Expressing a byte string

[DeptOfMeteors]

I need to know how to express a byte string literal in Java. I also need to compare it to a string of bytes that I'm reading from a file. I know how I'd do this in C. I'd have something like "\x000\x001\x002" (I think) then I'd then compare it with memcmp(). How do I do the same in Java?

[Eranga]

From where you find a byte string literal in Java?

[DeptOfMeteors]

If I could find one, I'm sure I could figure out how to make one.

[Eranga]

If I could find one, I'm sure I could figure out how to make one.

That's what I want to flag.

In C/C++ you can convert byte array to string in a sense that human can understand. If the byte array contain some annoying characters, by converting each you can build a meaningful string.

However Java doesn't have a direct way to do that.

[DeptOfMeteors]

So, what you're saying is if I wanted to find out if the first byte in a byte array was 8, and the next was 3, and the next was 2, while I could do

if (memcmp("\x08\x03\x02", pByteArray, 3) == 0)

in C, there isn't a one-liner in Java as simple that can accomplish this? Is the best I can do:

if (byteArray[0] == 8 && byteArray[1] == 3 && byteArray[2] == 2)

?

[Eranga]

As far as I know there is no any other way to do that.

[Fubarable]

C is a much more terse language than Java. It's also much easier to shoot yourself in the foot with C/C++.

[Eranga]

Even not .Net

[pbrockway2]

If you often have to check whether one array starts with elements equal to some other array you would write a method for that.

The array you are comparing with might be expressed, reasonabley tersely, as

new byte[] {8, 3, 2}

[Eranga]

So that method should have a way to convert values into a common format.

[pbrockway2]

So that method should have a way to convert values into a common format.

I'm not sure what you mean. I had in mind something like:

boolean compare(byte[] arr, byte[] with) {
    if(arr.length < with.length) {
        return false;
    }
    for(int i = 0; i < with.length; i++) {
        if(arr[i] != with[i]) {
            return false;
        }
    }
    return true;
}

Usage would be like:

//if (memcmp("\x08\x03\x02", pByteArray, 3) == 0)
if(compare(byteArray, new byte[] {8, 3, 2}))

[Eranga]

That's in same type. I thought in the other array there are string literals, with the number in another array (byte array actually)

[DeptOfMeteors]

Ok, now I've discovered another problem I'm going to have w/Java: no unsigned types. Quite literally, the line I have is:

private static byte[] _authenticationBytes = new byte[] { 0x01, 0x67, 0x22, 0x32, 0xa7, 0x0f, 0xef, 0x32, 0x65, 0x77, 0x62, 0x99, 0x88, 0x87, 0x11, 0x17 };

and my parser has flagged all those bytes >0x7f as errors. The recommendation is that they be cast to bytes. You now know that what I want to do is compare a byte array with another byte array, and I'm just wondering what's going to happen w/the bytes that are cast. Will they become negatives, and the ones that are 0x88 will remain 0x88, (and then somehow be internally imaged as -120) or will something else happen to them?

[JosAH]

Ok, now I've discovered another problem I'm going to have w/Java: no unsigned types. Quite literally, the line I have is:

private static byte[] _authenticationBytes = new byte[] { 0x01, 0x67, 0x22, 0x32, 0xa7, 0x0f, 0xef, 0x32, 0x65, 0x77, 0x62, 0x99, 0x88, 0x87, 0x11, 0x17 };

and my parser has flagged all those bytes >0x7f as errors. The recommendation is that they be cast to bytes. You now know that what I want to do is compare a byte array with another byte array, and I'm just wondering what's going to happen w/the bytes that are cast. Will they become negatives, and the ones that are 0x88 will remain 0x88, (and then somehow be internally imaged as -120) or will something else happen to them?

No problem; a narrowing cast simply chops of the bytes that won't fit, so e.g -88 stays -88, whether it's an int or a byte. Values that won't fit in a narrower type will be mutilated though, e.g 1024 (an int) will be zero as a byte.

kind regards,

Jos

[DeptOfMeteors]

That's the problem, I don't want these byte mutilated. So from what you are telling me, for all these bytes, the MSB will always be 0? So how do I express 88hex so that it'll be 10001000bin (notice the MSB set)?

-0x78

? (That's the right 2's complement representation, right?)