DllImportAttribute problem with VC++.Net

Hi,
I'm using visual c++.net 2003 and I'm having a problem getting
DllImportAttribute to import a function from a .dll...

The error message that I'm receiving:

LIBCMTD.lib(wincrt0.obj) : error LNK2019: unresolved external symbol
_WinMain@16 referenced in function _WinMainCRTStartup
C:\DATA\Visual Studio Projects\eDNA Test Code\Debug\eDNA Test Code.exe :
fatal error LNK1120: 1 unresolved externals

Here is my code:

#include "stdafx.h"
#include "time.h"
#include <string>

#using <mscorlib.dll>

using namespace System;
using namespace System::Runtime::InteropServices;
using namespace System::IO;
using namespace std;
using namespace System::Collections;

[DllImportAttribute("ezdnaapi.dll", EntryPoint= "DNAGetRTValueAsString",
CharSet=CharSet::Auto)]
extern int DNAGetRTValueAsString(char *szPoint, char *szValue, unsigned
short nValue);


The dll is in the systems32 folder.
Can anyone give me some advice with this?
thanks!
Sande

William
Tue Apr 11 19:24:20 CDT 2006

"evilpixie" <evilpixie@discussions.microsoft.com> wrote in message
news:4535B31C-54CB-4FE2-BE4E-7AF2908065EB@microsoft.com...
> I'm using visual c++.net 2003 and I'm having a problem getting
> DllImportAttribute to import a function from a .dll...
>
> The error message that I'm receiving:
>
> LIBCMTD.lib(wincrt0.obj) : error LNK2019: unresolved external symbol
> _WinMain@16 referenced in function _WinMainCRTStartup
> C:\DATA\Visual Studio Projects\eDNA Test Code\Debug\eDNA Test Code.exe :
> fatal error LNK1120: 1 unresolved externals
>
> Here is my code:
>
> #include "stdafx.h"
> #include "time.h"
> #include <string>
>
> #using <mscorlib.dll>
>
> using namespace System;
> using namespace System::Runtime::InteropServices;
> using namespace System::IO;
> using namespace std;
> using namespace System::Collections;
>
> [DllImportAttribute("ezdnaapi.dll", EntryPoint= "DNAGetRTValueAsString",
> CharSet=CharSet::Auto)]
> extern int DNAGetRTValueAsString(char *szPoint, char *szValue, unsigned
> short nValue);
>
>
> The dll is in the systems32 folder.
> Can anyone give me some advice with this?

The error message is telling you that it can't find a proper entry point for
your application. What kind of application do you want to build? Did you
create the project from scratch or use the wizard?

Regards,
Will

evilpixie
Wed Apr 12 10:45:02 CDT 2006

I used the wizard. (Go to New->Project->select Console Application from
choices listed and then poof! Automagically I have a set of files.)

This code is eventually going to be in a Windows Service. I am
writing/testing it outside of the Service shell because I was told that it's
easier to debug that way. (I am new to VC++.Net) This advice came with the
advice to select the Console Application setup.

In the documentation for the .dll, it is listed as int WINAPI
DNAGetRTValueAsString(char *szPoint, char *szValue, unsigned short nValue)

If I list it as such in my code (with the windows.h header file) I get the
same error.

Thanks for your help, I really appreciate it!
Sande

"William DePalo [MVP VC++]" wrote:

