Swift Xcode6B3 - Byte Swapping - Undefined symbol "__OSSwapInt16" - xcode

Question

I wanted to use the Swift method CFSwapInt16BigToHost but I can't get it linking. I link against the CoreFoundation framework, but every time I get the following error :
Undefined symbols for architecture i386:
"__OSSwapInt16", referenced from:
Did I miss something ?

Answer 1

Yes, for some reason the CFSwap... functions cannot be used in a Swift program.
But since Xcode 6 beta 3, all integer types have little/bigEndian: constructors
and little/bigEndian properties.
From the UInt16 struct definition:
/// Creates an integer from its big-endian representation, changing the
/// byte order if necessary.
init(bigEndian value: UInt16)
/// Creates an integer from its little-endian representation, changing the
/// byte order if necessary.
init(littleEndian value: UInt16)
/// Returns the big-endian representation of the integer, changing the
/// byte order if necessary.
var bigEndian: UInt16 { get }
/// Returns the little-endian representation of the integer, changing the
/// byte order if necessary.
var littleEndian: UInt16 { get }
Example:
// Data buffer containing the number 1 in 16-bit, big-endian order:
var bytes : [UInt8] = [ 0x00, 0x01]
let data = NSData(bytes: &bytes, length: bytes.count)
// Read data buffer into integer variable:
var i16be : UInt16 = 0
data.getBytes(&i16be, length: sizeofValue(i16be))
println(i16be) // Output: 256
// Convert from big-endian to host byte-order:
let i16 = UInt16(bigEndian: i16be)
println(i16) // Output: 1
Update: As of Xcode 6.1.1, the CFSwap... functions are available in Swift, so
let i16 = CFSwapInt16BigToHost(bigEndian: i16be)
let i16 = UInt16(bigEndian: i16be)
both work, with identical results.

Answer 2

It looks like those are handled with a combination of macro's and inline functions so... I don't know why it wouldn't be already statically compiled into the CF version:
generally to solve this kind of dependency riddle you can just search for the naked function name without prefixed underscores, then figure out where it should be linked from
#define OSSwapInt16(x) __DARWIN_OSSwapInt16(x)
then
#define __DARWIN_OSSwapInt16(x) \
((__uint16_t)(__builtin_constant_p(x) ? __DARWIN_OSSwapConstInt16(x) : _OSSwapInt16(x)))
then
__DARWIN_OS_INLINE
__uint16_t
_OSSwapInt16(
__uint16_t _data
)
{
return ((__uint16_t)((_data << 8) | (_data >> 8)));
}
I know this isn't a real answer but it was too big for a comment,
I think you may need to find out if there is a problem with the way that swift imports the headers... like if for instance the macro's to import headers isn't correct in a swift setup.

Answer 3

As the other answers have pointed out, the __OSSwapInt16 swap method does not appear to be in the swift header of the CFByte framework. I think the swift like alternative would be:
var dataLength: UInt16 = 24
var swapped = UInt16(dataLength).byteSwapped