utf-8, unicode, gb2312格式串转换之-c语言版 - 平凡中的不平凡 - 博客园.htm

最为全面的c++内存模型探秘。不管是初学者还是老手

style="COLOR: #000000">&nbsp;B();<BR>}</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>2）强制类型转化，即我们常说的C风格的类型转化，基本上可以用于所有的转化，但是没有意义的转化除外，但是父子类，兄弟间的转化没有类型检查可能导致运行是错误。<BR>适用：<BR><SPAN 
style="COLOR: #ff0000">第一，基本类型转化；<BR>第二，void*到其他指针的转化；<BR>第三，去除const；<BR>第五，函数指针的转化；<BR>第六，父子类转化，但是多重继承和兄弟转化，可能有运行时错误，没有类型检查；<BR>第七，任何两个类，但是没有实际意义，运行可能出错；<BR>第八，不能用于没有意义的转化，严厉禁止，例如，你不能用static_cast象用C风格的类型转换一样把struct转换成int类型，或者把double类型转换成指针类型；<BR>第九，在C++一般更推荐新加的static_cast，const_cast，dynamic_cast和reinterpret_cast转化方式；</SPAN></P>
<P>实例：</P>
<DIV class=cnblogs_code><IMG id=Code_Closed_Image_150722 style="DISPLAY: none" 
onclick="this.style.display='none'; document.getElementById('Code_Closed_Text_150722').style.display='none'; document.getElementById('Code_Open_Image_150722').style.display='inline'; document.getElementById('Code_Open_Text_150722').style.display='inline';" 
height=16 
src="UTF-8, Unicode, GB2312格式串转换之-C语言版 - 平凡中的不平凡 - 博客园.files/ContractedBlock.gif" 
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onclick="this.style.display='none'; document.getElementById('Code_Open_Text_150722').style.display='none'; getElementById('Code_Closed_Image_150722').style.display='inline'; getElementById('Code_Closed_Text_150722').style.display='inline';" 
height=16 
src="UTF-8, Unicode, GB2312格式串转换之-C语言版 - 平凡中的不平凡 - 博客园.files/ExpandedBlockStart.gif" 
width=11 align=top><SPAN class=cnblogs_code_Collapse 
id=Code_Closed_Text_150722>Code</SPAN><SPAN id=Code_Open_Text_150722><BR><!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--><SPAN 
style="COLOR: #0000ff">class</SPAN><SPAN 
style="COLOR: #000000">&nbsp;CDummy&nbsp;<BR>{<BR></SPAN><SPAN 
style="COLOR: #0000ff">public</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;CDummy(</SPAN><SPAN 
style="COLOR: #0000ff">float</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">float</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;i&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;j&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;y;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR></SPAN><SPAN 
style="COLOR: #0000ff">private</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">float</SPAN><SPAN 
style="COLOR: #000000">&nbsp;i,j;<BR>};<BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">class</SPAN><SPAN 
style="COLOR: #000000">&nbsp;CAddition&nbsp;<BR>{<BR></SPAN><SPAN 
style="COLOR: #0000ff">public</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;CAddition&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;a,&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;b)&nbsp;{&nbsp;x</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">a;&nbsp;y</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">b;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;result()&nbsp;{&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x</SPAN><SPAN style="COLOR: #000000">+</SPAN><SPAN 
style="COLOR: #000000">y;}<BR></SPAN><SPAN 
style="COLOR: #0000ff">private</SPAN><SPAN 
style="COLOR: #000000">:<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;x,y;<BR>};<BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Testing()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;std::cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">Testing</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;std::endl;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800080">10</SPAN><SPAN 
style="COLOR: #000000">;<BR>}<BR><BR></SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ExplicitCast()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">double</SPAN><SPAN 
style="COLOR: #000000">&nbsp;r&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">double</SPAN><SPAN style="COLOR: #000000">)</SPAN><SPAN 
style="COLOR: #800080">1</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">/</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #800080">3</SPAN><SPAN 
style="COLOR: #000000">;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">pi&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">(</SPAN><SPAN 
style="COLOR: #800080">10</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pV;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pV&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pi;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">pj&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">)pV;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;或&nbsp;int&nbsp;*pj&nbsp;=&nbsp;int*(pV);</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000"><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">const</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pa&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">(</SPAN><SPAN 
