Windows API and DLLs --- Part-I

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Full form : API --- Application Programming
Interface

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DLL --- Dynamic Link Library

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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.

?áSo 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.

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

Any program you write has access to the Windows DLLs.

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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.

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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 :

?áHere are two examples :

Here is an example for calling a simple API routine:

This example sounds the speaker