trouble converting unsigned int to byte array

[zsefv]

Hi, will need some pointers on how to approach this problem.

I need to convert a series of unsigned integers (which are from file) to a byte array so i can sent this byte array out via TCP socket.

I am having problems with converting, say 999 to 3e7. This is probably due to Java not having unsigned byte conversion. This is the method I am using.

	public static byte[] intToByteArray(int value, int byteSize) {
		byte[] b = new byte[byteSize];
		for (int i = 0; i < byteSize; i++) {
			int offset = (b.length - 1 - i) * 8;
			b[i] = (byte) ((value >>> offset) & 0xFF);
		}
		return b;
	}

This is not all that i am facing. After converting, I am supposed to concat these byte arrays before sending them out. The problem occurs when say i convert 15 into hexadecimal F, but i need 0F instead of just F to be concated to the byte array to be sent out. Is there anyway to prepend the 0 ?

[JosAH]

Read about the ByteBuffer class: In your case you put ints in it and get bytes out of it.

kind regards,

Jos

[zsefv]

i took your advice on using the ByteBuffer class, however am not really sure about the storing and retrieving of the data contained inside.

ByteBuffer tempArr = ByteBuffer.allocate(26);
tempArr.asShortBuffer().put((short) 80)
				.put((short) 255)
				.put((short) 255)
				.put((short) 255)
				.put((short) 255);

I allocated a buffer size then try to put the following inside : 0x50, 0xff, 0xff, 0xff, 0xff

tempArr.asShortBuffer().put((short)15);
tempArr.rewind();
while(tempArr.hasRemaining()){
     System.out.print(Integer.toHexString(tempArr.get()) + " ");
}

Then i added another 0x0f, and try to print out the data but i got this output:

0 f 0 ffffffff 0 ffffffff 0 ffffffff 0 ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

which is kinda strange, can someone please enlighten me?

[JosAH]

I don't know what you did, but I tried this quick little snippet:

import java.nio.ByteBuffer;

public class T {

	public static void main(String[] args) {

		ByteBuffer tempArr = ByteBuffer.allocate(6);
		
		tempArr.asShortBuffer().put((short)0x1234).put((short)0x2345).put((short)0x3456);
		tempArr.rewind();
		while (tempArr.remaining() > 0)
			System.out.printf("%02x\n", tempArr.get());

	}
}

... and it works fine. I didn't debug your code but I think the lengthening casts got you ;-)

kind regards,

Jos

[zsefv]

hi jos,

thanks for the assistance, can this ByteBuffer put like short, long consecutively?
my string of data is like this:

data[0] = f, -> 1 byte (unsigned char)
data[1] = 16, -> 2 bytes (unsigned short)
data[2] = 16, -> 1 byte (unsigned char)
data[3] = 3b, -> 1 byte (unsigned char)
data[4] = 3b, -> 1 byte (unsigned char)
data[5] = 3e7, -> 2 bytes (unsigned short)
data[6] = 5a, -> 2 bytes (short)
data[7] = 18fe7 -> 4 bytes (long)

so i just invoke the ByteBuffer put method by:

buf.asCharBuffer.put(data[0].charAt(0));
buf.asShortBuffer.put(data[1]);
etc etc
so is the unsigned portion being taken care off?

[JosAH]

hi jos,

thanks for the assistance, can this ByteBuffer put like short, long consecutively?

Read the API documentation for the ByteBuffer class; you can put/get all sorts of primitives (byte, short, int, long etc.) in/from the buffer.

kind regards,

Jos

ps. a long takes 8 bytes, an int takes 4 bytes.

[zsefv]

how about unsigned, signed data types?

[JosAH]

how about unsigned, signed data types?

There is no unsigned data type in Java but it doesn't matter much; just remove the sign extension wherever applicable, e.g. a byte value 0xff has its sign bits set when (implicitly) cast to an int: 0xffffffff.

kind regards,

Jos

[zsefv]

roger that jos,

many thanks , much appreciated

[JosAH]

roger that jos,

many thanks , much appreciated

You're welcome of course.

kind regards,

Jos