Cheat Engine

[kitesan]

what does it mean to hook game's api?
how do i learn it?

[Gniarf]

An API (Application Programming Interface) is a function that a .dll or .exe publishes so that other dlls/exes can use it. When a function is "published" (the exact term is "exported") then it appears in the list in CE's memory viewer->view->enumerate dll and symbols.

To explain hooking, let's take the example of a big company that has a mailbox ("exported symbol/name" in a program) for each service, like purchases, investor relationships, accounting, customer service, etc... (functions for a program).
Hooking the accounting service is like removing the "accounting" sticker on the accounting service's mailbox and putting it on yours. When their mail arrives in your mailbox, you take it, read it, optionally tweak it, put it back in an envelope and drop it in the real accounting box. That's hooking.

How to do it? memory viewer->tools->auto assemble->template->any of the injection templates. Yes this is what they actually do, except that they do not always hook at the beginning of a function like in my example but somewhere in the middle.
As for the "api hook" template, it just removes the sticker for the original maibox and puts it somewhere, you have to make sure that this somewhere corresponds to your/a mailbox.

[kitesan]

thank you infinitely , extremely clear. do you know if this technique is also used for calling game's functions in game ? for example if i want to spawn a creature , i must call the game function that does that...

[Gniarf]

In a normal game, nothing is hooked. Hooking is typically used when you want to alter the behavior of another program, one that you did not write. For example hooking is used by AVs, malwares, DRMs, cracking tools, anticheats, cheats, and some mods. Overlays (like steam in-game) and directx manipulation tools (dxwnd and the likes) are also hooking some directx related functions.

If I wanted to make a hack that spawns a monsters I'd probably use hooking. It is likely that the mob spawner will want a pointer to an entity manager or an entity list so I'd hook a function that accesses it and call the spawner from my hook.
Or I could also hook the mob spawner itself so that each time it spawns something it also spawns my mob.