📄 csdn_文档中心_c++中的内部连接与外部连接(一).htm
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style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">有两种声明不能重复，那就是类成员函数及静态数据成员的声明</SPAN></FONT></P>
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lang=EN-US><SPAN style="mso-tab-count: 1"><FONT
size=3>
</FONT></SPAN></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN><SPAN style="COLOR: green">class foo
<o:p></o:p></SPAN></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>{ <o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>static int i; <o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US style="COLOR: green"><SPAN
style="mso-tab-count: 1">
</SPAN>static int i;</SPAN><SPAN lang=EN-US
style="COLOR: red">//</SPAN><SPAN
style="COLOR: red; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">不可以</SPAN><SPAN
lang=EN-US style="COLOR: green"> <o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>public: <o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>int foo(); <o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US style="COLOR: green"><SPAN
style="mso-tab-count: 1">
</SPAN>int foo();</SPAN><SPAN lang=EN-US
style="COLOR: red">//</SPAN><SPAN
style="COLOR: red; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">不可以</SPAN><SPAN
lang=EN-US style="COLOR: green"> <o:p></o:p></SPAN></FONT></P>
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style="COLOR: green"><FONT size=3><SPAN
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</SPAN>};<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3> <o:p></o:p></FONT></SPAN></P>
<H2 style="MARGIN: 13pt 0cm"><SPAN lang=EN-US><FONT
face=Arial>2.</FONT></SPAN><SPAN
style="FONT-FAMILY: 黑体; mso-ascii-font-family: Arial">定义</SPAN></H2>
<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'">一个定义提供一个实体</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'">类型、实例、函数</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'">在一个作用域的唯一描述。</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'">在同一作用域中不可重复定义一个实体。</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'">以下都是定义。</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><SPAN style="COLOR: green">int
y;<o:p></o:p></SPAN></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>class foo {...};<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>struct bar {...};<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>foo* p;<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>static int i;<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>enum Color{RED,GREEN,BLUE};<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>const double PI = 3.1415;<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>union Rep{...};<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>void test(int p) {};<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>foo a;<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US
style="COLOR: green"><FONT size=3><SPAN
style="mso-tab-count: 1">
</SPAN>bar b;<o:p></o:p></FONT></SPAN></P>
<H2 style="MARGIN: 13pt 0cm"><SPAN lang=EN-US><FONT
face=Arial>3.</FONT></SPAN><SPAN
style="FONT-FAMILY: 黑体; mso-ascii-font-family: Arial">编译单元</SPAN></H2>
<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'">当一个</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'">或</SPAN><SPAN
lang=EN-US>cpp</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">文件在编译时，预处理器首先递归包含头文件，形成一个含有所有</SPAN><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'">必要信息的单个源文件</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'">这个源文件就是一个编译单元。这个编译单元会被编译成为一个与</SPAN><SPAN
lang=EN-US>cpp</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">文件名同名的目标文件</SPAN><SPAN
lang=EN-US>(.o</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或是</SPAN><SPAN
lang=EN-US>.obj)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。连接程序把不同编译单元中产生的符号联系起来，构成一个可执行程序。</SPAN></FONT></P>
<H2 style="MARGIN: 13pt 0cm"><SPAN lang=EN-US><FONT
face=Arial>4.</FONT></SPAN><SPAN
style="FONT-FAMILY: 黑体; mso-ascii-font-family: Arial">自由函数</SPAN></H2>
<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'">如果一个函数是自由函数，那么这个函数不是类的成员函数，也不是友元函数。</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>
<H3 style="MARGIN: 13pt 0cm"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=5>下面来看内部连接和外部连接</FONT></SPAN></H3>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US><SPAN
style="mso-tab-count: 1">
</SPAN></SPAN><B><I><SPAN
style="FONT-FAMILY: 宋体; FONT-SIZE: 12pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">内部连接</SPAN></I></B><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">：如果一个名称对于它的编译单元来说是局部的，并且在连接时不会与其它编译单元中的同样的名称相冲突，那么这个名称有内部连接</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'">注：有时也将声明看作是无连接的，这里我们统一看成是内部连接的</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'">。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><SPAN style="mso-tab-count: 1"><FONT
size=3>
</FONT></SPAN></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'">以下情况有内部连接</SPAN><SPAN
lang=EN-US>:</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>a)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所有的声明</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>b)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">名字空间</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'">包括全局名字空间</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'">中的静态自由函数、静态友元函数、静态变量的定义</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
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