I have a library which contains this function:
void create_pointer(Pointer **pointer);
It takes a pointer's pointer and allocates memory for it. in c, I can do it like this
Pointer *pointer;
create_pointer(&pointer);
then I have a pointer's instance.
But now I want to use this function in Swift. How?
I have no details about Pointer, I only know it's a struct, defined like this
typedef struct Pointer Pointer;
Let's start with a C example
typedef struct {
NSUInteger someNumber;
} SomeStruct;
void create_some_struct(SomeStruct **someStruct) {
*someStruct = malloc(sizeof(SomeStruct));
(*someStruct)->someNumber = 20;
}
In C, you would use it like this:
//pointer to our struct, initially empty
SomeStruct *s = NULL;
//calling the function
create_some_struct(&s);
In Swift:
//declaring a pointer is simple
var s: UnsafePointer<SomeStruct> = UnsafePointer<SomeStruct>.null()
//well, this seems to be almost the same thing :)
create_some_struct(&s)
println("Number: \(s.memory.someNumber)"); //prints 20
Edit:
If your pointer is an opaque type (e.g. void *), you have to use
var pointer: COpaquePointer = COpaquePointer.null()
Note that Swift is not designed to interact with C code easily. C code is mostly unsafe and Swift is designed for safety, that's why the Swift code is a bit complicated to write. Obj-C wrappers for C libraries make the task much easier.
withUnsafePointer part. It doesn't seem to be necessary.