item_069.htm

C++程序编写规范,适合C++中级读者

     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>什么情况属于错误。</span></li>
 <li class=MsoNormal style='mso-list:l1 level1 lfo1;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>严重程度：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>每个错误的严重性或紧迫性。</span></li>
 <li class=MsoNormal style='mso-list:l1 level1 lfo1;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>检测：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>哪些代码负责检测错误。</span></li>
 <li class=MsoNormal style='mso-list:l1 level1 lfo1;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>传递：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>以何种机制在各模块之间报告和传递错误通知。</span></li>
 <li class=MsoNormal style='mso-list:l1 level1 lfo1;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>处理：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>哪些代码负责对错误进行处理。</span></li>
 <li class=MsoNormal style='mso-list:l1 level1 lfo1;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>报告：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>如何记录错误或将其报告给用户。</span></li>
</ul>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>只有在跨越不同的模块时才改变错误处理机制。</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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></b></p>

<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>自本条起，本节将集中讨论对运行时错误的处理，这些错误不是因为模块或子系统内部的编程错误而引起的。（第</span><span
lang=EN-US>68</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>条已经单独讨论了优先使用断言来标记内部的编程错误，这些全都是因为某些程序员的代码编写有误。）</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>为整个应用程序和每个模块或子系统确定一整套错误报告和处理策略，并严格遵守。每个策略应至少包含以下几点。</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>对所有策略：</span></p>

<ul style='margin-top:0cm' type=disc>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误的鉴定：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个实体（例如：每个函数，每个类，每个模块）以文档或注释，来说明该实体的内部和外部不变性。</span></li>
</ul>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>对每个函数：</span></p>

<ul style='margin-top:0cm' type=disc>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误的鉴定：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个函数以文档或注释，来说明该函数的前置和后置条件，在维护时应注意的该函数所涉及的不变性，以及该函数对出现错误时的安全性可以支持到何种程度（参见第</span><span
     lang=EN-US>71</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>72</span><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>条）。要特别注意析构函数和资源释放函数，应该总是把它们写得能够保证对它们的调用不会失败，因为如果不是这样，那么通常无法可靠地并安全地进行清理（参见第</span><span
     lang=EN-US>51</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>&nbsp;</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"'>对每个错误（请参见第</span><span lang=EN-US>70</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条中对“错误”的定义）：</span></p>

<ul style='margin-top:0cm' type=disc>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误的严重程度和类别：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个错误指定一个严重程度的等级。最好提供一种方法，能够根据特定的错误类别和等级进行微调，这样有助于远程用户协助。</span></li>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误检测：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个错误以文档或注释，说明哪些代码负责检测该错误，请遵循第</span><span lang=EN-US>70</span><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>条的建议。</span></li>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误处理：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个错误以文档或注释，说明哪些代码负责处理该错误，请遵循第</span><span lang=EN-US>74</span><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>条的建议。</span></li>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误报告：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个错误以文档或注释，说明有哪些合适的报告方法。这通常包括把错误记录在一个磁盘文件日志中，把日志打印出来，电传</span><span
     lang=EN-US>dump</span><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>文件，在万一遇到非常严重的错误时，或许还可以使用既不方便又烦人的寻呼机呼叫。</span></li>
</ul>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>对每个模块：</span></p>

<ul style='margin-top:0cm' type=disc>
 <li class=MsoNormal style='mso-list:l0 level1 lfo2;tab-stops:list 36.0pt'><i
     style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>错误的传递：</span></i><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>给每个模块（注意：是每个模块，而不是每个错误）以文档或注释，说明何种编程机制将被用于错误的传递（例如：</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"'>异常，</span><span
     lang=EN-US>COM</span><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>异常，</span><span
     lang=EN-US>CORBA</span><span style='font-family:宋体;mso-ascii-font-family:
     "Times New Roman";mso-hansi-font-family:"Times New Roman"'>异常，返回值）。</span></li>
</ul>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>我们强调只有在跨越不同的模块时才改变错误处理机制（参见第</span><span
lang=EN-US>62</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>和第</span><span lang=EN-US>63</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条）。每个模块应该在内部统一使用一种错误处理策略和机制（例如：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"'>写的模块应该在内部使用异常，参见第</span><span lang=EN-US>72</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条），并在它的接口中统一使用一种，可能与内部所使用的不同，错误处理策略和机制（例如：模块可能会提供纯粹的</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"'>，这样调用代码就可以用各种编程语言来写，模块也可能为了支持</span><span
lang=EN-US>COM</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>异常而提供一个对</span><span lang=EN-US>COM</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>的封装）。</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>如果内部和外部使用的策略不同，那么模块的所有入口函数要直接负责在它们之间进行转换。例如，在一个内部使用</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"'>异常，但是对外提供</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"'>的模块中，所有的</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"'>必须用</span><span lang=EN-US>catch(...)</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>来捕获所有的异常并将它们转换为错误码。</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>特别要注意就定义而言，回调函数和线程注入（可能）是跨模块的。每个回调函数和线程注入体应该将它们内部的错误机制转换为合适的外部接口的错误策略（参见第</span><span
lang=EN-US>62</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>条）。</span></p>

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