Question

我在Bridging-Header.h

中声明了一个C ++函数

struct MyFloat3{
    float x;
    float y;
    float z;
};
struct MyFloat3 ExtCurl(const float** triangle);

我已按照http://www.swiftprogrammer.info/swift_call_cpp.html的说明进行操作 wrapper.cpp

#include "Curl.h"
extern "C" MyFloat3 ExtCurl(const float** triangle){
    return Curl(triangle);
}

Curl.h

struct MyFloat3{
    float x;
    float y;
    float z;
};
MyFloat3 Curl(const float** triangle);

Curl.cpp

#include "Curl.h"
MyFloat3 Curl(const float** triangle){
  MyFloat3 curl;
  curl.x = (triangle[1][1] - triangle[0][1])*(triangle[2][2]-triangle[0][2]) - (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]);
  curl.y = (triangle[1][2] - triangle[0][2])*(triangle[2][0]-triangle[0][0]) - (triangle[1][0] - triangle[0][0])*(triangle[2][2]-triangle[0][2]);
  curl.z = (triangle[1][0] - triangle[0][0])*(triangle[2][1]-triangle[0][1]) - (triangle[1][1] - triangle[0][1])*(triangle[2][0]-triangle[0][0]);
  return curl;
}

我试图从我的快速代码中调用它

var triangle:[[Float]] = [
            [1.0, 0.0, 0.8],
            [0.0, 0.5, 0.0],
            [4.0, 0.0, 6.0]
        ]
var normal:MyFloat3
normal = ExtCurl(triangle)

编译器骂

Node.swift:127:38: Cannot convert value of type '[[Float]]' to
expected argument type 'UnsafeMutablePointer<UnsafePointer<Float>?>!'

我的C ++库的另一个函数返回void但通过给它的指针填充数组工作正常

Answer 1

在Swift中，使用由指针指针表示的嵌套C数组并不容易。正如预期的类型UnsafeMutablePointer<UnsafePointer<Float>?>!所暗示的那样，您需要创建一个UnsafePointer<Float>?数组，并将指针传递给数组。

在你的情况下，像这样：

let triangle:[Float] = [
    1.0, 0.0, 0.8,
    0.0, 0.5, 0.0,
    4.0, 0.0, 6.0
]

var normal = triangle.withUnsafeBufferPointer {(buffer)->MyFloat3 in
    let rowCount = 3
    var rowPointers: [UnsafePointer<Float>?] = [
        buffer.baseAddress,
        buffer.baseAddress!+rowCount,
        buffer.baseAddress!+rowCount*2
    ]
    return ExtCurl(&rowPointers)
}

（假设您的ExtCurl没有保留指针以备将来使用。）

Answer 2

let triangle0: [[Float]] = [
    [1,2,3],
    [10,20,30],
    [100,200,300]]

let normal = triangle0.flatMap{ $0 }.withUnsafeBufferPointer { (buffer) -> float3 in
    var p = buffer.baseAddress
    return ExtCurl(&p)
}

更新以查看差异（对于OOPer）

let triangle:[Float] = [
    1.0, 0.0, 0.8,
    0.0, 0.5, 0.0,
    4.0, 0.0, 6.0
] 
let normal = triangle.withUnsafeBufferPointer { (buffer) -> float3 in
    var p = buffer.baseAddress
    return ExtCurl(&p)
}

使用工作示例（Swift，C ++）更新//

main.swift

var triangle:[[Float]] = [
    [1.0, 0.0, 0.8],
    [0.0, 0.5, 0.0],
    [4.0, 0.0, 6.0]
]

triangle.flatMap{ $0 }.withUnsafeBufferPointer {(buffer)->() in
    var p = buffer.baseAddress
    let normal = fc(&p)
    print("from Swift:", normal)
}

引诱-桥接-Header.h

struct float3 {
    float x;
    float y;
    float z;
};

struct float3 fc(const float **);

test2.hpp

#ifndef test2_hpp
#define test2_hpp

#include <stdio.h>

struct float3CPP {
    float x;
    float y;
    float z;
};

struct float3CPP fcpp(const float **);

extern "C" struct float3CPP fc(const float ** p) {
    return fcpp(p);
};

