How to write byte(s) to a file in C++?

Question

I have created a bitset using std::bitset<8> bits which is equivalent to 00000000 i.e., 1 byte. I have output file defined as std::ofstream outfile("./compressed", std::ofstream::out | std::ofstream::binary) but when I write the bits using outfile << bits, the content of outfile becomes 00000000 but the size of file is 8 bytes. (each bit of bits end up taking 1 byte in the file). Is there any way to truly write byte to a file? For example if I write 11010001 then this should be written as a byte and the file size should be 1 byte not 8 bytes. I am writing a code for Huffman encoder and I am not able to find a way to write the encoded bytes to the output compressed file.

Answer 1

The issue is operator<< is the text encoding method, even if you've specified std::ofstream::binary. You can use put to write a single binary character or write to output multiple characters. Note that you are responsible for the conversion of data to its char representation.

std::bitset<8> bits = foo();
std::ofstream outfile("compressed", std::ofstream::out | std::ofstream::binary);

// In reality, your conversion code is probably more complicated than this
char repr = bits.to_ulong();

// Use scoped sentries to output with put/write
{
    std::ofstream::sentry sentry(outfile);
    if (sentry)
    {
        outfile.put(repr);                  // <- Option 1
        outfile.write(&repr, sizeof repr);  // <- Option 2
    }
}