Executing the following code

#include <iostream>
#include <fstream>

int main() {
    std::fstream fs{"/dev/shm/test.bin", std::ios::in | std::ios::out | std::ios::binary | std::ios::trunc};
    std::cerr << "open: "<<  fs.is_open()
              << " good:" << fs.good()
              << " tellg: "<< fs.tellg()
              << " tellp: " << fs.tellp() 
              << std::endl;
    
    fs.write("123", 2);

    std::cerr << "open: "<<  fs.is_open()
              << " good:" << fs.good()
              << " tellg: "<< fs.tellg()
              << " tellp: " << fs.tellp() 
              << std::endl;

    return 0;
}

Prints

open: 1 good:1 tellg: 0 tellp: 0
open: 1 good:1 tellg: 2 tellp: 2

Why does tellg() change? Shouldn’t tellg still be 0 since I have not performed any reads?