when use fstream in cplusplus, what's wrong with this program

Question

The next program what's wrong? I prefer the file reach the end.

ifstream file("main.cpp", ios::binary | ios::ate);
if (file) {
    //fstream::pos_type size = file.tellg();
    file.seekg(100, fstream::cur);
    if (file.eof()) {
        cout << "eof is true\n";
    }
}

fstream reach the end of the file, but why not echo "eof is true".

Answer 1

The eof bit is only set (and thus eof() only returns true) if an actual read operation fails due to hitting the end of the file. A seek operation (apparently) isn't enough.