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, Menlo, Monaco, "Lucida Console", "Liberation Mono", "DejaVu Sans Mono", "Bitstream Vera Sans Mono", "Courier New", monospace, sans-serif; white-space: inherit;"><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0, 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, 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, 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, 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, 145, 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, 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, 145, 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, 145, 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, 145, 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, 145, 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, 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, 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

my Swift code :

<code style="margin: 0px; padding: 0px; border: 0px; font-family: Consolas, Menlo, Monaco, "Lucida Console", "Liberation Mono", "DejaVu Sans Mono", "Bitstream Vera Sans Mono", "Courier New", monospace, sans-serif; white-space: inherit;"><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; color: rgb(0, 0, 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, 145, 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, 0, 139);">import</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; color: black;"> mycapiModulevar 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, 145, 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, 145, 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, 145, 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, 0, 0, 0, 0, 0, 0, 0, 0))

Note that in this case the buffer[10] has been translated to Swift as a 10-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)

However, the more complex is the struct, the more difficult is to use the default initializer.

2. Struct on the heap

This is similar to using malloc and free in 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, 1, 2, 3, 4, 5, 6, 7, 8, 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.memorystruct_pointer.destroy()return struct_memory
}var my_s: my_struct = initStruct()
my_struct_init(&my_s)

C Struct 转义方法

func blankof<T>(type:T.Type) ->T {

let ptr =UnsafeMutablePointer<T>.alloc(sizeof(T))

let val = ptr.memory

ptr.destroy()

return val

}

var fs =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, Menlo, Monaco, "Lucida Console", "Liberation Mono", "DejaVu Sans Mono", "Bitstream Vera Sans Mono", "Courier New", monospace, 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

<code style="margin: 0px; padding: 0px; border: 0px; font-family: Consolas, Menlo, Monaco, "Lucida Console", "Liberation Mono", "DejaVu Sans Mono", "Bitstream Vera Sans Mono", "Courier New", monospace, sans-serif; white-space: inherit;">import Foundationvar 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: COpaquePointerinit() {_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>

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