📄 csdn_文档中心_指针的艺术.htm
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<TD align=middle bgColor=#003399><FONT color=#ffffff>关键字</FONT></TD>
<TD width=500> 指针</TD></TR>
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<P align=center class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center"><B><SPAN
style="FONT-FAMILY: 宋体; FONT-SIZE: 14pt; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指针的艺术</SPAN></B><B><SPAN
lang=EN-US
style="FONT-SIZE: 14pt; mso-bidi-font-size: 12.0pt"><?xml:namespace
prefix = o ns = "urn:schemas-microsoft-com:office:office"
/><o:p></o:p></SPAN></B></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT size=3><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">作为一个</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'">程序员，指针的直接操作内存，在数据操作方面有着速度快，节约内存等优点，仍是很多</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'">程序员的最爱。指针是一把双刃剑，用好了它，你就会发现指针有多么的方便，反之，你可能就头疼了，往往会出现意想不到的问题。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3>一．什么是指针：</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3>其实指针就像是其它变量一样，所不同的是一般的变量包含的是实际的真实的数据，而指针是一个指示器，它告诉程序在内存的哪块区域可以找到数据。</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3>这是一个非常重要的概念，有很多程序和算法都是围绕指针而设计的，如链表。</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT size=3><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指针是一个数据类型，本身也需要占用四个字节的存储空间。所以用</SPAN><SPAN
lang=EN-US>sizeof(void*)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">获得的值为</SPAN><SPAN
lang=EN-US>4</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3>二．指针的定义</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US><SPAN
style="mso-tab-count: 1">
</SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">看如下的例子：</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>int *pNumber;</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US><SPAN
style="mso-tab-count: 1">
</SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">这样就定义了</SPAN><SPAN
lang=EN-US>int</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">类型的指针。</SPAN></FONT></P>
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lang=EN-US><SPAN
style="mso-tab-count: 1">
</SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指针变量名称以</SPAN><SPAN
lang=EN-US>p</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">为首字符，这是程序员通常在定义指针时的一个习惯，以提高便程序的阅读性，表示这是个指针。另外，虽然</SPAN><SPAN
lang=EN-US>int* pNumber</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>int *pNumber</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是相同的，但是使用后一种的编程风格更好一些。比如：</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US>int *pNumber1,*pNumber2;</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">表示定义两个指针，</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'">号和变量靠近；反之，我们可能会定义成</SPAN><SPAN
lang=EN-US>int* pNumber1,pNumber2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，这将是一个错误的定义，</SPAN><SPAN
lang=EN-US>pNumber2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">就不是指针了。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3>三．指针的优点</FONT></SPAN><SPAN lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt"><BR><FONT
size=3>a.</FONT></SPAN><FONT size=3><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">为函数提供修改调用变元的手段；</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">b.</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">支持</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">C++</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">动态分配子程序</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">c.</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">可以改善某些子程序的效率</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">d.</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">为动态数据结构（如二叉树、链表）提供支持</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt"><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">四、指针赋值及转换：</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">a.</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">同类型直接赋值，异类型要进行转换。</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">b.</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">强制转换：可以把表达式结果硬性转换为指定类型</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">c.char *
p;(int *)p </SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">把</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">p</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">强制转换为</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">int</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">型，记住转换过程中要注意两个类型的大小，大转小时可能会有数据丢失（如</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">int</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">到</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">double</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">d.</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">涉及</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">void
*</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">:
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT size=3><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">c
</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">void
*</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">类型可赋值给任何类型的指针，反之亦然</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT size=3><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">c++
</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中都需要强制转换</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT size=3><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">void
*</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"> 可看作无穷大能接纳任何类型赋值，反之不行</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">int * p
=9;void * t= p</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">（正确）</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">;p=t(</SPAN><SPAN
style="COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-size: 9.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">错误</SPAN><SPAN
lang=EN-US style="COLOR: black; mso-bidi-font-size: 9.0pt">)
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
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