DLL Basics

General 

• Bindings
  • Early binding
    • Loaded when program starts
  • Late binding
    • Loaded after program has started
    • Calls LoadLibrary() to load dll
    • Calls GetProcAddress() to get function address
    • Calls FreeLibrary() to to unload dll

Contents

• Functionis
• Resources
  • Bitmaps
  • Fonts
• Static global variables
• DLL interface
• DllMain() function

Varieties of DLL

• MFC extension DLL
• Regular DLL
  • Statically linked to MFC
  • Dynamically linked to MFC

Create DLL

• Export class
  • Append AFX_EXT_CLASS to the class specifier
    • class AFX_EXT_CLASS CMyClass {…}
  • Or use the .def file
    • #define DLLEXPORT _declspec(dllexport)
    • DLLEXPORT double avalue = 1.5;
    • DLLEXPORT CString FinWinner(CString* Teams);
• Add to StdAfx.h (StdAfx is acronym for standard application framework extenstion, later called MFC) 
  • #include <afxtempl.h>
• Build artifacts
  • MyDll.dll
    • Contains executable code
  • MyDll.lib
    • Contains definitions of item that are exported from DLL
    • Must be avaible to client application linker 

Files required to use DLL

• .h file
  • Defines items exported from dll
  • Need to be included in the host application 
    • #include “SimpleDll.h”
• .lib file
  • Used by linker to link host application to dll
  • Need to be included in the Project Link path
    • Project -> Settings -> Link
• .dll file
  • Contains executable code for the dll
  • Need to be in the system path with all its dependency dlls, e.g. Debug folder or System32 folder