[Source] Hooking ! [Series part 0]

#include <iostream>
#include <windows.h>


void __stdcall hook(DWORD Timeout){   

	/*
	since the caller (the one with the Sleep() in his code) does not know that the function is hooked
	We have access to all the arguments that the function has. We can change and display them before passing on execution,
	or we can even prevent the function from being executed!
	*/

	printf("No rest for the wicked! not even %d seconds!\n",(int) (Timeout/1000));  // display the timeout in milliseconds

return;  // we wont execute the Sleep() function at all, No rest for the wicked!
}

DWORD *GetPointer()
{	
	DWORD* func;
_asm{
	lea eax, Sleep           // note: lea = Load Extended Address		 moving the address of the pointer to eax
	mov func, eax			 // note: mov = Move 					     now we have the address of the pointer in Func
	}

	return func;

}
DWORD* Tfunc = GetPointer();    //i think that's the Sleep pointer
DWORD* DoHook(DWORD* hook){

/*
Here *func (what func points to) still points to the address of sleep.
We however, don't want it to point there, we want it to point to our hook function.
Therefore we're going to change it, this can be done without any modifications to our virtual memory access.
Because the pointers are kept in our .data section, and we have write permission in our .data section.
*/DWORD* func = GetPointer();
	

	*func = (DWORD) hook;      // change what *func points to, remeber that func is the same pointer as used in the call dword[addfress] instruction.                
	return func;

}

void UnHook()
{	DWORD* func = GetPointer();
	
	*func = (DWORD)Tfunc;
	
}

int main(){

	DWORD* Hooked;

printf("Sleeping for 2 seconds!\n");
Sleep(2000);   // sleep is in milliseconds 1/1000th second therefore 2000 = 2 seconds
printf("Done sleeping!\n");



Hooked = DoHook((DWORD*)&hook);                       // now detour Sleep()!

printf("Sleeping for 3 seconds!\n");
Sleep(3000);
printf("Done sleeping!\n");

printf("Unhooking...\n");
UnHook();
printf("Done...Sleeping for 3sec\n");
Sleep(3000);
printf("Done");

std::cin.ignore();
	return 0;
}