📄 csdn_文档中心_vb与vc通信初探（二）.htm
字号:
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">
在通过</SPAN><SPAN lang=EN-US>DLL</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">实现</SPAN><SPAN
lang=EN-US>VB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">与</SPAN><SPAN
lang=EN-US>VC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的过程中，一般的简单的通信过程很容易建立。在《</SPAN><SPAN
lang=EN-US>VB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">与</SPAN><SPAN
lang=EN-US>VC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">通信初探（一）》中，我已经把基本的通信过程给描述了一下，但是，有些时候，事件的发展并不总是一帆风顺的，当我们以为可以轻松的实现</SPAN><SPAN
lang=EN-US>VB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">与</SPAN><SPAN
lang=EN-US>VC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的通信的时候，就经常发生这样的情况，还是先看看例子再说。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3> <?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office"
/><o:p></o:p></FONT></SPAN></P>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US>VC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中的程序：</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>extern "C" _declspec(dllexport)<SPAN
style="mso-spacerun: yes"> </SPAN>bool<SPAN
style="mso-spacerun: yes"> </SPAN>ReadString(LPCSTR
lpString)</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">
</SPAN>{</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><SPAN style="mso-spacerun: yes"> </SPAN>char
str[]="Hello World!"; </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><SPAN style="mso-spacerun: yes">
</SPAN>if(strcmp(lpString,str)==0)</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-tab-count: 2">
</SPAN>return true ;</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><SPAN style="mso-spacerun: yes">
</SPAN>else</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-tab-count: 2">
</SPAN>return false ;</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>}</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>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><SPAN
lang=EN-US>VB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中的程序：</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>Private Declare Function ReadString Lib
"commication.dll" (ByVal send As String) as
Boolean</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>……………………</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>Dim result As Boolean</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>Dim send As String</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>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>send =”Hello,World!”</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>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>result =
ReadString(send)</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>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>If result Then</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-spacerun: yes"> </SPAN>MsgBox "The return value is
'true'"</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>Else</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3><SPAN
style="mso-spacerun: yes"> </SPAN>MsgBox "The return value is
'false'"</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>End If</FONT></SPAN></P></BLOCKQUOTE>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3> <o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
lang=EN-US><FONT size=3>
</FONT></SPAN><FONT size=3><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">可以上机运行这个程序，一样的，实现了通信的功能，但是这里有几个地方是应该引起我们注意的，首先就是在</SPAN><SPAN
lang=EN-US>VB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中声明传递的字符串参数的时候，按照常规的理解，好像应该是传递地址才对，但是这里使用的方法是</SPAN><SPAN
lang=EN-US>ByVal</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，为什么？原因比较复杂，但是可以简单的来分析一下，在</SPAN><SPAN
lang=EN-US>VB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中，使用的字符串实际上是</SPAN><SPAN
lang=EN-US>BSTR</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">类型的，</SPAN><SPAN
class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">它是由自动化（以前被称为</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US style="FONT-FAMILY: Arial">OLE
Automation</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">）定义的数据类型。一个</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">BSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">由头部和字符串组成，头部包含了字符串的长度信息，字符串中可以包含嵌入的</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">null</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">值。大部分的</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">BSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">是</SPAN></SPAN><SPAN
class=txt><SPAN style="FONT-FAMILY: Arial"> <SPAN
lang=EN-US>Unicode</SPAN></SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">的，即每个字符需要两个字节。</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">BSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">通常以两字节的两个</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">null</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">字符结束。下图表示</SPAN></SPAN><SPAN
class=txt><SPAN style="FONT-FAMILY: Arial"> </SPAN></SPAN><SPAN
class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">了一个</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">BSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">类型的字符串。</SPAN></SPAN></FONT><SPAN
lang=EN-US style="FONT-FAMILY: Arial"><BR><BR></SPAN><FONT
size=3><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial"> （前缀）</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">aTest\0</SPAN></SPAN></FONT><SPAN
lang=EN-US style="FONT-FAMILY: Arial"><BR></SPAN><FONT size=3><SPAN
class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial"> 头部</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">BSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">指向数据的第一个字节</SPAN></SPAN></FONT><SPAN
lang=EN-US style="FONT-FAMILY: Arial"><BR><BR></SPAN><FONT
size=3><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial"> 另一方面，大部分的</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">DLL</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">过程（包括</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US style="FONT-FAMILY: Arial">Windows 95
API</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">中的所有过程）使用</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">LPSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">类型字符串，这是指向标准的以</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">null</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">结束的</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">C</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">语言字符串的指针，它也被称为</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">ASCIIZ</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">字符串。</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US style="FONT-FAMILY: Arial">LPSTR
</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">没有前缀。下图显示了一个指向</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">ASCIIZ</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">字符串的</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">LPSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">。</SPAN></SPAN></FONT><SPAN
lang=EN-US style="FONT-FAMILY: Arial"><BR><BR></SPAN><FONT
size=3><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial"> </SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">aTest\0</SPAN></SPAN></FONT><SPAN
lang=EN-US style="FONT-FAMILY: Arial"><BR><BR></SPAN><FONT
size=3><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial"> </SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">LPSTR</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">指向一个以</SPAN></SPAN><SPAN
class=txt><SPAN lang=EN-US
style="FONT-FAMILY: Arial">null</SPAN></SPAN><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">结尾的字符串数据的第一个字节</SPAN></SPAN></FONT><SPAN
lang=EN-US style="FONT-FAMILY: Arial"><BR><BR></SPAN><FONT
size=3><SPAN class=txt><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">
通过上面的简单分析，不难看出，如果均以地址的方式传递参数的话，那么</SPAN></SPAN><SPAN class=txt><SPAN
lang=EN-US style="FONT-FAMILY: Arial">VB</SPAN></SPAN><SPAN
class=txt><SPAN
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