How do I move back X bytes from the end of a file and edit it? (Using ofstream in c++)

All I want to do is move the 'put' pointer from the end of the file to a point 'X' bytes behind the end of the file.

#include <iostream>
#include <fstream>
using namespace std;
int main(){
    ofstream ofile;
    //Assuming "file.dat" does not exist
    ofile.open("file.dat", ios::binary|ios::app);
    int x = 12;
    ofile.write((char*) &x, sizeof(int));
    ofile.seekp(-4, ios::cur);
    x = 10;
    ofile.write((char*) &x, sizeof(int));
    ofile.close();

    x = 0;
    ifstream ifile("file.dat", ios::binary);
    ifile.read((char*) &x, sizeof(int));
    cout<<x; //This line should display 10
    return 0;
}

However, the output displays 12...

Image of output here...

I read many articles on StackOverflow, which did mention that to 'seek' the 'put' pointer, I must use 'ios::ate', and not 'ios::app'.

But I even tried using the following instead, and I still had no luck...

 ofile.open("file.dat", ios::binary|ios::ate);

Is what I'm doing wrong? Is there another way to move the 'put' pointer back as such?

This is just the simpler version of what was not working in the project I need to make for school...

Any help will be appreciated... Thank you...