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详细讲解动态链接库的文档,在VIsual c++开发环境下使用,适合新手学习

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      <UL class=download>
        <LI><A 
        href="http://www.codeproject.com/KB/DLL/Dllfun/SourceCode.zip">Download 
        source code - 21.8 kb</A> 
        <LI><A 
        href="http://www.codeproject.com/KB/DLL/Dllfun/DemoProject.zip">Download 
        demo project - 10.5 kb</A></LI></UL>
      <P><IMG height=257 alt="Sample screenshot" src="111.files/Image1.gif" 
      width=306></P>
      <H2>Introduction</H2>
      <P>Some programmers think DLLs are complicated but it's true they are like 
      EXEs. However I have seen programmers who can't build DLL. There are 
      multiple way to create a DLL. For usage with exe, easiest way is "Implicit 
      linking". In this way, we require <I>.LIB</I> file produced by DevStudio. 
      Below, we create a DLL and then use it with exe. Inside DLL, we calculate 
      (multiply) two numbers that has been send from the exe. Practically, exe 
      is "Sender/Receiver" and DLL is "Calculator".</P>
      <H2>How to build MFC DLL?</H2>
      <OL>
        <LI>Run VC++. 
        <LI>Choose : File &gt; New. 
        <LI>Create "MFC AppWizard (DLL)" (named e.g. : MyFirstDll). 
        <LI>Declare in top of file: <PRE><SPAN class=code-comment>//</SPAN><SPAN class=code-comment>
</SPAN><SPAN class=code-preprocessor>#define</SPAN> DLLEXPORT <SPAN class=code-keyword>__declspec</SPAN>(<SPAN class=code-keyword>dllexport</SPAN>)
<SPAN class=code-comment>//</SPAN><SPAN class=code-comment>
</SPAN></PRE>
        <P><CODE><SPAN class=code-keyword>__declspec</SPAN>(<SPAN 
        class=code-keyword>dllexport</SPAN>)</CODE>'s purpose is to add the " 
        export directive " to the object file. So you don't need a <I>.DEF</I> 
        file. To make code more readable, define a macro for <CODE><SPAN 
        class=code-keyword>__declspec</SPAN>(<SPAN 
        class=code-keyword>dllexport</SPAN>) : DLLEXPORT</CODE>.</P>
        <LI>Now for exporting per function that you want, type before it : 
        "<CODE>DLLEXPORT</CODE>" like this: <PRE>DLLEXPORT <SPAN class=code-keyword>int</SPAN> Multiply(<SPAN class=code-keyword>int</SPAN> ParOne,<SPAN class=code-keyword>int</SPAN> ParTwo) 
{ 
   <SPAN class=code-keyword>int</SPAN> Mlt=ParOne*ParTwo; 
   <SPAN class=code-keyword>return</SPAN> Mlt; 
} </PRE>
        <LI>Press Build button. 
        <LI>Bring out DLL from oven!! 
        <P>Note that linker also builds an " import library " with the same DLL 
        name but with <I>.lib</I> extension.</P></LI></OL>
      <H2>How to use MFC DLL?</H2>
      <OL>
        <LI>Run VC++. 
        <LI>Choose : File &gt; New. 
        <LI>Create "MFC AppWizard (exe)". 
        <LI>Choose "Dialog based". 
        <LI>Choose : Project &gt; Add To Project &gt; New &gt; C/C++ Header 
        File. 
        <LI>Name file e.g. : Imports. 
        <LI>Declare in <I>Imports.h</I>: <PRE><SPAN class=code-comment>//</SPAN><SPAN class=code-comment>
</SPAN><SPAN class=code-preprocessor>#define</SPAN> DLLIMPORT <SPAN class=code-keyword>__declspec</SPAN>(<SPAN class=code-keyword>dllimport</SPAN>) 
<SPAN class=code-comment>//</SPAN><SPAN class=code-comment></SPAN></PRE>
        <P><CODE><SPAN class=code-keyword>__declspec</SPAN>(<SPAN 
        class=code-keyword>dllimport</SPAN>)</CODE>'s purpose is to add the " 
        import directive " to the object file. To make code more readable, 
        define a macro for <CODE><SPAN 
        class=code-keyword>__declspec</SPAN>(<SPAN 
        class=code-keyword>dllimport</SPAN>) : DLLIMPORT</CODE>.</P>
        <LI>Type after it: <PRE>DLLIMPORT <SPAN class=code-keyword>int</SPAN> Multiply(<SPAN class=code-keyword>int</SPAN> ParOne,<SPAN class=code-keyword>int</SPAN> ParTwo);</PRE>
        <P>This is the same function that you defined in DLL. Here, it has been 
        introduced as an "import function". But it is unrecognized for current 
        project and we must resolve it for linker.</P>
        <LI>Copy <I>.lib</I> file from release or debug folder (depends current 
        project setting) in previous project to current directory project 
        because it must link with exe. Inside <I>.lib</I> file (same import 
        library), exists information about exported functions of DLL. 
        <LI>Back to VC++ environment and Choose : Project &gt; Settings &gt; 
        Link (tab). 
        <LI>Type [<I>.lib</I> file previous project] in "Object/library 
        modules:". For example, <I>MyFirstDll.lib.</I> Then press OK. It will 
        resolve externals. Here, "<CODE><SPAN class=code-keyword>int</SPAN> 
        Multiply(<SPAN class=code-keyword>int</SPAN> ParOne,<SPAN 
        class=code-keyword>int</SPAN> ParTwo);</CODE>" function. 
        <LI>Because we intend to use function in <I>...Dlg.cpp</I> file (e.g.<I> 
        SimpleDllDlg.cpp</I>), type in top of file: <PRE><SPAN class=code-comment>//</SPAN><SPAN class=code-comment>