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  <div class="section" id="incrbyfloat-key-increment">
<span id="incrbyfloat"></span><h1>INCRBYFLOAT key increment<a class="headerlink" href="#incrbyfloat-key-increment" title="Permalink to this headline">¶</a></h1>
<blockquote>
<div><div class="line-block">
<div class="line">可用版本： &gt;= 2.6.0</div>
<div class="line">时间复杂度： O(1)</div>
</div>
</div></blockquote>
<p>为键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 储存的值加上浮点数增量 <code class="docutils literal notranslate"><span class="pre">increment</span></code> 。</p>
<p>如果键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 不存在，
那么 <code class="docutils literal notranslate"><span class="pre">INCRBYFLOAT</span></code> 会先将键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 的值设为 <code class="docutils literal notranslate"><span class="pre">0</span></code> ，
然后再执行加法操作。</p>
<p>如果命令执行成功，
那么键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 的值会被更新为执行加法计算之后的新值，
并且新值会以字符串的形式返回给调用者。</p>
<p>无论是键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 的值还是增量 <code class="docutils literal notranslate"><span class="pre">increment</span></code> ，
都可以使用像 <code class="docutils literal notranslate"><span class="pre">2.0e7</span></code> 、 <code class="docutils literal notranslate"><span class="pre">3e5</span></code> 、 <code class="docutils literal notranslate"><span class="pre">90e-2</span></code> 那样的指数符号(exponential notation)来表示，
但是，
<strong>执行 INCRBYFLOAT 命令之后的值</strong>总是以同样的形式储存，
也即是，
它们总是由一个数字，
一个（可选的）小数点和一个任意长度的小数部分组成（比如 <code class="docutils literal notranslate"><span class="pre">3.14</span></code> 、 <code class="docutils literal notranslate"><span class="pre">69.768</span></code> ，诸如此类)，
小数部分尾随的 <code class="docutils literal notranslate"><span class="pre">0</span></code> 会被移除，
如果可能的话，
命令还会将浮点数转换为整数（比如 <code class="docutils literal notranslate"><span class="pre">3.0</span></code> 会被保存成 <code class="docutils literal notranslate"><span class="pre">3</span></code> ）。</p>
<p>此外，
无论加法计算所得的浮点数的实际精度有多长，
<code class="docutils literal notranslate"><span class="pre">INCRBYFLOAT</span></code> 命令的计算结果最多只保留小数点的后十七位。</p>
<p>当以下任意一个条件发生时，
命令返回一个错误：</p>
<ul class="simple">
<li><p>键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 的值不是字符串类型(因为 Redis 中的数字和浮点数都以字符串的形式保存，所以它们都属于字符串类型）；</p></li>
<li><p>键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 当前的值或者给定的增量 <code class="docutils literal notranslate"><span class="pre">increment</span></code> 不能被解释(parse)为双精度浮点数。</p></li>
</ul>
<div class="section" id="id1">
<h2>返回值<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h2>
<p>在加上增量 <code class="docutils literal notranslate"><span class="pre">increment</span></code> 之后，
键 <code class="docutils literal notranslate"><span class="pre">key</span></code> 的值。</p>
</div>
<div class="section" id="id2">
<h2>代码示例<a class="headerlink" href="#id2" title="Permalink to this headline">¶</a></h2>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">redis</span><span class="o">&gt;</span> <span class="n">GET</span> <span class="n">decimal</span>
<span class="s2">&quot;3.0&quot;</span>

<span class="n">redis</span><span class="o">&gt;</span> <span class="n">INCRBYFLOAT</span> <span class="n">decimal</span> <span class="mf">2.56</span>
<span class="s2">&quot;5.56&quot;</span>

<span class="n">redis</span><span class="o">&gt;</span> <span class="n">GET</span> <span class="n">decimal</span>
<span class="s2">&quot;5.56&quot;</span>
</pre></div>
</div>
</div>
</div>


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