Fast Direct Memory Access

[fabiosa]

Hi,

The following should replace the word "Hello" in memory with "HHHHH".

I am just testing the following code so that I can understand how asm works, but I keep getting an unhandled memory exception when i get the 'mov byte ptr [eax], 048H' line.

I have tried to change it to 'move byte [eax], 048H' but it won't even compile.

// amtest.cpp : Defines the entry point for the application.
//

#include "stdafx.h"

void test(LPSTR,int);

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
     // TODO: Place code here.

    CHAR * szWord = "Hello";

    test ((LPSTR)szWord, sizeof(szWord));

    return 0;
}


void test(LPSTR ptrAddress, int len)
{
    
    _asm
    {
        pusha    //push all registers onto stack
        mov eax, [edi + 8] // load eax with ptrAddress
        mov ecx, [edi + 12] // load ecx with length of string (loop counter)
loop_start:
        mov byte ptr [eax], 048H //replace memory position with Ascii('H')
        inc eax //move to next memory location
        dec ecx //decrease counter
        jnz loop_start //loop
        popa //get registers back
    }

    return;
} 

If anyone could help me I would appreciate it. Thanks