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API
(Advanced Programers Interface) is a set of predefined Windows functions
used to control the appearance and behavior of every Windows element (from
the outlook of the desktop window to the allocation of memory for a new
process). Every user action causes the execution of several or more API
function telling Windows what's happened.
It is something
like the native code of Windows. Other languages just act as a shell to
provide an automated and easier way to access APIs. VB has done a lot in
this direction. It has completely hidden the APIs and provided a quite
different approach for programming under Windows.
Here is the
place to say that, every line of code you write in VB is being translated
by VB into API function and sent to Windows. Thus calling something like
Form1.Print ... causes VB to call TextOut
API function with the needed parameters (either given by you in the code,
or taken by some defaults).
Also, when the
user click a button on your form, Windows sends a message to your windows
procedure (that is eventually hidden for you), VB gets the call, analyses
it and raises a given event (Button_Click)
for you.
The API functions
reside in DLLs (like User32.dll, GDI32.dll, Shell32.dll, ...) in the Windows
system directory. |
