Runtime patching in C++/inline assembly

Question

I am trying to patch the function cat() to return true, but for some reason the program crashes when I don't even call the function. Is the problem my method of patching? I think I am writing to the correct address (address of the function is 004012e4). I am using code blocks (gcc) on a Windows XP 32-bit system.

#include <iostream>
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
using namespace std;

int cat()
{
    cout<<"false"<<endl;
    return false;
}

int main()
{
    DWORD beef;
    int (*css)();
    css=cat;
    cout<<css<<endl;
    system("PAUSE");
    VirtualProtect(&css,49,PAGE_EXECUTE_READWRITE,&beef);
    asm("mov $0x40130f,%eax");//move address of the mov $0x0,eax instruction to eax
    asm("movl $0x1,(%eax)");//write at address changing B800 to B801 or return true

    return 0;
}

Answer 1

Why do you hardcode the function address? You have it in code, you are printing it out. If you print it and then change the code to include what you printed, you risk moving the function. Why not just generate the assembly statement dynamically?