📄 item_001.htm
字号:
lang=EN-US><o:p></o:p></span></i></p>
<p class=MsoNormal><span class=GramE><span lang=EN-US>void</span></span><span
lang=EN-US> Fun() {</span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span>Lock <span class=SpellE>lock</span>;</span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span class=GramE>lock</span>;</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><i style='mso-bidi-font-style:
normal'>// …<o:p></o:p></i></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>}</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><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"'>示例</span><span lang=EN-US>4</span></i><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"'>：“变量可能未经初始化就使用了”。</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>初始化该变量（参见第</span><span lang=EN-US>19</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条）。</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><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"'>示例</span><span lang=EN-US>5</span></i><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"'>：“遗漏了</span><span lang=EN-US>return</span></i><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"'>”。</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>有时候编译器会要求一条</span><span lang=EN-US>return </span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语句，即使控制流不可能到达函数的末尾（例如：无限循环，</span><span lang=EN-US>throw</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语句，其它的</span><span lang=EN-US>return</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>）。这可能是件好事，因为有时你仅仅是<i style='mso-bidi-font-style:normal'>认为</i>控制流不可能到达末尾。例如，没有</span><span
lang=EN-US>default</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>的</span><span
lang=EN-US>switch</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>语句不能很好地发现由代码的改变引起的问题，所以应该有一个</span><span
lang=EN-US>default</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>并</span><span
lang=EN-US>assert( false )</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>（参见第</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"'>和</span><span lang=EN-US>90</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条）：</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </span></i><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"'>警告：遗漏了“</span><span
lang=EN-US>return</span></i><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"'>”</span><span lang=EN-US><o:p></o:p></span></i></p>
<p class=MsoNormal><span class=SpellE><span class=GramE><span lang=EN-US>int</span></span></span><span
lang=EN-US> Fun( Color c ) {</span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span class=GramE>switch</span>( c
) {</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span><span class=GramE>case</span>
Red:<span style='mso-spacerun:yes'> </span>return 2;</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span><span class=GramE>case</span>
Green: return 0;</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span><span class=GramE>case</span>
Blue:</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span><span class=GramE>case</span>
Black: return 1;</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span>}</span></p>
<p class=MsoNormal><span lang=EN-US>}</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </span></i><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"'>新版本：消除了警告</span><span
lang=EN-US><o:p></o:p></span></i></p>
<p class=MsoNormal><span class=SpellE><span class=GramE><span lang=EN-US>int</span></span></span><span
lang=EN-US> Fun( Color c ) {</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span><span class=GramE>switch</span>(
c ) {</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'> </span><span class=GramE>case</span>
Red:<span style='mso-spacerun:yes'> </span>return 2;</span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span class=GramE>case</span> Green:
return 0;</span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span class=GramE>case</span> Blue:</span></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span class=GramE>case</span> Black:
return 1;</span></p>
<p class=MsoNormal style='tab-stops:63.0pt 297.0pt'><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span></span><span class=GramE><span
lang=EN-US style='font-family:"Arial Black"'>default</span></span><span
lang=EN-US style='font-family:"Arial Black"'>:<span style='mso-tab-count:1'> </span>assert(
!"<span class=GramE>should</span> never get here!" );</span><span
lang=EN-US><span style='mso-tab-count:1'> </span></span></p>
<p class=MsoNormal style='tab-stops:63.0pt'><span lang=EN-US><span
style='mso-tab-count:1'> </span></span><span
lang=EN-US style='font-family:"Arial Black"'>return -1; </span><i
style='mso-bidi-font-style:normal'><span lang=EN-US>// </span></i><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"'>对</span><span
lang=EN-US>!"string"</span></i><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"'>求值的结果为</span><span lang=EN-US> false</span></i></p>
<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span style='mso-spacerun:yes'>
</span>}</span></p>
<p class=MsoNormal><span lang=EN-US>}</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><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"'>示例</span><span lang=EN-US>6</span></i><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"'>：“有符号</span><span lang=EN-US>/</span></i><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"'>无符号（整数）不匹配”。</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>通常并不需要对有符号</span><span lang=EN-US>/</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>无符号整数进行比较或赋值。改变要进行比较的变量的类型，使它们一致。在最坏的情况下，加一条显式的强制类型转换（编译器总是会替你进行强制类型转换，并警你它正在这样做，所以你最好直接在代码中写清楚）。</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"'>例外</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"'>有时，编译器可能会发出一些无聊甚至是欺骗性的警告（例如：仅仅是噪音），却没有办法把它关掉，或者为了消除该警告所需的工作量太大而行不通或不值得。在这些极少的情况下，作为一个团队的决策，可以避免花时间和精力去绕开那些无聊的警告：只关闭该警告，尽可能局部性地关闭，并写下清晰的注释说明为什么需要这样做。</span></p>
</div>
</body>
</html>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -