在Swift中如何使用C中的Struct

swift 无法直接访问 c 语言的Struct。只能通过指针的方式访问。

///////－－－－－例子1开始－－－－－－－////////

The c Lib API : mycapi.h

<code style="margin: 0px; padding: 0px; border: 0px; font-family: Consolas,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",sans-serif; white-space: inherit;"><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">typedef</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">struct</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">{</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
    </span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,145,175);">int</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">  itype</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
    </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">double</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">*</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> dx</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
    </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">double</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">*</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> dy</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">}</span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjInfo</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">

</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">typedef</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjInfo</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">*</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjHandle</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">；</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">

</span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjHandle</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjInit</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">(</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">const</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">char</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">*</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">pFile</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">);</span></code>

add myapi.h as module

mySwiftcode :

normal; position: relative; overflow: auto; margin-top: 0px; margin-bottom: 1em; padding: 5px; border: 0px; font-size: 13px; width: auto; max-height: 600px; background-color: rgb(238,139);">import</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">Foundation</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0,139);">import</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> mycapiModule


var h</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">:</span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjHandle</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjInit</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">(</span><span class="str" style="margin: 0px; padding: 0px; border: 0px; color: maroon;">"/home/a"</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">)</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
var o</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">:</span><span class="typ" style="margin: 0px; padding: 0px; border: 0px; color: rgb(43,175);">MyObjInfo</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> h</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">.</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">memory
</span><span class="com" style="margin: 0px; padding: 0px; border: 0px; color: gray;">////to do somethings</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
</span><span class="com" style="margin: 0px; padding: 0px; border: 0px; color: gray;">//...</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
h</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">.</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">destroy</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">()</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;">
h </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> nil
print</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">(</span><span class="str" style="margin: 0px; padding: 0px; border: 0px; color: maroon;">"\(o.itype)"</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; color: black;">)</span></code>

///////－－－－－例子1结束－－－－－－－////////

在C函数定义的需要使用的Struct

typedef struct my_struct {
    unsigned char buffer[10];
} my_struct;

void my_struct_init(my_struct *my_s) {
    for (int i = 0; i < 10; i++) {
        my_s->buffer[i] = (char) i;
    }
}

In Swift,we have two options:

1. Struct on the stack

var my_s: my_struct = ...

However,we have to initialize it somehow. Every struct has a default initializer

var my_s: my_struct = my_struct(buffer: (0,0))

Note that in this case thebuffer[10]has been translated to Swift as a10-tuple.

Now we can call:

my_struct_init(&my_s)
println("Buffer: \(my_s.buffer)") // Buffer: (0,1,2,3,4,5,6,7,8,9)

ottom:1em; padding-top:0px; padding-bottom:0px; border:0px; font-size:15px; clear:both; color:rgb(34,the more complex is the struct,the more difficult is to use the default initializer.

2. Struct on the heap

This is similar to usingmallocandfreein C:

var my_s_pointer = UnsafeMutablePointer<my_struct>.alloc(1)
println("Buffer: \(my_s.buffer)") // Buffer: (some random values)

my_struct_init(my_s_pointer)
println("Buffer: \(my_s_pointer.memory.buffer)") // Buffer: (0,9)

my_s_pointer.destroy()

Combine both approaches

The following function will initialize any struct:

func initStruct<S>() -> S {
    let struct_pointer = UnsafeMutablePointer<S>.alloc(1)

    let struct_memory = struct_pointer.memory
    struct_pointer.destroy()

    return struct_memory
}

var my_s: my_struct = initStruct()
my_struct_init(&my_s)

C Struct 转义方法

funcblankof<T>(type:T.Type) ->T{

letptr =UnsafeMutablePointer<T>.alloc(sizeof(T))

letval = ptr.memory

ptr.destroy()

returnval

}

varfs =blankof(C_Struct)

test(&fs))

在bridging-header中 需要定义 在Swift中使用的Struct 文件。

Bridging-Header.h

<code style="margin: 0px; padding: 0px; border: 0px; font-family: Consolas,sans-serif; white-space: inherit;">#include "user_input.h"
</code>

user_input.c

#include <stdlib.h>

struct Pointer {
    int x;
    int y;
};

Pointer *create_pointer() {
    Pointer *p = malloc(sizeof(struct Pointer));
    if (p) {
        p->x = 20;
        p->y = 20;
    }
    return p;
}

void delete_pointer(Pointer *p) {
    free(p);
}

int pointer_x(Pointer *p) {
    return p->x;
}

int pointer_y(Pointer *p) {
    return p->y;
}

user_input.h

#ifndef __user_input_h__
#define __user_input_h__

typedef struct Pointer Pointer;
Pointer *create_pointer();
void delete_pointer(Pointer *p);
int pointer_x(Pointer *p);
int pointer_y(Pointer *p);

#endif

main.swift

normal; margin-top: 0px; margin-bottom: 1em; padding: 5px; border: 0px; font-size: 13px; overflow: auto; width: auto; max-height: 600px; background-color: rgb(238,sans-serif; white-space: inherit;">import Foundation

var pointer: copaquePointer = create_pointer()
println("\(pointer_x(pointer)),\(pointer_y(pointer))")
delete_pointer(pointer)

// Writing the wrapper class Could be helpful.

class CPointer {
    var _ptr: copaquePointer

    init() {
        _ptr = create_pointer()
        assert(_ptr,"Failed on create_pointer()")
    }

    deinit {
        delete_pointer(_ptr)
    }

    var x: Int {
        get { return Int(pointer_x(_ptr)) }
    }

    var y: Int {
        get { return Int(pointer_y(_ptr)) }
    }
}

var p = CPointer()
println("\(p.x),\(p.y)")</code>