fstream std::ios::binary printing in ASCII ? is it working correctly?

Question

i was trying to write some data to a file in binary, the following is the minimal reproducible example of the problem, i am trying to print two unsigned 64 bit integers to a binary file and read one of them again ... problem is that the data is not printed or read in binary.

#inclue <fstream>
#include <iostream>
#include <stdint.h>
#include <iomanip>

int main()
{
    uint64_t a = 1;
    uint64_t b = 2;
    uint64_t c;
    std::ofstream s("file.bin", std::ios::out | std::ios::binary);
    s << a << b;
    s.close();
    std::ifstream in("file.bin", std::ios::in | std::ios::binary);
    in >> c;
    in.close();
    std::cout << c << '\n';

    std::cin >> c;
    return 0;
}

the ouput of the above code is 12, so i checked the file using notepad, and it had 12 written in it in ASCII, not in binary, i am using the latest version of msvc2017 on windows, i tried compiling it for x86 and x64, in debug and release mode and the error persists.

so is this its intended behavior ? and do i need to cast every variable to an array of characters when printing and reading ?

Answer 1

The stream input and output operators >> and << are text-based. They will write the output as text, and read the input as text. Even for binary files.

To write raw binary data use the write function. And to read the raw binary data use read:

s.write(reinterpret_cast<char const*>(&a), sizeof a);
s.write(reinterpret_cast<char const*>(&b), sizeof b);

// ...

in.read(reinterpret_cast<char*>(&c), sizeof c);