Thank you very much. It works now.

Somefunc is in the EXE.

///EXE code
class CDervDlg : public CDialog
{
void TestLoad();
void SomeFunc(CString, CString);

BOOL m\_SomeVar;

};

typedef int (*SCGptr)(CDervDlg *);
void TestLoad()
{
HINSTANCE inst = AfxLoadLibrary("testlib.dll");
SCGptr Startfunc = (SCGptr)GetProcAddress(inst, "?Start@@YAHPAVCDervDlg@@@Z");
if (Startfunc != NULL)
Startfunc(this);
}

///DLL code
#include "DervDlg.h"

__declspec(dllexport) int Start(CDervDlg *dlg)
{
dlg->m_SomeVar = TRUE; //Works fine
dlg->SomeFunc("Blah", "Blah"); //Link error: unresolved external symbol.
}

Thank you for helping.

I have been having problems trying to set up a plugin for my program. The program loads a DLL dynamically, and then calls a member function:

__declspec(dllexport) int Start(CDervDlg *dlg)
{
dlg->m_SomeVar = TRUE; //Works fine
dlg->SomeFunc("Blah", "Blah"); //Link error: unresolved external symbol.
}

I've tried using both regular DLLs and Extension DLLs, but neither work. This is probably just something obvious that I just can't see, but can anyone help?