BitConverter.GetBytes in place

Question

I need to get values in UInt16 and UInt64 as Byte[]. At the moment I am using BitConverter.GetBytes, but this method give

Answer 1

You can do like this:

static unsafe void ToBytes(ulong value, byte[] array, int offset)
{
    fixed (byte* ptr = &array[offset])
        *(ulong*)ptr = value;
}

Usage:

byte[] array = new byte[9];
ToBytes(0x1122334455667788, array, 1);

You can set offset only in bytes.

If you want managed way to do it:

static void ToBytes(ulong value, byte[] array, int offset)
{
    byte[] valueBytes = BitConverter.GetBytes(value);
    Array.Copy(valueBytes, 0, array, offset, valueBytes.Length);
}

Or you can fill values by yourself:

static void ToBytes(ulong value, byte[] array, int offset)
{
    for (int i = 0; i < 8; i++)
    {
        array[offset + i] = (byte)value;
        value >>= 8;
    }
}