<span leaf=""><span class="code-snippet__comment">// ==============================================</span></span></code><code><span leaf=""><span class="code-snippet__comment">// vector [] 和 at() 全方位对比</span></span></code><code><span leaf=""><span class="code-snippet__comment">// 面试必考 + 工程避坑</span></span></code><code><span leaf=""><span class="code-snippet__comment">// ==============================================</span></span></code><code><span leaf=""><span class="code-snippet__meta">#</span><span class="code-snippet__meta"><span class="code-snippet__keyword">include</span></span><span class="code-snippet__meta"> </span><span class="code-snippet__meta"><span class="code-snippet__string"><iostream></span></span></span></code><code><span leaf=""><span class="code-snippet__meta">#</span><span class="code-snippet__meta"><span class="code-snippet__keyword">include</span></span><span class="code-snippet__meta"> </span><span class="code-snippet__meta"><span class="code-snippet__string"><vector></span></span></span></code><code><span leaf=""><span class="code-snippet__keyword">using</span> <span class="code-snippet__keyword">namespace</span> std;</span></code><code><span leaf=""><span class="code-snippet__function"><span class="code-snippet__type">int</span></span><span class="code-snippet__function"> </span><span class="code-snippet__function"><span class="code-snippet__title">main</span></span><span class="code-snippet__function"><span class="code-snippet__params">()</span></span><span class="code-snippet__function"> </span>{</span></code><code><span leaf="">    vector<<span class="code-snippet__type">int</span>> v = {<span class="code-snippet__number">10</span>, <span class="code-snippet__number">20</span>, <span class="code-snippet__number">30</span>};</span></code><code><span leaf="">    <span class="code-snippet__comment">// ==================== 1. operator[] 无越界检查 ====================</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 特点：</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 1. 不检查下标是否合法</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 2. 越界 → 未定义行为（崩溃/乱码/死机）</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 3. 速度极快（无开销）</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 4. 可读可写</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 5. 不抛异常</span></span></code><code><span leaf="">    cout << v[<span class="code-snippet__number">0</span>] << endl;    <span class="code-snippet__comment">// 正常</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// cout << v[100];      // 越界：直接崩溃/乱码，无任何提示</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// ==================== 2. at() 有越界检查 ====================</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 特点：</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 1. 强制检查下标合法性</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 2. 越界 → 抛出 out_of_range 异常</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 3. 速度稍慢（有检查开销）</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 4. 可读可写</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// 5. 安全、稳定</span></span></code><code><span leaf="">    cout << v.<span class="code-snippet__built_in">at</span>(<span class="code-snippet__number">0</span>) << endl; <span class="code-snippet__comment">// 正常</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// v.at(100);           // 越界：抛出异常，可捕获</span></span></code><code><span leaf="">    <span class="code-snippet__comment">// ==================== 3. 异常捕获演示 ====================</span></span></code><code><span leaf="">    <span class="code-snippet__keyword">try</span> {</span></code><code><span leaf="">        v.<span class="code-snippet__built_in">at</span>(<span class="code-snippet__number">999</span>);</span></code><code><span leaf="">    } <span class="code-snippet__built_in">catch</span> (<span class="code-snippet__type">const</span> out_of_range& e) {</span></code><code><span leaf="">        cout << <span class="code-snippet__string">"at() 越界异常："</span> << e.<span class="code-snippet__built_in">what</span>() << endl;</span></code><code><span leaf="">    }</span></code><code><span leaf="">    <span class="code-snippet__keyword">return</span> <span class="code-snippet__number">0</span>;</span></code><code><span leaf="">}</span></code><code><span leaf=""><span class="code-snippet__comment">// ==================== 核心总结（面试必背） ====================</span></span></code><code><span leaf=""><span class="code-snippet__comment">// 1. []   ：无检查、超快、不安全、越界崩溃、不抛异常</span></span></code><code><span leaf=""><span class="code-snippet__comment">// 2. at() ：有检查、稍慢、安全、越界抛异常、稳定</span></span></code><code><span leaf=""><span class="code-snippet__comment">// 3. 性能 ：[] > at()</span></span></code><code><span leaf=""><span class="code-snippet__comment">// 4. 安全 ：at() > []</span></span></code><code><span leaf=""><span class="code-snippet__comment">// 5. 工程：高频循环用[]，外部输入用at()</span></span>