There is an insightful question about reading a C/C++ data structure in C# from a byte array, but I cannot get the code to work for my collection of big-endian (network byte order) bytes. (EDIT: Note that my real struct has more than just one field.) Is there a way to marshal the bytes into a big-endian version of the structure and then pull out the values in the endianness of the framework (that of the host, which is usually little-endian)?
(Note, reversing the array of bytes will not work - each value's bytes must be reversed, which does not give you the same collection as reversing all of the bytes.)
This should summarize what I'm looking for (LE=LittleEndian, BE=BigEndian):
void Main()
{
var leBytes = new byte[] {1, 0, 2, 0};
var beBytes = new byte[] {0, 1, 0, 2};
Foo fooLe = ByteArrayToStructure<Foo>(leBytes);
Foo fooBe = ByteArrayToStructureBigEndian<Foo>(beBytes);
Assert.AreEqual(fooLe, fooBe);
}
[StructLayout(LayoutKind.Explicit, Size=4)]
public struct Foo {
[FieldOffset(0)]
public ushort firstUshort;
[FieldOffset(2)]
public ushort secondUshort;
}
T ByteArrayToStructure<T>(byte[] bytes) where T: struct
{
GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
T stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(),typeof(T));
handle.Free();
return stuff;
}
T ByteArrayToStructureBigEndian<T>(byte[] bytes) where T: struct
{
???
}
Other helpful links:
Byte of a struct and onto endian concerns
A little more on bytes and endianness (byte order)
Read binary files more efficiently using C#
As alluded to in my comment on @weismat's answer, there is an easy way to achieve big-endian structuring. It involves a double-reversal: the original bytes are reversed entirely, then the struct itself is the reversal of the original (big-endian) data format.
The fooLe and fooBe in Main will have the same values for all fields. (Normally, the little-endian struct and bytes wouldn't be present, of course, but this clearly shows the relationship between the byte orders.)
NOTE: See updated code including how to get bytes back out of the struct.
public void Main()
{
var beBytes = new byte[] {
0x80,
0x80,0,
0x80,0,
0x80,0,0,0,
0x80,0,0,0,
0x80,0,0,0,0,0,0,0,
0x80,0,0,0,0,0,0,0,
0x3F,0X80,0,0, // float of 1 (see http://en.wikipedia.org/wiki/Endianness#Floating-point_and_endianness)
0x3F,0xF0,0,0,0,0,0,0, // double of 1
0,0,0,0x67,0x6E,0x69,0x74,0x73,0x65,0x54 // Testing\0\0\0
};
var leBytes = new byte[] {
0x80,
0,0x80,
0,0x80,
0,0,0,0x80,
0,0,0,0x80,
0,0,0,0,0,0,0,0x80,
0,0,0,0,0,0,0,0x80,
0,0,0x80,0x3F, // float of 1
0,0,0,0,0,0,0xF0,0x3F, // double of 1
0x54,0x65,0x73,0x74,0x69,0x6E,0x67,0,0,0 // Testing\0\0\0
};
Foo fooLe = ByteArrayToStructure<Foo>(leBytes).Dump("LE");
FooReversed fooBe = ByteArrayToStructure<FooReversed>(beBytes.Reverse().ToArray()).Dump("BE");
}
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct Foo {
public byte b1;
public short s;
public ushort S;
public int i;
public uint I;
public long l;
public ulong L;
public float f;
public double d;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
public string MyString;
}
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct FooReversed {
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
public string MyString;
public double d;
public float f;
public ulong L;
public long l;
public uint I;
public int i;
public ushort S;
public short s;
public byte b1;
}
T ByteArrayToStructure<T>(byte[] bytes) where T: struct
{
GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
T stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(),typeof(T));
handle.Free();
return stuff;
}