style="COLOR: #800080">20</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pb;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pb&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">)pa;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">pb&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #800080">30</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;std::cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pa&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;std::endl;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;typedef&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">Fun)();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;Fun&nbsp;f&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(Fun)Testing;<BR>&nbsp;&nbsp;&nbsp;&nbsp;f();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;多重继承或将兄弟间的转化可能会出错<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;虽然可以正确的编译，但是运行有问题，所以我们不做没有意义的转化<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">CDummy&nbsp;d(10,30);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">CAddition&nbsp;*&nbsp;padd;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">padd&nbsp;=&nbsp;(CAddition*)&nbsp;&amp;d;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">std::cout&nbsp;&lt;&lt;&nbsp;padd-&gt;result();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;不做没有意义的转化</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #808080">///</SPAN><SPAN 
style="COLOR: #008000">/&nbsp;error</SPAN><SPAN 
style="COLOR: #808080"><BR></SPAN><SPAN 
style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">struct&nbsp;st{int&nbsp;i;&nbsp;double&nbsp;d;};<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">st&nbsp;s;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">int&nbsp;x&nbsp;=&nbsp;(int)s;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">c2440<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">double&nbsp;y&nbsp;=&nbsp;10.0;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">int&nbsp;*p&nbsp;=&nbsp;(int*)y;&nbsp;</SPAN><SPAN 
style="COLOR: #008000">//</SPAN><SPAN 
style="COLOR: #008000">&nbsp;c2440</SPAN><SPAN 
style="COLOR: #008000"><BR></SPAN><SPAN 
style="COLOR: #000000">}</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>3）static_cast在功能上基本上与C风格的类型转换一样强大，含义也一样。<BR>它也有功能上限制：<BR><SPAN 
style="COLOR: #ff0000">第一，不能兄弟间转化，父子间转化没有类型安全检查，有可能会导致运行时错误，父子兄弟的动态转化应该适用dynamic_cast；<BR>第二，不能去除const，适用专用的const_cast；<BR>第三，不能用于两个没有继承关系的类，当然实际上这样的转化也是没有意义的；<BR>第四，当然也不支持没有意义的转化，例如，你不能用static_cast象用C风格的类型转换一样把struct转换成int类型，或者把double类型转换成指针类型；</SPAN></P>
<P>4）const_cast，用来修改类型的const或volatile属性。</P>
<P>适用：<BR><SPAN 
style="COLOR: #ff0000">第一，常量指针被转化成非常量指针，并且仍然指向原来的对象；<BR>第二，常量引用被转换成非常量引用，并且仍然指向原来的对象；<BR>第三，常量对象被转换成非常量对象；</SPAN></P>
<P>实例：</P>
<P>&nbsp;</P>
<DIV class=cnblogs_code><IMG id=Code_Closed_Image_151441 style="DISPLAY: none" 
onclick="this.style.display='none'; document.getElementById('Code_Closed_Text_151441').style.display='none'; document.getElementById('Code_Open_Image_151441').style.display='inline'; document.getElementById('Code_Open_Text_151441').style.display='inline';" 
height=16 
src="UTF-8, Unicode, GB2312格式串转换之-C语言版 - 平凡中的不平凡 - 博客园.files/ContractedBlock.gif" 
width=11 align=top><IMG id=Code_Open_Image_151441 
onclick="this.style.display='none'; document.getElementById('Code_Open_Text_151441').style.display='none'; getElementById('Code_Closed_Image_151441').style.display='inline'; getElementById('Code_Closed_Text_151441').style.display='inline';" 
height=16 
src="UTF-8, Unicode, GB2312格式串转换之-C语言版 - 平凡中的不平凡 - 博客园.files/ExpandedBlockStart.gif" 
width=11 align=top><SPAN class=cnblogs_code_Collapse 
id=Code_Closed_Text_151441>Code</SPAN><SPAN id=Code_Open_Text_151441><BR><!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;ConstCastTest()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">const</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pa&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">(</SPAN><SPAN 
style="COLOR: #800080">20</SPAN><SPAN 
style="COLOR: #000000">);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pb;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pb&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;const_cast</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">*&gt;</SPAN><SPAN 
style="COLOR: #000000">(pa);<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">pb&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #800080">30</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;std::cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pa&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;std::endl;<BR>}</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>5）reinterpret_cast，此转型操作符的结果取决于编译器，用于修改操作数类型，非类型安全的转换符。<BR>适用：<BR><SPAN 
style="COLOR: #ff0000">一般不推荐使用，但是一般用来对函数指针的转化。<BR></SPAN>实例：</P>
<P>&nbsp;</P>
<DIV class=cnblogs_code><IMG id=Code_Closed_Image_151722 style="DISPLAY: none" 
onclick="this.style.display='none'; document.getElementById('Code_Closed_Text_151722').style.display='none'; document.getElementById('Code_Open_Image_151722').style.display='inline'; document.getElementById('Code_Open_Text_151722').style.display='inline';" 
height=16 
src="UTF-8, Unicode, GB2312格式串转换之-C语言版 - 平凡中的不平凡 - 博客园.files/ContractedBlock.gif" 
width=11 align=top><IMG id=Code_Open_Image_151722 
onclick="this.style.display='none'; document.getElementById('Code_Open_Text_151722').style.display='none'; getElementById('Code_Closed_Image_151722').style.display='inline'; getElementById('Code_Closed_Text_151722').style.display='inline';" 
height=16 
src="UTF-8, Unicode, GB2312格式串转换之-C语言版 - 平凡中的不平凡 - 博客园.files/ExpandedBlockStart.gif"