Typecast UnsafeMutablePointer<Void> to UnsafeMutablePointer<#Struct type#>

Question

I created a struct in Swift called RGB, simple enough:

struct PixelRGB { var r: CUnsignedChar = 0 var g: CUnsignedChar = 0 var b: CUnsignedChar = 0 init(red: CUnsignedChar, green: CUnsignedChar, blue: CUnsignedChar) { r = red g = green b = blue } }

And I have a pointer var imageData: UnsafeMutablePointer<PixelRGB>!.

I wish to malloc some space for this pointer, but malloc returns UnsafeMutablePointer<Void> and I cannot cast it like below:

imageData = malloc(UInt(dataLength)) as UnsafeMutablePointer<PixelRGB> // 'Void' is not identical to `PixelRGB`

Anyway to solve this? Thank you for your help!

How about imageData = UnsafeMutablePointer<PixelRGB>.alloc(dataLength)? — matt
– matt, Commented Sep 24, 2014 at 0:37
You would only malloc it if it needs to have a dynamic lifetime. Otherwise, why don't you just have a variable of type PixelRGB? — newacct
– newacct, Commented Sep 24, 2014 at 19:01

matt · Accepted Answer · 2014-09-24 01:01:37Z

20

I think what you want to say is something like this:

imageData = UnsafeMutablePointer<PixelRGB>.alloc(dataLength)

answered Sep 24, 2014 at 1:01

matt

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4 Comments

Antwan van Houdt Over a year ago

@AntonHolmquist imageData.destroy()

eofster Over a year ago

@AntonHolmquist The opposite of alloc() is dealloc(). The destroy() method is the counterpart of initialize().

Fooberman Over a year ago

This answer is a better way to solve the OPs problem, but it does not answer the question asked in the title. Either the title should change, or someone should answer the question about type casting.

matt Over a year ago

@Fooberman I'm not sure what you're after here, but feel free to supply your own answer to the original question.

Ahmed · Accepted Answer · 2014-12-05 00:21:18Z

Have you tried the following?

imageData = unsafeBitCast(malloc(UInt(dataLength)), UnsafeMutablePointer<PixelRGB>.self)

Ref: Using Legacy C APIs with Swift

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