My own written DLL not accessible in dialog based app; [modified]

[AmbiguousName]

hllo guys...I tried to write my own DLL with simple functions which so far im successful. It lookd like this

MyDll.h

namespace MyDll
{
class MyOwnDll
{
//function here
static _declspec(dllexport) void PrintMsg();
};
}

MyDll.cpp

namespace MyDll
{
void MyOwnDll::PrintMsg()
{
::MessageBox(0,"","",0);
}
}

Now I added this DLL to my dialog based application (MyDll.h in "stdafx.h" of MyProj) and build the solution. Everything is fine and it builds. But when I try to use this, it show errors stating Undeclared Identifier. Here is how I use it

MyProjDlg.cpp

{
...............
...............

 void MyProjDlg::MyMsg() //function added to a button
 {
     MyOwnDll mod;     //myTapi, mod ==> Undeclared Identifier
     mod.PrintMsg();  //mod ==> Undeclared Identifier
 }

}

All the paths and libraries are included, everything looks fine. But why it is not able to find this?? :confused: thnx

modified on Thursday, December 2, 2010 2:47 PM

[Aescleal]

You haven't qualified the class name with the namespace it's in, eg:

MyDll::MyOwnDll mod;

No idea if that's the source of your problem but it's a good place to start. Another thing to watch out for is the way you export the function from the DLL. Ideally you want to export the name in the DLL and import it in the EXE file. It might be worth having a look at some sample code to see how you're supposed to do that. Cheers, Ash

[Sauro Viti]

On your header file you have declared your export as __declspec(dllexport): this is right as it instruct the compiler that the method MyOwnDll::PrintMsg() is implemented in your code and should be exported from the library. On the other hand, when you use the dll, you should include the header file, but you need the MyOwnDll::PrintMsg() method to be imported, then it should be declared as __declspec(dllimport). A typical approach, is to add a pre-processor definition in your dll project, for example MYOWNDLLPRJ, and modify the header file as follow:

#ifdef MYOWNDLLPRJ
#define MYOWNDLLAPI __declspec(dllexport)
#else
#define MYOWNDLLAPI __declspec(dllimport)
#endif

namespace MyDll
{
class MyOwnDll
{
//function here
static MYOWNDLLAPI void PrintMsg();
};
}

[AmbiguousName]

Since im new to DLLs so plz dont mind. After this, how do I call this function in MyProjDlg.cpp? Like this?

void MyProjDlg::MyMsg()
{
MyDll::MyOwnDll mod;
mod.PrintMsg();
}

[Sauro Viti]

That will work, but is not the right way: as the MyDll::MyOwnDll.PrintMsg() method is static, you don't need to instantiate an object of your class to call it. The right way is the following:

void MyProjDlg::MyMsg()
{
MyDll::MyOwnDll::PrintMsg();
}