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)

• John Montgomery: Can you add the exact text of the errors you're getting, and the details of the Buffer struct?
• Martin R: My guess: buffer should be initialized and not an optional.
• Deepak Sharma: It should be initialized to something, like all values 0?

Answer 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)