Pass pointer to var in C function from Swift

Question

I have a C function in a file with name (Buffer is a C struct)

   BufferInit(Buffer *buffer, int32_t size)

As I am moving to Swift, in my Swift class I declare a private var like

 var buffer:Buffer?

and in init function I make a call like this

  BufferInit(&buffer, 32)

But I get compilation errors, what is the correct way to achieve the same in Swift? I call call the same BufferInit from Objective-C without issues but Swift is messy.

EDIT: Here are details,

       typedef struct {
         void             *buffer;
         int32_t           length;
         int32_t           tail;
         int32_t           head;
        } Buffer;

Error is compiler is asking me to unwrap buffer and correct the code as(which I don't think is correct):

       BufferInit(&buffer!, 32)

Can you add the exact text of the errors you're getting, and the details of the Buffer struct? — John Montgomery
– John Montgomery, Commented Apr 27, 2017 at 18:02
My guess: buffer should be initialized and not an optional. — Martin R
– Martin R, Commented Apr 27, 2017 at 18:05

Martin R · Accepted Answer · 2017-04-27 18:23:58Z

1

Your C function is imported to Swift as

func BufferInit(_ buffer: UnsafeMutablePointer<Buffer>!, _ size: Int32)

and you have to pass the address of a (initialized, nonoptional) variable of type Buffer as an inout expression. Structures imported from C have a default constructor in Swift which initializes all members to zero, so you can write

var buffer = Buffer()
BufferInit(&buffer, 32)

edited Apr 27, 2017 at 18:23

answered Apr 27, 2017 at 18:09

Martin R

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