📄 csdn_文档中心_指针的艺术.htm
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lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt">e.</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'">不涉及</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'">的都要强制转换</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"><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'">五．指针和数组</SPAN><SPAN
lang=EN-US
style="COLOR: black; mso-bidi-font-size: 9.0pt"><o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText
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>不带下标的数组名返回数组的起始地址，即数组首元素的地址，所以对数组的访问可有两种方式：数组下标和指针算术。例如：</FONT></SPAN></P>
<P class=MsoBodyText
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><SPAN
lang=EN-US><FONT size=3>char* pChar;</FONT></SPAN></P>
<P class=MsoBodyText
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><SPAN
lang=EN-US><FONT size=3>char chs[100];</FONT></SPAN></P>
<P class=MsoBodyText
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT size=3><SPAN
lang=EN-US>pChar = chs;</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">这样</SPAN><SPAN
lang=EN-US>pChar</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">就指向</SPAN><SPAN
lang=EN-US>chs</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">数组的首地址。</SPAN></FONT></P>
<P class=MsoBodyText 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>六．数组与引用</FONT></SPAN></P>
<P class=MsoBodyText style="MARGIN: 0cm 0cm 0pt 21pt"><FONT
size=3><SPAN lang=EN-US>a.</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">引用只是变量的别名，而不是指向变量的指针</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'">区别于取址运算符</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'">不占内存空间，对变量引用的改变其相应的变量也会改变。</SPAN></FONT><FONT
size=3><SPAN lang=EN-US> <BR>b.</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">不能对引用使用指针间接运算符</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'">进行复引用操作</SPAN></FONT><FONT
size=3><SPAN lang=EN-US> <BR>c.</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">引用必须在声明时初始化 </SPAN><SPAN
lang=EN-US>int &c = count;(c</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>count</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的别名</SPAN><SPAN
lang=EN-US>)</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>七．指针空间的动态分配与回收</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>动态分配是指针的关键技术。它是用来在不必定义变量的情况下分配内存和让指针去指向它们。分配了内存，别忘了回收。你动态地分配了一个内存空间，可它绝不会被自动删除。也就是说，这块内存空间会一直存在，直到你告诉电脑你已经使用完了。可结果是，你并没有告诉电脑你已不再需要这块内存空间了，所以它会继续占据着内存空间造成浪费，甚至你的程序运行完毕，其它程序运行时它还存在。当这样的问题积累到一定程度，最终将导致系统崩溃。所以这是很重要的，在你用完它以后，请释放它的空间。</FONT></SPAN></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>八．实际使用指针时，容易出现的错误</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>笔者归纳出指针错误的原因有以下几点（个人经验，欢迎大家补充）：</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">．指针未初始化。</SPAN></FONT></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'">指针的初始化，不是指指针的定义，而是指针变量存储的数值是个无效的数值。比如定义</SPAN><SPAN
lang=EN-US>float a;</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">这个</SPAN><SPAN
lang=EN-US>a</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">会分配一个地址，但初始值是一个乱七八糟的数据。同样，</SPAN><SPAN
lang=EN-US>float *a</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">；也会为</SPAN><SPAN
lang=EN-US>a</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">分配一个地址，初始值也是乱七八糟的数据。初始化可以将</SPAN><SPAN
lang=EN-US>a = NULL</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，这样在以后的程序中可以增加</SPAN><SPAN
lang=EN-US>if(a == NULL)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">来判断指针是否有效，否则不行。或者为指针分配或者指定空间。如</SPAN><SPAN
lang=EN-US> float *a = new float;</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或者</SPAN><SPAN
lang=EN-US>float b; float *a = &b</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">；都可以为指针指向一块内存以实现初始化。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">．指针越界</SPAN></FONT></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>指针越界是个比较难以捕捉的错误。如果测试不全面，不容易被发现。对于为指针分配的空间大小，程序员一定要时刻注意。</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">．指向局部变量的指针</SPAN></FONT></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'">指针是记录某块内存起始地址的变量，要使指针有效，则必须确保这块内存有效。用</SPAN><SPAN
lang=EN-US>new</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">分配的内存空间，只要不</SPAN><SPAN
lang=EN-US>delete</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，则一直有效。但是对于指向某个变量地址的指针，程序员必须清楚该变量的作用域。如果离开了变量的作用域，该变量的内存空间就会被系统自动回收，再使用指针时，将会发生错误。这是程序中最容易出现的错误。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><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'">．指针指向的转移</SPAN></FONT></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'">有些初涉</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'">的程序员，常常会写出这样的程序：</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>char *pChar = new char;</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>char chs;</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>pChar = &chs;</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21.75pt"><SPAN
lang=EN-US><FONT size=3>delete pChar;</FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 21.75pt"><FONT size=3><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">他们的目的是想将</SPAN><SPAN
lang=EN-US>chs</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">内容传递给</SPAN><SPAN
lang=EN-US>pChar</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指针指向的内存。但这样写，将会使</SPAN><SPAN
lang=EN-US>pChar</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">先前指向的空间编程垃圾地址，因为地址无法再获取了。俗称野指针。将会导致内存泄漏。而且，在调用</SPAN><SPAN
lang=EN-US>delete pChar</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时，也会发生异常错误。因为不是</SPAN><SPAN
lang=EN-US>new</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的空间是不能使用</SPAN><SPAN
lang=EN-US>delete</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">删除的。因为</SPAN><SPAN
lang=EN-US>pChar</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">已经转到指向</SPAN><SPAN
lang=EN-US>chs</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">这个变量的地址了。</SPAN></FONT></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'">指针的艺术远不止这些，留待我们的爱好者进行深入的探讨。指针给我们的程序带来了太多的方便，同样，它也有很多难以控制的问题。如何更好的驾驭指针，可以说是</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'">程序员提高自己的一个手段。</SPAN></FONT></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'">『注』本文参考了博客网的C++入门笔记，综合了笔者自己对指针的理解。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3> <o:p></o:p></FONT></SPAN></P>
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lang=EN-US><FONT size=3> <o:p></o:p></FONT></SPAN></P>
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lang=EN-US><FONT size=3> <o:p></o:p></FONT></SPAN></P>
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lang=EN-US><FONT size=3> <o:p></o:p></FONT></SPAN></P>
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lang=EN-US><FONT
size=3> <o:p></o:p></FONT></SPAN></P><BR></TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE><BR>
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