|
|
<p> </p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt" lang="EN-US">C++</span><span style="FONT-SIZE: 10.5pt">的<span lang="EN-US">static</span>有两种用法：面向过程程序设计中的<span lang="EN-US">static</span>和面向对象程序设计中的<span lang="EN-US">static</span>。前者应用于普通变量和函数，不涉及类；后者主要说明<span lang="EN-US">static</span>在类中的作用。 <span lang="EN-US"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com fficeffice" /><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 一、面向过程设计中的<span lang="EN-US">static<o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> <span lang="EN-US">1</span>、静态全局变量<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 在全局变量前，加上关键字<span lang="EN-US">static</span>，该变量就被定义成为一个静态全局变量。我们先举一个静态全局变量的例子，如下：<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all" class="MsoNormal"><code><span lang="EN-US">//Example 1</span></code><span lang="EN-US"><br/><code>#include <iostream.h></code><br/><code>void fn();</code><br/><code>static int n; //</code></span><code>定义静态全局变量</code><span lang="EN-US"><br/><code>void main()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> n=20;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<n<<endl;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> fn();</span></code><span lang="EN-US"><br/><code>}</code><br/><code>void fn()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> n++;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<n<<endl;</span></code><span lang="EN-US"><br/><code>}</code></span><span style="FONT-SIZE: 10.5pt">静态全局变量有以下特点： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">该变量在全局数据区分配内存； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">未经初始化的静态全局变量会被程序自动初始化为<span lang="EN-US">0</span>（自动变量的值是随机的，除非它被显式初始化）； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态全局变量在声明它的整个文件都是可见的，而在文件之外是不可见的； 静态变量都在全局数据区分配内存，包括后面将要提到的静态局部变量。对于一个完整的程序，在内存中的分布情况如下图： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> <span lang="EN-US"><o:p></o:p></span></span></p>
<p>
<table style="mso-cellspacing: 1.5pt" class="MsoNormalTable" border="1" cellpadding="0">
<tbody>
<tr style="mso-yfti-irow: 0; mso-yfti-firstrow: yes">
<td style="PADDING-BOTTOM: 0.75pt; PADDING-LEFT: 0.75pt; PADDING-RIGHT: 0.75pt; PADDING-TOP: 0.75pt">
<p class="MsoNormal"><span style="FONT-SIZE: 9pt">代码区<span lang="EN-US"><o:p></o:p></span></span></p></td></tr>
<tr style="mso-yfti-irow: 1">
<td style="PADDING-BOTTOM: 0.75pt; PADDING-LEFT: 0.75pt; PADDING-RIGHT: 0.75pt; PADDING-TOP: 0.75pt">
<p class="MsoNormal"><span style="FONT-SIZE: 9pt">全局数据区<span lang="EN-US"><o:p></o:p></span></span></p></td></tr>
<tr style="mso-yfti-irow: 2">
<td style="PADDING-BOTTOM: 0.75pt; PADDING-LEFT: 0.75pt; PADDING-RIGHT: 0.75pt; PADDING-TOP: 0.75pt">
<p class="MsoNormal"><span style="FONT-SIZE: 9pt">堆区<span lang="EN-US"><o:p></o:p></span></span></p></td></tr>
<tr style="mso-yfti-irow: 3; mso-yfti-lastrow: yes">
<td style="PADDING-BOTTOM: 0.75pt; PADDING-LEFT: 0.75pt; PADDING-RIGHT: 0.75pt; PADDING-TOP: 0.75pt">
<p class="MsoNormal"><span style="FONT-SIZE: 9pt">栈区<span lang="EN-US"><o:p></o:p></span></span></p></td></tr></tbody></table></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 一般程序的由<span lang="EN-US">new</span>产生的动态数据存放在堆区，函数内部的自动变量存放在栈区。自动变量一般会随着函数的退出而释放空间，静态数据（即使是函数内部的静态局部变量）也存放在全局数据区。全局数据区的数据并不会因为函数的退出而释放空间。细心的读者可能会发现，<span lang="EN-US">Example 1</span>中的代码中将<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class="MsoNormal"><code> <span lang="EN-US">static int n; //</span>定义静态全局变量</code><span style="FONT-SIZE: 10.5pt">改为</span><code> <span lang="EN-US">int n; //</span>定义全局变量</code><span style="FONT-SIZE: 10.5pt">程序照样正常运行。 <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 的确，定义全局变量就可以实现变量在文件中的共享，但定义静态全局变量还有以下好处： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态全局变量不能被其它文件所用； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">其它文件中可以定义相同名字的变量，不会发生冲突； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 您可以将上述示例代码改为如下：<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class="MsoNormal"><code><span lang="EN-US">//Example 2</span></code><span lang="EN-US"><br/><code>//File1</code><br/><code>#include <iostream.h></code><br/><code>void fn();</code><br/><code>static int n; //</code></span><code>定义静态全局变量</code><span lang="EN-US"><br/><code>void main()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> n=20;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<n<<endl;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> fn();</span></code><span lang="EN-US"><br/><code>}</code><br/><code>//File2</code><br/><code>#include <iostream.h></code><br/><code>extern int n;</code><br/><code>void fn()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> n++;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<n<<endl;</span></code><span lang="EN-US"><br/><code>}</code></span><span style="FONT-SIZE: 10.5pt">编译并运行<span lang="EN-US">Example 2</span>，您就会发现上述代码可以分别通过编译，但运行时出现错误。试着将</span><code><span lang="EN-US">static int n; //</span>定义静态全局变量</code><span style="FONT-SIZE: 10.5pt">改为</span><code><span lang="EN-US">int n; //</span>定义全局变量</code><span style="FONT-SIZE: 10.5pt">再次编译运行程序，细心体会全局变量和静态全局变量的区别。 <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> <span lang="EN-US">2</span>、静态局部变量<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 在局部变量前，加上关键字<span lang="EN-US">static</span>，该变量就被定义成为一个静态局部变量。<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 我们先举一个静态局部变量的例子，如下：<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class="MsoNormal"><code><span lang="EN-US">//Example 3</span></code><span lang="EN-US"><br/><code>#include <iostream.h></code><br/><code>void fn();</code><br/><code>void main()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> fn();</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> fn();</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> fn();</span></code><span lang="EN-US"><br/><code>}</code><br/><code>void fn()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> static n=10;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<n<<endl;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> n++;</span></code><span lang="EN-US"><br/><code>}</code></span><span style="FONT-SIZE: 10.5pt"> 通常，在函数体内定义了一个变量，每当程序运行到该语句时都会给该局部变量分配栈内存。但随着程序退出函数体，系统就会收回栈内存，局部变量也相应失效。 <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 但有时候我们需要在两次调用之间对变量的值进行保存。通常的想法是定义一个全局变量来实现。但这样一来，变量已经不再属于函数本身了，不再仅受函数的控制，给程序的维护带来不便。<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 静态局部变量正好可以解决这个问题。静态局部变量保存在全局数据区，而不是保存在栈中，每次的值保持到下一次调用，直到下次赋新值。 <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 静态局部变量有以下特点：<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">该变量在全局数据区分配内存； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态局部变量在程序执行到该对象的声明处时被首次初始化，即以后的函数调用不再进行初始化； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态局部变量一般在声明处初始化，如果没有显式初始化，会被程序自动初始化为<span lang="EN-US">0</span>； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">它始终驻留在全局数据区，直到程序运行结束。但其作用域为局部作用域，当定义它的函数或语句块结束时，其作用域随之结束； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> <span lang="EN-US">3</span>、静态函数<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 在函数的返回类型前加上<span lang="EN-US">static</span>关键字<span lang="EN-US">,</span>函数即被定义为静态函数。静态函数与普通函数不同，它只能在声明它的文件当中可见，不能被其它文件使用。<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 静态函数的例子：<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class="MsoNormal"><code><span lang="EN-US">//Example 4</span></code><span lang="EN-US"><br/><code>#include <iostream.h></code><br/><code>static void fn();//</code></span><code>声明静态函数</code><span lang="EN-US"><br/><code>void main()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> fn();</span></code><span lang="EN-US"><br/><code>}</code><br/><code>void fn()//</code></span><code>定义静态函数</code><span lang="EN-US"><br/><code>{</code><br/></span><code> <span lang="EN-US"> int n=10;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<n<<endl;</span></code><span lang="EN-US"><br/><code>}</code></span><span style="FONT-SIZE: 10.5pt">定义静态函数的好处： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态函数不能被其它文件所用； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">其它文件中可以定义相同名字的函数，不会发生冲突； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 二、面向对象的<span lang="EN-US">static</span>关键字（类中的<span lang="EN-US">static</span>关键字）<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> <span lang="EN-US">1</span>、静态数据成员<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 在类内数据成员的声明前加上关键字<span lang="EN-US">static</span>，该数据成员就是类内的静态数据成员。