Programming Forums > Application Development > C++

Klarre · Nov 16th, 2005, 12:32 PM

I am trying to call this function using inline assembly:

BOOL GetCursorPos(LPPOINT lpPoint);

I began doing it using C++, and it works fine, using this code:

(Toggle Plain Text)

#include <windows.h>
int main()
{
	// C++
	while(true)
	{
		POINT cursorPos;
		GetCursorPos(&cursorPos);
	}

	return 0;
}

But now I wish to do the same thing using inline assembly. I found it a little bit trickier!

My thoughts were - "It want an adress to a struct that only contains two int's (actually long's). How do I do this?" I wrote this code...

(Toggle Plain Text)

#include <windows.h>

int main()
{
	// Assembly
	while(true)
	{
		int cursorPos[2];
		cursorPos[0] = cursorPos[1] = 0;

		_asm
		{
			lea eax, cursorPos
			push eax
			call GetCursorPos
		}
	}

	return 0;
}

...but Visual Studio gives me this error: "Unhandled exception at 0x0042e484 in test.exe: 0xC0000005: Access violation writing location 0xfffffed0." And it comes when calling the GetCursorPos.

Where did my thoughts went wrong? Thanks for your help!

/Klarre

nnxion · Nov 16th, 2005, 1:24 PM

Uhmm POINT is a structure, which contains an x and a y coordinate. GetCursorPos will give you a structure back. I'm not sure how to do that, but that's what's going wrong if I'm not mistaken.

Polyphemus_ · Nov 16th, 2005, 1:45 PM

I'm definitely not an assembly expert, but can't you do just this:

(Toggle Plain Text)

	while(true) {
		POINT cursorPos;

		_asm {
			push cursorPos
			call GetCursorPos
		}
	}

@nnxion: Using an array or POINT doesn't really matter i believe, in the end it are just two integers.

Klarre · Nov 16th, 2005, 2:23 PM

Quote:

Originally Posted by Polyphemus_

I'm definitely not an assembly expert, but can't you do just this:

(Toggle Plain Text)

	while(true) {
		POINT cursorPos;

		_asm {
			push cursorPos
			call GetCursorPos
		}
	}

@nnxion: Using an array or POINT doesn't really matter i believe, in the end it are just two integers.

Actually this code should not be used inline (I am just coding inline because it is easier to debug). Therefor I can not make use of any structs or classes.
Your proposal do not work. But thanks anyway!

/Klarre

nnxion · Nov 16th, 2005, 2:38 PM

You are just coding inline because it is easier to debug? That's the most ridiculous statement I have ever heard about inline assembly.

Klarre · Nov 16th, 2005, 2:55 PM

Quote:

Originally Posted by nnxion

You are just coding inline because it is easier to debug? That's the most ridiculous statement I have ever heard about inline assembly.

Oh! Haha!

I guess I forgot to tell you that I am working on an assembly application. I am just testing my code inline before I implement it in the real app!

/Klarre

Klarre · Nov 16th, 2005, 6:29 PM

Problem solved!

Found that it is possible to create structs in asm. That helped alot!

/Klarre

nnxion · Nov 17th, 2005, 12:37 PM

Quote:

Originally Posted by Polyphemus_

@nnxion: Using an array or POINT doesn't really matter i believe, in the end it are just two integers.

Well there's the overhead of a structure which will make it different from just two integers.

Nov 16th, 2005, 12:32 PM	#1
Klarre Game engine designer Join Date: May 2005 Location: Sweden Posts: 318 Rep Power: 4	[WIN32] Inline asm call to GetCursorPos I am trying to call this function using inline assembly: (Toggle Plain Text) BOOL GetCursorPos(LPPOINT lpPoint); BOOL GetCursorPos(LPPOINT lpPoint); I began doing it using C++, and it works fine, using this code: (Toggle Plain Text) #include <windows.h> int main() { // C++ while(true) { POINT cursorPos; GetCursorPos(&cursorPos); } return 0; } #include <windows.h> int main() { // C++ while(true) { POINT cursorPos; GetCursorPos(&cursorPos); } return 0; } But now I wish to do the same thing using inline assembly. I found it a little bit trickier! My thoughts were - "It want an adress to a struct that only contains two int's (actually long's). How do I do this?" I wrote this code... (Toggle Plain Text) #include <windows.h> int main() { // Assembly while(true) { int cursorPos[2]; cursorPos[0] = cursorPos[1] = 0; _asm { lea eax, cursorPos push eax call GetCursorPos } } return 0; } #include <windows.h> int main() { // Assembly while(true) { int cursorPos[2]; cursorPos[0] = cursorPos[1] = 0; _asm { lea eax, cursorPos push eax call GetCursorPos } } return 0; } ...but Visual Studio gives me this error: "Unhandled exception at 0x0042e484 in test.exe: 0xC0000005: Access violation writing location 0xfffffed0." And it comes when calling the GetCursorPos. Where did my thoughts went wrong? Thanks for your help! /Klarre

Nov 16th, 2005, 1:24 PM	#2
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	Uhmm POINT is a structure, which contains an x and a y coordinate. GetCursorPos will give you a structure back. I'm not sure how to do that, but that's what's going wrong if I'm not mistaken. __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

Nov 16th, 2005, 1:45 PM	#3
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	I'm definitely not an assembly expert, but can't you do just this: (Toggle Plain Text) while(true) { POINT cursorPos; _asm { push cursorPos call GetCursorPos } } while(true) { POINT cursorPos; _asm { push cursorPos call GetCursorPos } } @nnxion: Using an array or POINT doesn't really matter i believe, in the end it are just two integers.

Nov 16th, 2005, 2:38 PM	#5
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	You are just coding inline because it is easier to debug? That's the most ridiculous statement I have ever heard about inline assembly. __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

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Nov 16th, 2005, 6:29 PM	#7
Klarre Game engine designer Join Date: May 2005 Location: Sweden Posts: 318 Rep Power: 4	Problem solved! Found that it is possible to create structs in asm. That helped alot! /Klarre

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Programming Forums > Application Development > C++

[WIN32] Inline asm call to GetCursorPos