C++ fstream writes garbage to file - c++

Question

The code below creates a vector that contains a vector of chars. It opens a fstream to a file. and then write the first char from the first vector. I tried to methods to write the char. Finally, I tried open a new 'fstream' and from it to print what I wrote. Both the printing and a simple inspection of the file shows it contian nothing, or sometimes garbage (dependening on the order of the writes). No errors or any weried output appear. I'm really loosing my mind over this.
#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
int main()
{
std::vector<char> y(6, 0);
y[0] = 1;
std::vector<std::vector<char>> vy;
vy.push_back(y);
std::fstream dateir("ffff.dat", std::ios::out | std::ios::out | std::ios::binary);
dateir<<vy[0][0] << endl;
int temp = vy[0][0];
dateir.write((char *)&temp, sizeof(int));
dateir.close();
cout << "here" << endl;
std::ifstream dateir2("ffff.dat", std::ios::out | std::ios::out | std::ios::binary);
if (dateir2.is_open())
{
std::cout << dateir2.rdbuf();
}
else{
cout << "no";
}
dateir2.close();
cout << "end";
return 0;
}

Answer 1

You have...a number of problems here.
std::fstream dateir("ffff.dat", std::ios::out | std::ios::out | std::ios::binary);
Is there a reason you've specified std::ios::out | std::ios::out? It's harmless, but clearly redundant.
As a first stab at things, I'd simplify the code a bit:
std::ofstream out("ffff.dat", std::ios::binary);
int data = 1;
out.write((char *)&data, sizeof(data));
out.close();
std::ifstream in("ffff.dat", std::ios::binary);
int data2;
in.read((char *)&data2, sizeof(data2));
if (data == data2) {
// what we read matched what we wrote
} else {
// what we read didn't match what we wrote
}
When you write binary data to a file, you usually want to just read it back in the way you wrote it out. If you want to look at the individual characters, you can do that but to get something that's semi-readable, you probably want to print them out in hexadecimal, or something on that order (and for this sort of exercise to mean much, you'd probably want to print it out in hex both before writing it out, and after reading it back in, to show they match, and let the reader see a reasonable understandable representation of the file contents).