Append Int to Data in Swift 3

Question

I am writing datagram for sending it to a server via UDP socket. How can I append Int to the end of a datagram (already composed Data)?

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Martin R · Accepted Answer · 2020-06-23T10:05:40.760

9

You can use the

public mutating func append<SourceType>(_ buffer: UnsafeBufferPointer<SourceType>)

method of Data. You probably also want to convert the value to network (big-endian) byte order when communicating between different platforms, and use fixed-size types like (U)Int16, (U)Int32, or (U)Int64.

Example:

var data = Data()

let value: Int32 = 0x12345678
var beValue = value.bigEndian
data.append(UnsafeBufferPointer(start: &beValue, count: 1))

print(data as NSData) // <12345678>

Update for Swift 4/5:

let value: Int32 = 0x12345678
withUnsafeBytes(of: value.bigEndian) { data.append(contentsOf: $0) }

The intermediate variable is no longer needed.

edited Jun 23 '20 at 10:05

answered Mar 06 '17 at 15:54

Martin R

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This gives me `Initialization of 'UnsafeBufferPointer' results in a dangling buffer pointer` – h345k34cr Jun 23 '20 at 09:18
@h345k34cr: Thanks for letting me know. I have added an updated version which should compile without problems. – Martin R Jun 23 '20 at 09:30

score 1 · Answer 2 · answered Jun 23 '20 at 09:22

1

Better way to do it:

var data = Data()
     
let value: Int32 = 0x12345678
var bigEndianVal = value.bigEndian

withUnsafePointer(to: &bigEndianVal) {
    data.append(UnsafeBufferPointer(start: $0, count: 1))
}

answered Jun 23 '20 at 09:22

h345k34cr

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Append Int to Data in Swift 3

2 Answers2