Converting unsigned int to byte array and back

Question

For a personal project of mine in C++ I've been looking into saving some data in a binary file. I did some research over Google and found several methods of doing this that more or less boiled down to the same thing. However, I cannot for the life of me get either the read or write method to work correctly. Any value I write, I get back differently. I've googled this extensively and looked across StackOverflow and I've not really found the solution so I'm starting to think I must be overlooking something, but I can't for the life of me figure out what.

Below the two methods in question for reading and writing an unsigned short.

unsigned short ReadUShort(std::ifstream& ifs)
{
    unsigned char buffer[2];

    ifs.read((char*)buffer, 2);
    unsigned short val = (buffer[0] << 8) | buffer[1];

    return val;
}

void WriteUShort(std::ofstream& ofs, unsigned short val)
{
    unsigned char buffer[2];

    buffer[0] = (val & 0xff);
    buffer[1] = ((val >> 8) & 0xff);

    ofs.write((char*)buffer, 2);
}

Thank you in advance for any and all help.

owacoder · Accepted Answer · 2016-03-08 16:32:21Z

2

Your read routine reads in big-endian order (most-significant byte first), and your write routine writes in little-endian order (least-significant byte first). You'll have to choose one or the other.

A big endian implementation:

unsigned short ReadUShort(std::ifstream& ifs)
{
    unsigned char buffer[2];

    ifs.read((char*)buffer, 2);
    unsigned short val = (buffer[0] << 8) | buffer[1];

    return val;
}

void WriteUShort(std::ofstream& ofs, unsigned short val)
{
    unsigned char buffer[2];

    //SWAPPED FROM LITTLE-ENDIAN TO BIG-ENDIAN
    buffer[0] = ((val >> 8) & 0xff); 
    buffer[1] = (val & 0xff);

    ofs.write((char*)buffer, 2);
}

answered Mar 8, 2016 at 16:32

owacoder

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2 Comments

Renegade Vile Over a year ago

slaps himself I can't believe I kept overlooking that.

Renegade Vile Over a year ago

I'd mark two correct answers if I could, as you're as correct as the poster above.

gmoniava · Accepted Answer · 2016-03-08 16:36:54Z

1

You have it reverse. Try this during read:

unsigned short val = ((unsigned short)buffer[1] << 8) | buffer[0];

edited Mar 8, 2016 at 16:36

answered Mar 8, 2016 at 16:32

gmoniava

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1 Comment

gmoniava Over a year ago

@RenegadeVile glad if this helped.

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