C#

// This method takes data type T and stores it into a byte array starting at the specified index.
// The caller specifies whether the Most Significant Byte (MSB) should be stored at byteArray[index].
// If MSBFirst is false, then the MSB will be stored at byteArray[index + sizeof(T) - 1]
// This method assumes that we are running on a PC which is little endian.
public unsafe static void IntoBytes2 <T> (byte[] byteArray, int index, T data, bool MSBFirst) where T : struct
{
    byte* dataPtr = (byte*)&data;

    // make sure the array is big enough for the type being stored.
    if ((index + sizeof(T) - 1) <= byteArray.Length)
    {
        if (MSBFirst)
            // Reverse the Endianess
            for (int i = index + sizeof(T) - 1; i >= index; i--, dataPtr++)
            {
                byteArray[i] = *dataPtr;
            }
        else
            // Same endianess of platform (little on PC)
            for (int i = index; i < index + sizeof(T); i++, dataPtr++)
            {
                byteArray[i] = *dataPtr;
            }
    }
}