C++ Converting char to byte array

Question

I need to be able to convert a QString in this format: "0x00 0x00 0x00 0x00"

To a byte array like this:

0x00,
0x00,
0x00,
0x00

I was able to do this in Visual Studio / C# like this:

byte[] bytes = string.Split(' ').Select(s => Convert.ToByte(s, 16)).ToArray();

However I am now using Qt / C++ and I need a way to do the same thing. What would be the easiest way to do this?

LogicStuff · Accepted Answer · 2015-12-23 12:06:11Z

5

Not the most concise solution, but at least safe, I guess (invalid values are not appended):

QString string = "0x00 0x00 0x00 0x00";
QByteArray bytes;

for(auto const& x : string.split(' '))
{
    bool ok;
    uint val = x.toUInt(&ok, 16);

    if(ok && val <= 0xff)
        bytes.append(static_cast<char>(val));
}

This might be faster (invalid values are left equal to 0):

QString string = "0x00 0x00 0x00 0x00";
QStringList list = string.split(' ');
QByteArray bytes(list.size(), '\0');

for(size_t i = 0; i < list.size(); ++i)
{
    bool ok;
    uint val = list[i].toUInt(&ok, 16);

    if(ok && val <= 0xff)
        bytes[i] = static_cast<char>(val);
}

You can omit the check in both cases, if all you want is speed.

edited Dec 23, 2015 at 12:06

answered Dec 23, 2015 at 11:38

LogicStuff

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2 Comments

RobbieE Over a year ago

Your second option will be faster but initialising the byte array is wasteful since all bytes will be set in the for loop anyway.

LogicStuff Over a year ago

There's if, they might not. The point of the second snippet is that there's no reallocation of the array.

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