Decimal to ByteArray & write to offset

Question

I want to know how I would convert from a decimal number located in a text box to hexadecimal and then to a byte array and write this array to the offset I want, using BinaryWriter.

My textBox11 decimal value is "101200001" and I need to write the it's Hexadecimal value, which is "06 08 30 81", into a file at a speciffic offset.

This is the what I have, but I'm missing the conversion from textBox11.Text to byteArray.

    int index = listBox1.SelectedIndex;
    int startOffset = 0x00000008;
    int itemIDDiff = 0x00000328;

    BinaryWriter bw = new BinaryWriter(File.Open(_FileName, FileMode.Open));
    bw.BaseStream.Seek(startOffset + itemIDDiff * index, SeekOrigin.Begin);
    bw.Write( /* textBox11.Text converted to HEX then to byte array? */ );
    bw.Close();

This is part of the file that I need to write to:

00000330h: 02 00 00 00 00 00 00 00 4A 61 64 65 20 45 61 72 ; ........Jade Ear
00000340h: 72 69 6E 67 00 00 00 00 00 00 00 00 00 00 00 00 ; ring............

let's say I want to change the "02 00 00 00" to "06 08 30 81". How would I do this using the BinaryWriter?

yamen · Accepted Answer · 2012-05-01T23:15:27.327

You can't convert decimal to Hex (how would you deal with the fraction portion?). But you can use Int64 (a long) instead:

var text = "101200001";
var asLong = Convert.ToInt64(text);
var asHex = asDecimal.ToString("X");

asHex now has the hex string you're after.

But the problem you have is that 'hex' is really just a way of viewing a set of raw bytes on disk. And the way a number is represented in raw bytes depends on the program itself. If you've got a binary writer, you just need to know the byte representation of the number you're trying to write. This may be enough by itself (without converting to string):

bw.Write(asLong);

Looked at this more, and it seems as though you're after 4-byte numbers, so ints not longs. BitConverter is good, but it writes everything in reverse order to what you may want. So keep these in mind and review the below:

var text = "101200001";
var asInt = Convert.ToInt32(text);                    // 4 byte number
var asBytes = BitConverter.GetBytes(asInt).Reverse(); // same hex representation as a byte array (same order)

And so in your example add this:

bw.Write(asBytes);

This is part of the file that I need to write to: 00000330h: 02 00 00 00 00 00 00 00 4A 61 64 65 20 45 61 72 ; ........Jade Ear 00000340h: 72 69 6E 67 00 00 00 00 00 00 00 00 00 00 00 00 ; ring............ lets say I want to change the "02 00 00 00" to "06 08 30 81", how would I do that? — Alan Alvarez, May 01 '12 at 23:12

score 3 · Answer 2 · answered May 01 '12 at 23:19

It isn't clear if little or big endian is required. Little endian is simple:

bw.Write(int.Parse(textBox11.Text));

For big endian as suggested in the question but unusual, you have to reverse the byte order:

var bytes = BitConverter.GetBytes(int.Parse(textBox11.Text));
Array.Reverse(bytes);
bw.Write(bytes);

Guffa · Answer 3 · 2012-05-01T23:15:55.203

You could convert the number into hexadecimal representation, then parse that, but that would be totally pointless.

You use the Int32.Parse method to parse the string into a number, then the BitConverter.GetBytes method to get the number as a byte array:

byte[] data = BitConverter.GetBytes(Int32.Parse(textBox11.Text));

Then you write the bytes to the stream:

bw.Write(data, 0, data.Length);

Note that this will write the bytes 81, 30, 08 06 to the stream on a system with little endian number representation, e.g. an Intel (or compatible) CPU based computer. If you want the big endian representation in the file, you would have to reverse the array before writing it:

Array.Reverse(data);

Decimal to ByteArray & write to offset

3 Answers3