Windows API and DLLs --- Part-I

Full form : API --- Application Programming
Interface

                  
DLL --- Dynamic Link Library

The Windows API is a collection of routines available to you,
the Visual Basic programmer. In a way, these API routines are like internal
functions of Visual Basic.

 So many Windows API routines exist that just about
anything you can do from Windows, you can do from a Visual Basic application by
calling the appropriate Windows API routine.

All Windows API routines are stored in files called DLLs.
Several thousand API routines are available for use.

Note : Most DLL files have '.DLL' extension.

Any program you write has access to the Windows DLLs.

Following are the three most common DLLs :

• 
  

  USER32.DLL --- Contains functions that control the
  Windows environment and the user's interface, such as cursors, menus,
  windows etc.



• 
  

  GDI32.DLL --- Contains functions that control output
  to the screen and other devices.



• 
  

  KERNEL32.DLL --- Contains functions that control the
  internal Windows hardware and software interface.

There are other DLLs such as COMDLG.DLL, MAPI32.DLL,
NETAPI32.DLL, WINMM.DLL etc.

Using the 'Declare'
statement

Calling Windows API routines requires a statement called
'Declare'.

The 'Declare' statement performs the following tasks :

• 
  

  Specifies where the API function is located



• 
  

  Identifies arguments needed by the API function by number
  and data type



• 
  

  Specifies whether or not the API function returns a value

The following format describes the subroutine procedure version
of the 'Declare' statement :

 Here are two examples :

Here is an example for calling a simple API routine:

This example sounds the speaker