Question

I was working on a piece of code to do some compression, and I wrote a bitstream class.

My bitstream class kept track of the current bit we are reading and the current byte (unsigned char).

I noticed that reading the next unsigned character from the file was done differently if I used the >> operator vs get() method in the istream class.

I was just curious why I was getting different results?

ex:

this->m_inputFileStream.open(inputFile, std::ifstream::binary);   
unsigned char currentByte;
this->m_inputFileStream >> currentByte;

vs.

this->m_inputFileStream.open(inputFile, std::ifstream::binary);
unsigned char currentByte;
this->m_inputFileStream.get((char&)currentByte);

Additional Info:

To be specific the byte I was reading was 0x0A however when using >> it would read it as 0x6F

I’m not sure how they’re even related ? (they’re not the 2s complement of each other?)

The >> operator is also defined to work for unsigned char as well however (see c++ istream class reference

Answer 1

If you aren’t parsing text, don’t use operator>> or operator<<. You’ll get weird bugs that are hard to track down. They are also resilient to unit tests, unless you know what to look for. Reading a uint8 for instance will fail on 9 for instance.

edit:

#include <iostream>
#include <sstream>
#include <cstdint>

void test(char r) {
        std::cout << "testing " << r << std::endl;
        char t = '!';
        std::ostringstream os(std::ios::binary);
        os << r;
        if (!os.good()) std::cout << "os not good" << std::endl;
        std::istringstream is(os.str(), std::ios::binary);
        is >> t;
        if (!is.good()) std::cout << "is not good" << std::endl;
        std::cout << std::hex << (uint16_t)r 
             << " vs " << std::hex << (uint16_t)t << std::endl;
}

int main(int argc, char ** argv) {
        test('z');
        test('\n');
        return 0;
}

produces:

testing z
7a vs 7a
testing 

is not good
a vs 21

I suppose that would never have been evident a priori.