先举一个静态数据成员的例子。<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class="MsoNormal"><code><span lang="EN-US">//Example 5</span></code><span lang="EN-US"><br/><code>#include <iostream.h></code><br/><code>class Myclass</code><br/><code>{</code><br/><code>public:</code><br/></span><code> <span lang="EN-US"> Myclass(int a,int b,int c);</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> void GetSum();</span></code><span lang="EN-US"><br/><code>private:</code><br/></span><code> <span lang="EN-US"> int a,b,c;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> static int Sum;//</span>声明静态数据成员</code><span lang="EN-US"><br/><code>};</code><br/><code>int Myclass::Sum=0;//</code></span><code>定义并初始化静态数据成员</code><span lang="EN-US"><br/><code>Myclass::Myclass(int a,int b,int c)</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> this->a=a;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> this->b=b;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> this->c=c;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> Sum+=a+b+c;</span></code><span lang="EN-US"><br/><code>}</code><br/><code>void Myclass::GetSum()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> cout<<"Sum="<<Sum<<endl;</span></code><span lang="EN-US"><br/><code>}</code><br/><code>void main()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> Myclass M(1,2,3);</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US">M.GetSum();</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> Myclass N(4,5,6);</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> N.GetSum();</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> M.GetSum();</span></code><span lang="EN-US"><br/><code>}</code></span><span style="FONT-SIZE: 10.5pt">可以看出，静态数据成员有以下特点： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">对于非静态数据成员，每个类对象都有自己的拷贝。而静态数据成员被当作是类的成员。无论这个类的对象被定义了多少个，静态数据成员在程序中也只有一份拷贝，由该类型的所有对象共享访问。也就是说，静态数据成员是该类的所有对象所共有的。对该类的多个对象来说，静态数据成员只分配一次内存，供所有对象共用。所以，静态数据成员的值对每个对象都是一样的，它的值可以更新； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态数据成员存储在全局数据区。静态数据成员定义时要分配空间，所以不能在类声明中定义。在<span lang="EN-US">Example 5</span>中，语句<span lang="EN-US">int Myclass::Sum=0;</span>是定义静态数据成员； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态数据成员和普通数据成员一样遵从<span lang="EN-US">public,protected,private</span>访问规则； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">因为静态数据成员在全局数据区分配内存，属于本类的所有对象共享，所以，它不属于特定的类对象，在没有产生类对象时其作用域就可见，即在没有产生类的实例时，我们就可以操作它； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态数据成员初始化与一般数据成员初始化不同。静态数据成员初始化的格式为： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> ＜数据类型＞＜类名＞<span lang="EN-US">::</span>＜静态数据成员名＞<span lang="EN-US">=</span>＜值＞ <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">类的静态数据成员有两种访问形式： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> ＜类对象名＞<span lang="EN-US">.</span>＜静态数据成员名＞ 或 ＜类类型名＞<span lang="EN-US">::</span>＜静态数据成员名＞<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 如果静态数据成员的访问权限允许的话（即<span lang="EN-US">public</span>的成员），可在程序中，按上述格式来引用静态数据成员 ； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态数据成员主要用在各个对象都有相同的某项属性的时候。比如对于一个存款类，每个实例的利息都是相同的。所以，应该把利息设为存款类的静态数据成员。这有两个好处，第一，不管定义多少个存款类对象，利息数据成员都共享分配在全局数据区的内存，所以节省存储空间。第二，一旦利息需要改变时，只要改变一次，则所有存款类对象的利息全改变过来了； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">同全局变量相比，使用静态数据成员有两个优势： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态数据成员没有进入程序的全局名字空间，因此不存在与程序中其它全局名字冲突的可能性； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">可以实现信息隐藏。静态数据成员可以是<span lang="EN-US">private</span>成员，而全局变量不能； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> <span lang="EN-US">2</span>、静态成员函数 <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> 与静态数据成员一样，我们也可以创建一个静态成员函数，它为类的全部服务而不是为某一个类的具体对象服务。