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Making a .DLL

Posted on 1999-11-15
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Last Modified: 2010-04-16
I have a lot of experience programming in Visual Basic, however I would like to take dozens of functions that I have written in VB and make them into a C++ dll.  Now, I am just learning C++ and don't know the slightest bit about what I am doing.  If anyone could point me to a sample project with several different types of functions and return values, either on the web or email it to me (header@rocketmail.com) that would be great.

If I can see a sample, I should be able to modify it to fit my needs.
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Question by:header
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chensu earned 100 total points
ID: 2210082
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by:header
ID: 2212389
I have taken the supplied demo from the msdn and added a function called 'Test'.


Here is my Select.def:

LIBRARY   Select

EXPORTS
    StartSelection      @2
    UpdateSelection     @3
    EndSelection        @4
    ClearSelection      @5
    Test              @6


Here is my Select.h:

....
int APIENTRY StartSelection(HWND, MPOINT, LPRECT, int);
int APIENTRY UpdateSelection(HWND, MPOINT, LPRECT, int);
int APIENTRY EndSelection(MPOINT, LPRECT);
int APIENTRY ClearSelection(HWND, LPRECT, int);
int APIENTRY Test(long);


and here is Select.c

....
INT APIENTRY Test(
    long message)
{
      return message;
}

When I call this function from visual basic, it always returns -2328.  I'm not sure what I am doing wrong to make it return the wrong value.  It seems as though the value I pass to it from VB is not getting there, possibly from a wrong declaration somewhere?

Also, I put this line at the top of Select.c:
#include <iostream.h>

I tried to use this line in the Test function:
cout << "Hello World";

However, when I compiled it said 'cout' was an undeclared identifier.  What am I doing wrong there?
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by:chensu
ID: 2212575
>When I call this function from visual basic, it always returns -2328.

I don't use Visual Basic. You need to find out what the error code means.

>However, when I compiled it said 'cout' was an undeclared identifier.  What am I doing wrong there?

Your source file is in C language (.c). But cout is C++ stuff. Use printf instead.
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by:header
ID: 2215081
I don't think I am getting an error message back.  If I say, for example:

return 12345;

VB returns the correct number (12345), the problem occurs when I change it to:

return message;

message is the parameter that was passed to the function, so I am wondering if there is something I did wrong to make the parameter not get passed or interpreted correctly.
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Expert Comment

by:chensu
ID: 2218491
So, what did you get?
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