Article #22432: How do I rename the "DllEntryPoint" function to "DllMain," which is the convention in some other compilers?

Question:

I would like to rename the DllEntryPoint function to DllMain, but the VCL produces an error message every time I try.  Is this possible?

Answer:

Normally, there is no need to change the name of this function, however, if you are attempting to use a DLL which uses a different naming convention for the DLL entry point function, you can use a .DEF file to export the desired name instead of the default.  For example, in C++Builder, the name of the function is  "DllEntryPoint," but in older Borland compilers (and VC) , the name of this function is "DllMain."

The VCL requires this function to be named as such (& will prevent you from saving/closing your application), but you can workaround this by adding "#define DllEntryPoint" (shown below), which merely adds the name to the symbol table.  So, an example of a DLL.CPP file using "DllMain" as the naming convention instead of "DllEntryPoint" might look like the following:

    //---------------------------------------------------------------------------
    // Just EXPORTS DllMain=DllEntryPoint
    USEDEF("MyDll.def");
    #define DllEntryPoint
    //---------------------------------------------------------------------------
    int WINAPI DllMain(HINSTANCE hinst, unsigned long reason, void*)
    {
            MessageBox(0,"OK?", "It Works",0);
            return 1;
    }
    //---------------------------------------------------------------------------
    // To prove to yourself that the DllMain is being exported correctly,
    // go to a command prompt, navigate to where your project is,
    // and type the following:
    //      tdump -ee MyDll.dll
    //---------------------------------------------------------------------------
 

Now, it is necessary to create the .DEF file.   Here is an example of what it should look like:

    //---------------------------------------------------------------------------
    LIBRARY  MYDLL.DLL

    EXPORTS
        DllMain=DllEntryPoint
    //---------------------------------------------------------------------------
 

That's basically it.  If you wish to see it in action, I have provided source code below that uses the DLL.  Just drop a button on your form and copy the following into the Unit.cpp of your application:
 

    //---------------------------------------------------------------------------
    #include <vcl.h>
    #pragma hdrstop
    #include "MainUnit.h"
    #pragma package(smart_init)
    #pragma resource "*.dfm"
    TForm1 *Form1;

    __fastcall TForm1::TForm1(TComponent* Owner)  : TForm(Owner)
    {
    }

    void __fastcall TForm1::Button1Click(TObject *Sender)
    {
            HINSTANCE h = LoadLibrary("MyDll.dll");
            FreeLibrary("MyDll.dll");
    }
    //---------------------------------------------------------------------------
 

Last Modified: 07-JUL-00