Basic API concept

[JaredM]

Can someone explain to me the basic concept of API and the parts of it and how it functions just be declaring an API call?

Also, how does one go about understanding and using advanced API?

[mlewis]

OK well the way Windows works is this:

You have a bunch of processes, which are launched by EXEs/DLLs/etc. Each process can have several threads. The threads are the things that do all the work.

Normally, for a program to do something, one of its threads has to have the instructions that make that something happen.

Now the way API works is that your program says, I don't want to store this code myself, because someone else already did it, and here's the code I want to run when I want to do this. That is the Declare statement.

A Declare statement is sort of like a link on a web page: activating it takes you somewhere else; for API, it tells Windows to run code from a thread that doesn't belong to your program.

ActiveX also uses the same idea, but it adds in COM and some other messy stuff that I won't go into here.

Windows API functions are categorized into 3 main parts:

GDI (graphics device interface, handles EVERYTHING you see on the screen)

USER (which is basically stuff for making your program work and making all programs work basically the same way, with taskbar buttons and so on)

and

KERNEL (which handles actually creating and managing processes and threads)

In addition to the 3 windows API sets, you can access API functions from other programs or DLLs.



Now about advanced API...what exactly do you mean there?

[jim mcnamara]

api is application programming interface.

Basically it is a large group (5400+) of functions provided by components of the OS and the browser. Many functions are not callable in VB or or not documented. VB'er's use about 700-800 of these calls. Probably maybe 5-15 per program.

To get help with api download the api-guide & apiviewer from www.allapi.net

www.allapi.net
www.vbapi.com
www.mvps.org/vbnet

are all excellent sources for sample code for using api calls.

[tamathaltarak]

Thanks - I have also been looking for API info and how to use.