How to turn machine code into binary executable?

Question

I'm writing a very small x86 assembler which currently outputs hex (or binary, it'd be trivial to change) machine code. How can I write this hex/binary into a file that I can actually execute?

For a simple input like:

mov ax, #1
ret

the assembler would output:

66b80100
c3

Answer 1

To append hex values to a binary in C++, you have to represent it as its raw int value and write that to the file.

Thus:

void writeHexStringToFile(string hex, ofstream& file) {
    vector<string> hexBytes = hexBytesFromString(hex);
    for (unsigned i = 0; i < hexBytes.size(); i++) {
        istringstream buff(hexBytes.at(i));
        int hexVal;
        buff >> hex >> hexVal;
        file.write(reinterpret_cast<char*>(&hexVal), sizeof(int));
    }
}