如何在Swift中使用htonl设置整数字节序？

Question

I'm trying to set integer endianness using htonl() in Swift but the compiler isn't finding the htonl() method.

I've been using this as my reference: Append NSInteger to NSMutableData

Here's my code:

import Foundation
import CFNetwork
import CoreFoundation

var data = NSMutableData()
var number : UInt32 = 12
var convertedNumber : UInt32 = htonl(number)
data.appendBytes(&convertedNumber, length: 4)

I've just been running this in a playground. The error is:

Use of unresolved identifier 'htonl'

Answer 1

As of Xcode 6, Beta 3, all integer types have a bigEndian method which returns the big-endian representation of the integer and changes the byte order if necessary. Example:

var data = NSMutableData()
var number : UInt32 = 0x12345678
var convertedNumber = number.bigEndian
data.appendBytes(&convertedNumber, length: 4)
print(data)
// Output: <12345678>

Update for Swift 3:

let data = NSMutableData()
let number: UInt32 = 0x12345678
var convertedNumber = number.bigEndian
data.append(&convertedNumber, length: 4)

Or, using the new Data value type:

var data = Data()
let number: UInt32 = 0x12345678
var convertedNumber = number.bigEndian
withUnsafePointer(to: &convertedNumber) {
    data.append(UnsafeRawPointer($0).assumingMemoryBound(to: UInt8.self), count: 4)
}

Answer 2

Update : Martin R's answer is the correct answer for current versions of Swift: https://stackoverflow.com/a/24653879/195691

--

You should use the CFSwapInt32HostToBig() CoreFoundation method, as htonl is likely implemented as a C macro that will not work in swift.

However, it looks like this doesn't currently work in the Swift playground. I'm getting the error Playground execution failed: error: error: Couldn't lookup symbols: __OSSwapInt32 despite the fact that the CoreFoundation documentation now includes method signatures in Swift for its byte swapping methods.

Interestingly, it looks like at least part of <arpa/inet.h> has been ported to swift, as methods like inet_ntoa() and inet_addr() are available to Swift, but the htonl family is not.

Answer 3

Instead of using CFSwapInt32HostToBig() as Alex Pretzlav advised you should use

CFSwapInt32()

instead of

ntonl() and ntohl()

and

CFSwapInt16()

instead of

ntons() and ntohs()

Your code should look like

import Foundation
import CFNetwork
import CoreFoundation

var data = NSMutableData()
var number : UInt32 = 12
var convertedNumber : UInt32 = CFSwapInt32(number)
data.appendBytes(&convertedNumber, length: 4)

Also there is

CFSwapInt64()

for 8-byted integer swapping.

Edit 1

Of course you should use these functions only on processors with little endian integers cause functions I provided perform bytes swap anyway.