如何获得指向字符串的持久指针？

Question

I found String 's generic instance method withCString(_:) , but I need to get pointers to multiple strings and don't want to have a bunch of nested closures. For example, let's say that str1 and str2 are both String instances, foo and bar are both C struct types, and do_something is a C function. Then how do I do something like this?

let ptr1 = str1.pointerThatPersistsEvenAfterPassedToFunction
let ptr2 = str2.pointerThatPersistsEvenAfterPassedToFunction
let c_struct1 = foo(ptr1, 1, 2)
let c_struct2 = bar(ptr2, 3, c_struct1)
do_something(c_struct1, c_struct2)
str1.invalidatePersistentPointer
str2.invalidatePersistentPointer

Answer 1

You cannot safely access a Swift String 's underlying buffer without using withCString .

So you can either use the nested closures which is the safest and most correct way to use the CString s or you can use UnsafeMutablePointer<CChar> and allocate and manage the CString s yourself.