> "evilpixie" <evilpixie@discussions.microsoft.com> wrote in message
> news:4535B31C-54CB-4FE2-BE4E-7AF2908065EB@microsoft.com...
> > I'm using visual c++.net 2003 and I'm having a problem getting
> > DllImportAttribute to import a function from a .dll...
> >
> > The error message that I'm receiving:
> >
> > LIBCMTD.lib(wincrt0.obj) : error LNK2019: unresolved external symbol
> > _WinMain@16 referenced in function _WinMainCRTStartup
> > C:\DATA\Visual Studio Projects\eDNA Test Code\Debug\eDNA Test Code.exe :
> > fatal error LNK1120: 1 unresolved externals
> >
> > Here is my code:
> >
> > #include "stdafx.h"
> > #include "time.h"
> > #include <string>
> >
> > #using <mscorlib.dll>
> >
> > using namespace System;
> > using namespace System::Runtime::InteropServices;
> > using namespace System::IO;
> > using namespace std;
> > using namespace System::Collections;
> >
> > [DllImportAttribute("ezdnaapi.dll", EntryPoint= "DNAGetRTValueAsString",
> > CharSet=CharSet::Auto)]
> > extern int DNAGetRTValueAsString(char *szPoint, char *szValue, unsigned
> > short nValue);
> >
> >
> > The dll is in the systems32 folder.
> > Can anyone give me some advice with this?
>
> The error message is telling you that it can't find a proper entry point for
> your application. What kind of application do you want to build? Did you
> create the project from scratch or use the wizard?
>
> Regards,
> Will
>
>
>

William
Wed Apr 12 10:52:26 CDT 2006

"evilpixie" <evilpixie@discussions.microsoft.com> wrote in message
news:9C317201-F56B-4DBD-98C9-3C6758190B42@microsoft.com...
>I used the wizard. (Go to New->Project->select Console Application from
> choices listed and then poof! Automagically I have a set of files.)
>
> This code is eventually going to be in a Windows Service. I am
> writing/testing it outside of the Service shell because I was told that
> it's
> easier to debug that way. (I am new to VC++.Net) This advice came with
> the
> advice to select the Console Application setup.
>
> In the documentation for the .dll, it is listed as int WINAPI
> DNAGetRTValueAsString(char *szPoint, char *szValue, unsigned short nValue)
>
> If I list it as such in my code (with the windows.h header file) I get the
> same error.

OK. Does your application begin executing user code at main() as windowed
applications start at WinMain()?

> Thanks for your help, I really appreciate it!

You are welcome.

Regards,
Will

evilpixie
Wed Apr 12 11:18:02 CDT 2006

It begins executing at int _tmain().

"William DePalo [MVP VC++]" wrote:

> "evilpixie" <evilpixie@discussions.microsoft.com> wrote in message
> news:9C317201-F56B-4DBD-98C9-3C6758190B42@microsoft.com...
> >I used the wizard. (Go to New->Project->select Console Application from
> > choices listed and then poof! Automagically I have a set of files.)
> >
> > This code is eventually going to be in a Windows Service. I am
> > writing/testing it outside of the Service shell because I was told that
> > it's
> > easier to debug that way. (I am new to VC++.Net) This advice came with
> > the
> > advice to select the Console Application setup.
> >
> > In the documentation for the .dll, it is listed as int WINAPI
> > DNAGetRTValueAsString(char *szPoint, char *szValue, unsigned short nValue)
> >
> > If I list it as such in my code (with the windows.h header file) I get the
> > same error.
>
> OK. Does your application begin executing user code at main() as windowed
> applications start at WinMain()?
>
> > Thanks for your help, I really appreciate it!
>
> You are welcome.
>
> Regards,
> Will
>
>
>

William
Wed Apr 12 12:03:00 CDT 2006

"evilpixie" <evilpixie@discussions.microsoft.com> wrote in message
news:D2C452FC-AC6B-4BD2-9D3C-4ECA24D81D85@microsoft.com...
> It begins executing at int _tmain().

Then that is your problem. The linker is telling you that it can't find
WinMain(). It is doing that presumably because you asked the wizard to
create something other than a "console application".

You have two choices:

1) You can go back and recreate a new "console application" project.

2) You can replace _tmain() with this

int WINAPI WinMain(
HINSTANCE hInstance, // handle to current instance
HINSTANCE hPrevInstance, // handle to previous instance
LPSTR lpCmdLine, // command line
int nCmdShow // show state
);

And if you need the tradional argc and argv variables they are available as

extern int _argc;
extern char **_argv;

The trouble with this approach is that you can not use the C standard I/O
(printf) or C++ output streams (std::cout) without extra work. Rather, you
are expected to use windows as display elements.

Regards,
Will







Regards,
Will