c - change a pointer of address of another application

Question

I need somebody to edit the title, I can't find better title.

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Assume a have this simple program called source.exe:

#include <stdio.h>

int main()
{
   int a = 5;
   printf("%p", &a);
   return 0;
}

I want to write another application, change.exe, that changes a in the above.

I tried something like this:

int main()
{
   int * p = (int*) xxx; // xxx is what have printed above
   *p = 1;
   printf("%d", *p);
   return 0;
}

It doesn't work. assuming I have Administrator rights, is there a way to do what I've tried above? thanks.

Answer 1

In first place, when you run the second program, the a in the first will be long gone (or loaded in a different position). In second place, many OS's protect programs by loading them in separate spaces.

What you really seem to be looking for is Inter-Process Communication (IPC) mechanisms, specifically shared memory or memory-mapped files.