What is DLL?

A dynamic-link library (DLL) is a module that contains functions and data that can be used by another module (application or DLL).

A DLL can define two kinds of functions: exported and internal. The exported functions are intended to be called by other modules, as well as from within the DLL where they are defined. Internal functions are typically intended to be called only from within the DLL where they are defined. Although a DLL can export data, its data is generally used only by its functions. However, there is nothing to prevent another module from reading or writing that address.

DLLs provide a way to modularize applications so that their functionality can be updated and reused more easily. DLLs also help reduce memory overhead when several applications use the same functionality at the same time, because although each application receives its own copy of the DLL data, the applications share the DLL code.

Types of Dynamic Linking

There are two methods for calling a function in a DLL:

• In load-time dynamic linking, a module makes explicit calls to exported DLL functions as if they were local functions. This requires you to link the module with the import library for the DLL that contains the functions. An import library supplies the system with the information needed to load the DLL and locate the exported DLL functions when the application is loaded.

• In run-time dynamic linking, a module uses the LoadLibrary or LoadLibraryEx function to load the DLL at run time. After the DLL is loaded, the module calls the GetProcAddress function to get the addresses of the exported DLL functions. The module calls the exported DLL functions using the function pointers returned by GetProcAddress. This eliminates the need for an import library.

Check out the Project Source Code for more detailed info on implementation.