[KLUG Members] API

[Eric Beversluis]

On Thu, 2005-02-10 at 07:24 -0500, Adam Tauno Williams wrote:
> > I often see references to 'API' (application-program interface), but
> > have never really seen a good definition of it. In fact, the term seems
> > to me to be used differently in different contexts. (An application IS a
> > program, so what exactly is being interfaced?) Could someone explain
> > exactly what API means in the following quotation (from CodeWeavers'
> > mission statement):
> 
> The "A" in API is the 'other-way-around'.  It isn't an interface TO an
> application (usually) it is an interface FOR an application to access services
> below it.
> 
> >      "re-implementing the Win32 API under Linux"
> 
> When you create a traditional (non-.NET, non-Macro, non-Java) application for
> Windows you are creating a Win32 application, that is - one that is comprised
> of a series of calls to routines provided by 32-bit Windows for applications to
> use, like: Draw Window, Put A Button Here,  Register Click Of Button To Call My
> Function X, Open The File "C:\Windows\Crash".
> 
> The 'below' in "access services below it" can be rather amourphous.  For
> instance there is an OpenOffice API, so you can build programs that invoke
> methods from Open Office to perform some task - in this sense OO is 'below'
> that application in the API stack.
> 
> In Linux -
> Glibc is the core library that provides an API (does it have a name?) to the
> POSIX-ish semantic of the Linux OS.  glib sits on top of glibc and adds some
> nicities and hides some of the variation between UNIX platforms.  libX11 sits
> on top of Glibc (and glib?) and provides primitive functions for 'put this
> bitmap at X,Y' and some basic window management functions.  GTK sits on top of
> libX11 and glib and provides the routines to 'associate this button with this
> function', 'make a scrollable window at X,Y' and paints the widgets you
> actually see in GNOME.  libgnome (and brethereb) sits on top of Gtk and
> provides the basic GNOME libraries allowing cut-n-paste, routines so an
> application can draw to a virtual page (make circle with diameter X at A in and
> B in from corner of page) and send it to a printer, etc...  There are LOTS of
> APIs in Linux (actually it is a bit of a problem).
> 
> Windows is a monolithic thing so you get one API: Win32  (well, not really true
> now, you also have .NET).

Very helpful. Thanks.
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