How to read a value of an hard coded address in C++?

Question

I am looking to read the value that is located in address 302H. The purpose is to read an input from hardware (a part of a 104pc stack). When I run the following code a get this error: Unhandled exception at 0x004134b9 in setOutput.exe: 0xC0000005: Access violation reading location 0x00000302.

#include <stdlib.h> 

#define PORTBASE 0x302
int _tmain(int argc, char *argv[])
{
    int value;
    int volatile * port = (int *) PORTBASE;
    printf("port = %d\n", port);
    value = *port;
    printf("port value = %d\n", value);
}

EDIT:

I am running this under widows xp. Only Documentation I can find on the board is below

EDIT:

From your answers below, I can see that I need to write a driver for the board. Can someone point me to a resource on how to do so?

Answer 1

In order to access physical memory directly under Windows, you need to develop a driver. I suggest you read up on Virtual Address Space to see why. The short story: The memory addresses you see from a usermode process has no relation to physical memory addresses, and the addresses where hardware lives are protected by the OS to prevent usermode applications from messing up things.