静态成员函数与静态数据成员一样，都是类的内部实现，属于类定义的一部分。普通的成员函数一般都隐含了一个<span lang="EN-US">this</span>指针，<span lang="EN-US">this</span>指针指向类的对象本身，因为普通成员函数总是具体的属于某个类的具体对象的。通常情况下，<span lang="EN-US">this</span>是缺省的。如函数<span lang="EN-US">fn()</span>实际上是<span lang="EN-US">this->fn()</span>。但是与普通函数相比，静态成员函数由于不是与任何的对象相联系，因此它不具有<span lang="EN-US">this</span>指针。从这个意义上讲，它无法访问属于类对象的非静态数据成员，也无法访问非静态成员函数，它只能调用其余的静态成员函数。下面举个静态成员函数的例子。<span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class="MsoNormal"><code><span lang="EN-US">//Example 6</span></code><span lang="EN-US"><br/><code>#include <iostream.h></code><br/><code>class Myclass</code><br/><code>{</code><br/><code>public:</code><br/></span><code> <span lang="EN-US"> Myclass(int a,int b,int c);</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> static void GetSum();/</span>声明静态成员函数</code><span lang="EN-US"><br/><code>private:</code><br/></span><code> <span lang="EN-US"> int a,b,c;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> static int Sum;//</span>声明静态数据成员</code><span lang="EN-US"><br/><code>};</code><br/><code>int Myclass::Sum=0;//</code></span><code>定义并初始化静态数据成员</code><span lang="EN-US"><br/><code>Myclass::Myclass(int a,int b,int c)</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> this->a=a;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> this->b=b;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> this->c=c;</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> Sum+=a+b+c; //</span>非静态成员函数可以访问静态数据成员</code><span lang="EN-US"><br/><code>}</code><br/><code>void Myclass::GetSum() //</code></span><code>静态成员函数的实现</code><span lang="EN-US"><br/><code>{</code><br/><code>//</code></span><code> <span lang="EN-US">cout<<a<<endl; //</span>错误代码，<span lang="EN-US">a</span>是非静态数据成员</code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> cout<<"Sum="<<Sum<<endl;</span></code><span lang="EN-US"><br/><code>}</code><br/><code>void main()</code><br/><code>{</code><br/></span><code> <span lang="EN-US"> Myclass M(1,2,3);</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> M.GetSum();</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> Myclass N(4,5,6);</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> N.GetSum();</span></code><span lang="EN-US"><br/></span><code> <span lang="EN-US"> Myclass::GetSum();</span></code><span lang="EN-US"><br/><code>}</code></span><span style="FONT-SIZE: 10.5pt">关于静态成员函数，可以总结为以下几点： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">出现在类体外的函数定义不能指定关键字<span lang="EN-US">static</span>； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态成员之间可以相互访问，包括静态成员函数访问静态数据成员和访问静态成员函数； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">非静态成员函数可以任意地访问静态成员函数和静态数据成员； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">静态成员函数不能访问非静态成员函数和非静态数据成员； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">由于没有<span lang="EN-US">this</span>指针的额外开销，因此静态成员函数与类的全局函数相比速度上会有少许的增长； <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="TEXT-INDENT: -18pt; MARGIN-LEFT: 0cm; WORD-BREAK: break-all; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l0="l0" level1="level1" lfo1; tab-stops: list="list" 36.0pt" class="MsoNormal"><span style="FONT-FAMILY: Symbol; FONT-SIZE: 10pt; mso-bidi-font-family: Symbol; mso-bidi-font-size: 10.5pt; mso-fareast-font-family: Symbol" lang="EN-US"><span style="mso-list: Ignore">·<span style="FONT: 7pt="7pt" 'Times New="New" Roman'"> </span></span></span><span style="FONT-SIZE: 10.5pt">调用静态成员函数，可以用成员访问操作符<span lang="EN-US">(.)</span>和<span lang="EN-US">(->)</span>为一个类的对象或指向类对象的指针调用静态成员函数，也可以直接使用如下格式： <span lang="EN-US"><o:p></o:p></span></span></p>
<p style="WORD-BREAK: break-all"><span style="FONT-SIZE: 10.5pt"> ＜类名＞<span lang="EN-US">::</span>＜静态成员函数名＞（＜参数表＞）<span lang="EN-US"><o:p></o:p></span></span></p>
<p><span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-bidi-font-family: 宋体; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA"> 调用类的静态成员函数</span></p> |
|
发表于 2009-5-23 10:25:42