Pass an UnsafeMutableRawPointer as a function parameter

Question

When I try to pass an UnsafeMutableRawPointer as a function parameter I get the following error:

A C function pointer can only be formed from a reference to a 'func' or a literal closure

Specifically this is from the following code:

public func sqlite3_bind_text(_ oP: OpaquePointer!, _ first: Int32, _ second: UnsafePointer<Int8>!, _ third: Int32, _ ptrs: ((UnsafeMutableRawPointer?) -> Void)!) -> Int32 {
    SQLite3.sqlite3_bind_text(oP, first, second, third, ptrs)
}

I've looked at: How to use instance method as callback for function which takes only func or literal closure but can't see how I can apply that to my situation.

How can I pass the pointer through my function?

func sqlite3_bind_text(_: OpaquePointer!, _: Int32, _: UnsafePointer!, _: Int32, _: ((UnsafeMutableRawPointer?) -> Void)!) -> Int32 — WishIHadThreeGuns, Oct 20 '20 at 19:07
You have to add “@convention(c)” to the parameter declaration of your wrapper function as well: `_ ptrs: (@convention(c) (UnsafeMutableRawPointer?) -> Void)!` – But what is the point of defining a function with the same signature as `SQLite3.sqlite3_bind_text` and forwarding the call? — Martin R, Oct 20 '20 at 19:09
Note that the last parameter is not a UnsafeMutableRawPointer but a pointer to a function (which takes a UnsafeMutableRawPointer parameter). — Martin R, Oct 20 '20 at 19:32

score 1 · Accepted Answer · answered Oct 20 '20 at 19:22

SQLite is a pure C library, and SQLite3.sqlite3_bind_text() takes a pointer to a C function as the fifth parameter. Such a parameter is marked with @convention(c) and that must be replicated in your wrapper function:

public func sqlite3_bind_text(_ oP: OpaquePointer!, _ first: Int32,
                              _ second: UnsafePointer<Int8>!,
                              _ third: Int32,
                              _ ptrs: (@convention(c) (UnsafeMutableRawPointer?) -> Void)!) -> Int32 {
    SQLite3.sqlite3_bind_text(oP, first, second, third, ptrs)
}

Pass an UnsafeMutableRawPointer as a function parameter

1 Answers1