Create a 16 byte array of zeros in swift

Question

I have to initialize a 16 byte array of Zeros in my Swift Project. In Java its easy to initialize 16 byte array using following code:

new byte[16]

I need the same code implementation in Swift. Thanks a lot in advance for any help. Have a good day!

What have you tried already? Please post your work-in-progress implementation. — JAL
– JAL, Commented Apr 6, 2016 at 18:45
So, you want to know how to create an array of zero bytes. You should edit your question to reflect just that, instead of the encryption stuff you have mentioned. — Debosmit Ray
– Debosmit Ray, Commented Apr 6, 2016 at 18:51
Hi @JAL , I have tried to initialize variable of type UInt16 in swift as Byte in swift is typedef to UInt16. But when I try to print its size using sizeofValue, it always returns 8 bytes instead of 16. — Navdeep Singh Rana
– Navdeep Singh Rana, Commented Apr 6, 2016 at 19:03
"as Byte in swift is typedef to UInt16" – ???? There is no Byte type in Swift 2.2. There is UInt8 though ... What exactly did you do with sizeofValue? — Martin R
– Martin R, Commented Apr 6, 2016 at 19:06
@MartinR I had a variable of type UInt8 and Uint16 but when I print it using print(sizeofValue(variable)) I get 8 bytes instead of 16 bytes but what I need is a 16 byte array — Navdeep Singh Rana
– Navdeep Singh Rana, Commented Apr 6, 2016 at 19:57

Community · Accepted Answer · 2017-05-23 11:50:38Z

6

Use an UnsafeMutablePointer. I'd imagine UInt8 is probably closest to Java's byte, so you can allocate space for 20 of those and initialize them to0 like so...

let ptr = UnsafeMutablePointer<UInt8>.alloc(20)
ptr.initialize(0)

Edit: Thanks to vacawama

You can also use a Swift array and the & operator to convert it to a pointer, which is syntactically a bit nicer...

var arr = [UInt8](count: 20, repeatedValue: 0)
doSomething(&arr)

These two methods are functionally equivalent as & will convert the array to an UnsafeMutablePointer under the hood.

Note: Notice that I used the var keyword to define the array in the second example, so that the & operator converts it to UnsafeMutablePointer instead of UnsafePointer. Otherwise, you will get a cryptic compiler error if you attempt to mutate the memory

edited May 23, 2017 at 11:50

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answered Apr 6, 2016 at 19:06

Charlie Martin

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9 Comments

dfrib Over a year ago

Out of curiosity (never really used pointers in Swift), when would you prefer the method above over just using a "safe native" array of UInt8 elements (readily transferable to NSData, if we'd so wish)? E.g. let foo = [UInt8](count: 20, repeatedValue: 0).

Charlie Martin Over a year ago

You would always prefer the swift Array since its memory will be managed for you. However, there are times (like when you are interfacing with C code) that you need a pointer as opposed to a Swift object in which case you must use UnsafeMutablePointer. For example, you cannot call a C function which takes a pointer as an argument with a native swift type. It's not mentioned explicitly in the question, but I had kind of assumed he needs a pointer since the java equivalent provided will be a pointer.

dfrib Over a year ago

I see, it was an honest inquiry and not a pointer (no pun intended), thanks!

vacawama Over a year ago

@CharlieMartin, I disagree with your assertion that you need to create the array as an UnsafeMutablePointer to interact with C. You can pass a UInt8 array as &arrayName. See developer.apple.com/library/ios/documentation/Swift/Conceptual/…

vacawama Over a year ago

The &arr can only appear in a call argument list. You can't do let ptr = &arr, but you can call a C function void doSomething(unsigned char *str) from Swift with doSomething(&arr).

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orion elenzil · Accepted Answer · 2025-06-01 04:31:48Z

2

Just freshening @Charlie Martin's answer for 2025,

let array = [UInt8](repeating: 0, count: 16)

// or if you're into Data

let data = Data([UInt8](repeating: 0, count: 16))

answered Jun 1 at 4:31

orion elenzil

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