Question

I use an extension method to convert float arrays into byte arrays:

public static unsafe byte[] ToByteArray(this float[] floatArray, int count) {     int arrayLength = floatArray.Length > count ? count : floatArray.Length;     byte[] byteArray = new byte[4 * arrayLength];     fixed (float* floatPointer = floatArray)     {         fixed (byte* bytePointer = byteArray)         {             float* read = floatPointer;             float* write = (float*)bytePointer;             for (int i = 0; i < arrayLength; i++)             {                 *write++ = *read++;             }         }     }     return byteArray; } 

I understand that an array is a pointer to memory associated with information on the type and number of elements. Also, it seems to me that there is no way of doing a conversion from and to a byte array without copying the data as above.

Have I understood this? Would it even be impossible to write IL to create an array from a pointer, type and length without copying data?

EDIT: Thanks for the answers, I learned some fundamentals and got to try out new tricks!

After initially accepting Davy Landman’s answer I found out that while his brilliant StructLayout hack does convert byte arrays into float arrays, it does not work the other way around. To demonstrate:

[StructLayout(LayoutKind.Explicit)] struct UnionArray {     [FieldOffset(0)]     public Byte[] Bytes;      [FieldOffset(0)]     public float[] Floats; }  static void Main(string[] args) {     // From bytes to floats - works     byte[] bytes = { 0, 1, 2, 4, 8, 16, 32, 64 };     UnionArray arry = new UnionArray { Bytes = bytes };     for (int i = 0; i < arry.Bytes.Length / 4; i++)         Console.WriteLine(arry.Floats[i]);      // From floats to bytes - index out of range     float[] floats = { 0.1f, 0.2f, 0.3f };     arry = new UnionArray { Floats = floats };     for (int i = 0; i < arry.Floats.Length * 4; i++)         Console.WriteLine(arry.Bytes[i]); } 

It seems that the CLR sees both arrays as having the same length. If the struct is created from float data, the byte array’s length is just too short.

Answer 1

Yes, the type information and data is in the same memory block, so that is impossible unless you overwrite the type information in a float array to fool the system that it’s byte array. That would be a really ugly hack, and could easily blow up…

Here’s how you can convert the floats without unsafe code if you like:

public static byte[] ToByteArray(this float[] floatArray) {     int len = floatArray.Length * 4;     byte[] byteArray = new byte[len];     int pos = 0;     foreach (float f in floatArray) {         byte[] data = BitConverter.GetBytes(f);         Array.Copy(data, 0, byteArray, pos, 4);         pos += 4;     }     return byteArray; }