在iOS/MacOS中调用本机函数时，如何将复杂的快速数据类型传递给C数据类型？

Question

我成功地获得了一个基本的dylib，这个框架允许我传入一个Int，并返回和Int工作，但是我如何传递和返回更复杂的数据类型，比如指针、字节数组或实际的数据结构--从swift到C dylib？

是否有任何教程或资源可以将/pass/转换从快速数据类型映射为C数据类型，反之亦然，就像JNI中的java？

Answer 1

在Swift端解释C结构并动态提取c-dylib函数的示例如下所示：

.c文件

Person *get_person() {
    Person *p = malloc(sizeof(Person));
    p->first_name = strdup("Branford");
    p->last_name = strdup("Marsalis");
    p->age = 60;
    return p;
}

void free_person(Person *person) {
    free(person->first_name);
    free(person->last_name);
    free(person);
}

.h文件

typedef struct {
    char *first_name;
    char *last_name;
    int age;
} Person;

Swift

typealias getPersonFunc = @convention(c) () -> UnsafeMutablePointer<Person>
typealias freePersonFunc = @convention(c) (UnsafeMutablePointer<Person>) -> Void

...

let handle = dlopen("libsimple.dylib", RTLD_LOCAL|RTLD_NOW)
let get_person_sym = dlsym(handle, "get_person")
let getPerson = unsafeBitCast(get_person_sym, to: getPersonFunc.self)
let cPerson = getPerson()
let person = cPerson.withMemoryRebound(to: Person.self, capacity: 1) { $0.pointee }
let firstName = String(cString: UnsafeRawPointer(person.first_name).assumingMemoryBound(to: CChar.self))
let lastName = String(cString: UnsafeRawPointer(person.last_name).assumingMemoryBound(to: CChar.self))

print(firstName)
print(lastName)
print(person.age)

let free_person_sym = dlsym(handle, "free_person")
let freePerson = unsafeBitCast(free_person_sym, to: freePersonFunc.self)
freePerson(cPerson)

dlclose(handle)

测试

此示例的调试控制台上的输出如下所示：

Branford
Marsalis
60

从Swift到C

在.c中假设这一点：

void print_person(Person *person) {
    printf("%s %s is %d years old\n",
           person->first_name,
           person->last_name,
           person->age);
}

那么，在Swift方面，人们可以写：

typealias printPersonFunc = @convention(c) (UnsafeMutablePointer<Person>) -> Void
...
let newPerson = UnsafeMutablePointer<Person>.allocate(capacity: 1)
newPerson.pointee.first_name = UnsafeMutablePointer<Int8>(mutating: ("Norah" as NSString).utf8String)
newPerson.pointee.last_name = UnsafeMutablePointer<Int8>(mutating: ("Jones" as NSString).utf8String)
newPerson.pointee.age = 41
let print_person_sym = dlsym(handle, "print_person")
let printPerson = unsafeBitCast(print_person_sym, to: printPersonFunc.self)
printPerson(newPerson)
newPerson.deallocate()

这将在控制台上提供以下输出：

Norah Jones is 41 years old