p>
|
|
<div class="t-li1"><span class="t-li">1)</span> 此重载仅若 <code>T</code> 为 <code>bool</code> 以外的算术类型才参与重载决议。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 此重载仅若 <code>T</code> 为对象类型才参与重载决议。若 <code>T</code> 为<a href="cpp-language-type.html#.E4.B8.8D.E5.AE.8C.E6.95.B4.E7.B1.BB.E5.9E.8B">不完整类型</a>则此重载的使用为谬构。</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>a, b</td>
|
|
<td>-</td>
|
|
<td>整数、浮点或指针值</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<div class="t-li1"><span class="t-li">1)</span> <code>a</code> 与 <code>b</code> 和的一半。不出现上溢。若 <code>a</code> 与 <code>b</code> 拥有整数类型而和为奇数，则向 <code>a</code> 取整结果。若 <code>a</code> 与 <code>b</code> 拥有浮点类型，则至多出现一次不准确运算。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 若 <code>a</code> 与 <code>b</code> 分别指向（就<a href="cpp-language-operator_arithmetic.html#.E5.8A.A0.E6.B3.95.E6.80.A7.E8.BF.90.E7.AE.97.E7.AC.A6">指针算术</a>目的而言的）同一数组对象 <code>x</code> 的 <code>x[i]</code> 与 <code>x[j]</code> ，则返回指向 <code>x[i+(j-i)/2]</code> （或等价地为 <code>x[std::midpoint(i, j)]</code> ）的指针，其中除法向零取整。若 <code>a</code> 与 <code>b</code> 不指向同一数组对象，则行为未定义。</div>
|
|
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
|
|
<p>不抛异常。</p>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p>重载 <span class="t-v">(2)</span> 在常见平台上能简单地实现为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> a <span class="sy2">+</span> <span class="br0">(</span>b <span class="sy2">-</span> a<span class="br0">)</span> <span class="sy2">/</span> <span class="nu0">2</span><span class="sy4">;</span></span></span> 。然而不保证这种实现是可移植的，因为可以有一些平台上，可在其上创建元素数大于 <span class="t-lc"><a href="cpp-types-climits.html">PTRDIFF_MAX</a></span> 的数组，从而即使 <code>b</code> 与 <code>a</code> 均指向同一数组的元素 <span class="t-c"><span class="mw-geshi cpp source-cpp">b <span class="sy2">-</span> a</span></span> 亦可导致未定义行为。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <cstdint></span>
|
|
<span class="co2">#include <limits></span>
|
|
<span class="co2">#include <numeric></span>
|
|
<span class="co2">#include <iostream></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-types-integer.html"><span class="kw122">std::<span class="me2">uint32_t</span></span></a> a <span class="sy1">=</span> <a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span><a href="cpp-types-integer.html"><span class="kw122">std::<span class="me2">uint32_t</span></span></a><span class="sy1">></span><span class="sy4">::</span><span class="me2">max</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-types-integer.html"><span class="kw122">std::<span class="me2">uint32_t</span></span></a> b <span class="sy1">=</span> <a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span><a href="cpp-types-integer.html"><span class="kw122">std::<span class="me2">uint32_t</span></span></a><span class="sy1">></span><span class="sy4">::</span><span class="me2">max</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">2</span><span class="sy4">;</span>
|
|
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"a: "</span> <span class="sy1"><<</span> a <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
|
|
<span class="sy1"><<</span> <span class="st0">"b: "</span> <span class="sy1"><<</span> b <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
|
|
<span class="sy1"><<</span> <span class="st0">"Incorrect (overflow and wrapping): "</span> <span class="sy1"><<</span> <span class="br0">(</span>a <span class="sy2">+</span> b<span class="br0">)</span> <span class="sy2">/</span> <span class="nu0">2</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
|
|
<span class="sy1"><<</span> <span class="st0">"Correct: "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">midpoint</span><span class="br0">(</span>a, b<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"<span class="es1">\n</span><span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
|
|
|
|
<span class="kw4">auto</span> on_pointers <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> i, <span class="kw4">int</span> j<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw4">char</span> <span class="kw4">const</span><span class="sy2">*</span> text <span class="sy1">=</span> <span class="st0">"0123456789"</span><span class="sy4">;</span>
|
|
<span class="kw4">char</span> <span class="kw4">const</span><span class="sy2">*</span> p <span class="sy1">=</span> text <span class="sy2">+</span> i<span class="sy4">;</span>
|
|
<span class="kw4">char</span> <span class="kw4">const</span><span class="sy2">*</span> q <span class="sy1">=</span> text <span class="sy2">+</span> j<span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"std::midpoint('"</span> <span class="sy1"><<</span> <span class="sy2">*</span>p <span class="sy1"><<</span> <span class="st0">"', '"</span> <span class="sy1"><<</span> <span class="sy2">*</span>q <span class="sy1"><<</span> <span class="st0">"'): '"</span>
|
|
<span class="sy1"><<</span> <span class="sy2">*</span>std<span class="sy4">::</span><span class="me2">midpoint</span><span class="br0">(</span>p, q<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"'<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
on_pointers<span class="br0">(</span><span class="nu0">2</span>, <span class="nu0">4</span><span class="br0">)</span><span class="sy4">;</span>
|
|
on_pointers<span class="br0">(</span><span class="nu0">2</span>, <span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span>
|
|
on_pointers<span class="br0">(</span><span class="nu0">5</span>, <span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span>
|
|
on_pointers<span class="br0">(</span><span class="nu0">2</span>, <span class="nu0">6</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">a: 4294967295
|
|
b: 4294967293
|
|
Incorrect (overflow and wrapping): 2147483646
|
|
Correct: 4294967294
|
|
|
|
std::midpoint('2', '4'): '3'
|
|
std::midpoint('2', '5'): '3'
|
|
std::midpoint('5', '2'): '4'
|
|
std::midpoint('2', '6'): '4'</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
|
|
<div class="t-ref-std-c++20">
|
|
<ul>
|
|
<li>C++20 标准（ISO/IEC 14882:2020）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>25.10.15 Midpoint [numeric.ops.midpoint]</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-numeric-lerp.html"><span class="t-lines"><span>lerp</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>线性插值函数<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|