Mono Endianness

with .NET things are fairly simple - it is all (including ARM ASFAIK) running little endian .

The question that I have is: what is happing on Mono and (potentially) big endian systems? Do the bits reverse (when compared to x86)开发者_如何转开发 in Int32 / Int64 structure or does the framework force little endian rule-set?

Thanks

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Your assertion that all MS .NET are little endian is not correct. It depends on the architecture that you are running on - the CLR spec says so:

From the CLI Annotated Standard (p.161) — Partition I, section 12.6.3: "Byte Ordering":

For data types larger than 1 byte, the byte ordering is dependent on the target CPU. Code that depends on byte ordering may not run on all platforms. [...]

(taken from this SO answer)

See this answer for more information on the internals of BitConverter and how it handles endianness.

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A list of behavioral changes I can think of at the moment (unchecked and incomplete):

• IPAddress.HostToNetworkOrder and IPAddress.NetworkToHostOrder
• Nearly everything in BitConverter
• BinaryReader and BinaryWriter (EDIT: From documentation: "BinaryReader reads this data type in little-endian format.")
• Binary serialization
• Everything that reads and writes Unicode in default encoding from/to streams (UnicodeEncoding) (EDIT: Default is defined as little endian)

and of course every (runtime library) function using these.

Usually Microsoft doesn't mention endianness in their docs - with some strange exceptions. For instance, BinaryReader.ReadUInt16 is defined to read little endian. Nothing mentioned for the other methods. One may assume that binary serialization is always little-endian, even on big-endian machines.

Note that XNA on XBox360 is big-endian, so this not just a theoretical problem with Mono.

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c#/.Net does not make any claims on endian. int32/64 are atomic not structures.

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As far as I know such conversion would happen outside the scope of your code and hidden to you. It's called "managed code" for some reasons, including such potential issues.

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To know if bytes are "reversed", just check BitConverter.IsLittleEndian:

if (BitConverter.IsLittleEndian)
{
    // reverse bytes
}

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Considering how similar .Net and Mono are by design, I'd say they probably handle endianness the same.

You can always test it by creating a managed int with a known value, then using reflection or marshalling to access the memory and take a look.