UnsafeMutablePointer for array using in C library

Question

I want to implement C library into my iOS project. I'm using swift language.

I have a function where the input parameter - where output values are stored - is ar usual C double array:

double ar[6];
///...
 err = c_lib_func(ar);

If I initialize inside swift like var ar: [Double] xCode says I have to use

UnsafeMutablePointer. But inside the docs I haven't found how to initialize n-lenght array for UnsafeMutablePointer. I just can do something like this: var ar : UnsafeMutablePointer<Double>. But I can understand how to initialize it as 6-length array. Please, help me.

If I'm using

ar = [Double]
err = c_lib_func(ar);

the xCode shows to me this error:

/Users/admin/Documents/projects/myApp/myApp/file.swift:46:46: Cannot convert value of type '[Double]' to expected argument type 'UnsafeMutablePointer'

With var ar: [Double] you should be able to call c_lib_func(ar). — jtbandes
– jtbandes, Commented Mar 28, 2016 at 6:02
@jtbandes , no. xCode show the error about using UnsafeMutablePointer — Vyacheslav
– Vyacheslav, Commented Mar 28, 2016 at 6:03
Does using &ar to reference the underlying UnsafeMutablePointer work when ar is of type [Double]? — BallpointBen
– BallpointBen, Commented Mar 28, 2016 at 6:11

Robert Gummesson · Accepted Answer · 2016-03-28 10:30:30Z

1

In Swift, [Double] is an array of double values which is not what you are after. If you want to initialize an UnsafeMutablePointer you can just use:

var ar = UnsafeMutablePointer<Double>.alloc(6)

Use ar.dealloc(6) to release the memory again.

answered Mar 28, 2016 at 10:30

Robert Gummesson

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2 Comments

Vyacheslav Over a year ago

Is it important to use dealloc inside swift?

Robert Gummesson Over a year ago

Yes and it's also important that the value matches the value passed to alloc().

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