Writing binary data to fstream in c++ - c++

Question

Question
I have a few structures I want to write to a binary file. They consist of integers from cstdint, for example uint64_t. Is there a way to write those to a binary file that doesn not involve me manually splitting them into arrays of char and using the fstream.write() functions?
What I've tried
My naive idea was that c++ would figure out that I have a file in binary mode and << would write the integers to that binary file. So I tried this:
#include <iostream>
#include <fstream>
#include <cstdint>
using namespace std;
int main() {
fstream file;
uint64_t myuint = 0xFFFF;
file.open("test.bin", ios::app | ios::binary);
file << myuint;
file.close();
return 0;
}
However, this wrote the string "65535" to the file.
Can I somehow tell the fstream to switch to binary mode, like how I can change the display format with << std::hex?
Failing all that above I'd need a function that turns arbitrary cstdint types into char arrays.
I'm not really concerned about endianness, as I'd use the same program to also read those (in a next step), so it would cancel out.

Answer 1

Yes you can, this is what std::fstream::write is for:
#include <iostream>
#include <fstream>
#include <cstdint>
int main() {
std::fstream file;
uint64_t myuint = 0xFFFF;
file.open("test.bin", std::ios::app | std::ios::binary);
file.write(reinterpret_cast<char*>(&myuint), sizeof(myuint)); // or with recent C++: reinterpret_cast<std::byte*>
}