📄 item_077.htm
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<div class=Section1>
<h3><span lang=EN-US>77. </span><span style='font-family:宋体;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial'>用</span><span lang=EN-US>vector</span><span
style='font-family:宋体;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial'>和</span><span
lang=EN-US>string</span><span style='font-family:宋体;mso-ascii-font-family:Arial;
mso-hansi-font-family:Arial'>取代数组。</span></h3>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>摘要</span></b></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>为什么要用明代的花瓶玩杂耍？要避免用</span><span
lang=EN-US>C</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>风格的数组，指针运算，以及最原始的内存管理来实现数组抽象。使用</span><span
lang=EN-US>vector</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>或</span><span lang=EN-US>string</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>不仅可以使你更轻松，还能帮助你编写更安全和伸缩性更好的软件。</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>讨论</span><a name=ch75index09></a><a name=ch75index08></a><a
name=ch75lev1sec2></a><span lang=EN-US><o:p></o:p></span></b></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>缓冲区溢出和安全隐患毫无疑问是当今软件最主要的祸根。一大令人烦火的可笑限制是由于固定长度的数组导致的，即使是在正确的限度内。其中的大多数是因为使用了原始的</span><span
lang=EN-US>C</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>风格的工具——诸如内建的数组，指针和指针运算，以及手工管理内存——来代替高层概念，比如</span><span
lang=EN-US>buffer</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>，</span><span lang=EN-US>vector</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>，或</span><span lang=EN-US>string</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>要尽量使用标准库提供的工具，而不要用</span><span
lang=EN-US>C</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>风格的数组，下面列出了一些理由：</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo4;tab-stops:list 36.0pt'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>它们可以自动地管理内存：再也不需要“比任何合理的长度更长”的大小固定的缓冲区了（“定时炸弹”是一个更精确的描述），也不需要疯狂地重新分配内存和调整指针了。</span></li>
</ul>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo4;tab-stops:list 36.0pt'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>它们具有丰富的接口：实现复杂的功能很容易，也很直观。</span></li>
</ul>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo4;tab-stops:list 36.0pt'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>它们与</span><span lang=EN-US>C</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>的内存模型兼容：可以把</span><span lang=EN-US>vector</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>和</span><span lang=EN-US>string::c_str</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>传给</span><span lang=EN-US>C API</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>——读和写当然都可以。特别是，</span><span lang=EN-US>vector</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>是</span><span lang=EN-US>C++</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>通往</span><span lang=EN-US>C</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>和其它语言的大门。（参见第</span><span lang=EN-US>76</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>和</span><span lang=EN-US>78</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条）</span></li>
</ul>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo4;tab-stops:list 36.0pt'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>它们提供了更多的检查：标准库的工具可能会实现（在调试模式下）一些能够暴露出多种内存错误的迭代器和索引操作符。当今的许多标准库实现提供了这样的调试工具——务必使用它们！（跳，而不是翻，到第</span><span
lang=EN-US>83</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>条）</span></li>
</ul>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo4;tab-stops:list 36.0pt'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>它们并没有为以上这些牺牲太多的效率：事实上是，在发行版中，如果效率和安全性不能兼得的话，</span><span
lang=EN-US>vector</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>和</span><span
lang=EN-US>string</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>更侧重于效率。尽管如此，总的来说与原始的数组和指针相比，标准库的工具为创建安全的组件提供了更好的平台。</span></li>
</ul>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo4;tab-stops:list 36.0pt'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>它们蕴含了许多优化：当今的许多标准库实现包含了各种优化，而其中的许多是像我们这样的常人从未想到过的。</span></li>
</ul>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>如果在编译期就能确定大小，那么数组是可以接受的（例如：用</span><span
lang=EN-US>float[3]</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>来表示三维空间中的点；因为要转换到四维的话无论如何都应该重新设计）。</span></p>
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