#endif /* test2_hpp */

测试2.cpp

#include "test2.hpp"

struct float3CPP fcpp(const float ** triangle) {
    float3CPP curl;
    curl.z = (triangle[1][0] - triangle[0][0])*(triangle[2][1]-triangle[0][1]) - (triangle[1][1] - triangle[0][1])*(triangle[2][0]-triangle[0][0]);
    curl.y = (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]) - (triangle[1][0] - triangle[0][0])*(triangle[2][2]-triangle[0][0]);
    curl.x = (triangle[1][1] - triangle[0][1])*(triangle[2][2]-triangle[0][2]) - (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]);
    return curl;
}

打印

from Swift: float3(x: 111856.898, y: -3.65359902e+24, z: 3.86805511e+24)
Program ended with exit code: 0

正如所料......

请检查三角形[x] [y]中的值...没有您希望看到的内容： - ）

所以你唯一的麻烦就是如何将float ** p转换为t [3] [3]

struct float3CPP fcpp(const float **t) {

    float triangle[3][3];
    for( int i = 0; i < 9; i++) {
        int row = i / 3;
        int col = i % 3;
        triangle[row][col] = *(*t + i);
    };


    float3CPP curl;

    curl.z = (triangle[1][0] - triangle[0][0])*(triangle[2][1]-triangle[0][1]) - (triangle[1][1] - triangle[0][1])*(triangle[2][0]-triangle[0][0]);
    curl.y = (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]) - (triangle[1][0] - triangle[0][0])*(triangle[2][2]-triangle[0][0]);
    curl.x = (triangle[1][1] - triangle[0][1])*(triangle[2][2]-triangle[0][2]) - (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]);


    return curl;
}

会返回您想要的

from Swift: float3(x: 2.5999999, y: 5.0, z: -1.5)
Program ended with exit code: 0

更新2 如果你将c ++函数定义为

struct float3CPP fcpp2(float triangle[3][3]) {

    float3CPP curl;

    curl.z = (triangle[1][0] - triangle[0][0])*(triangle[2][1]-triangle[0][1]) - (triangle[1][1] - triangle[0][1])*(triangle[2][0]-triangle[0][0]);
    curl.y = (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]) - (triangle[1][0] - triangle[0][0])*(triangle[2][2]-triangle[0][0]);
    curl.x = (triangle[1][1] - triangle[0][1])*(triangle[2][2]-triangle[0][2]) - (triangle[1][2] - triangle[0][2])*(triangle[2][1]-triangle[0][1]);

    return curl;
};

你的c ++头文件将是

struct float3CPP fcpp2(float t[3][3]);
extern "C" struct float3CPP fc2(float t[3][3]) {
    return fcpp2(t);
};

使用桥接标题

struct float3 {
    float x;
    float y;
    float z;
};

struct float3 fc2(float [][3]);

和主要的swift

let triangle:[[Float]] = [
    [1.0, 0.0, 0.8],
    [0.0, 0.5, 0.0],
    [4.0, 0.0, 6.0]
]

var t2 = triangle.reduce([]) { (r, row) -> [(Float, Float, Float)] in
    var r = r
    r.append((row[0], row[1], row[2]))
    return r
}

t2.withUnsafeMutableBufferPointer { (buffer) -> () in
    var p = buffer.baseAddress
    let normal = fc2(p)
    print("from Swift fc2:", normal)
}

打印正确的结果

from Swift fc2: float3(x: 2.5999999, y: 5.0, z: -1.5)
Program ended with exit code: 0

更新3 “最好”的方式，怎么做，就是将c ++函数声明为

// parameter is pointer to array of array 3 of const float
struct float3CPP fcpp3(const float (* const t)[][3]) {
    return fcpp2(*t);
}

更新标题....并在Swift中使用它

let triangle:[[Float]] = [
    [1.0, 0.0, 0.8],
    [0.0, 0.5, 0.0],
    [4.0, 0.0, 6.0]
]
triangle.flatMap{ $0 }.withUnsafeBufferPointer {(buffer)->() in
    let normal3 = fc3(OpaquePointer(buffer.baseAddress))
    print("from Swift fc3:", normal)
}

打印出正确的结果： - ）

from Swift fc3: float3(x: 2.5999999, y: 5.0, z: -1.5)
Program ended with exit code: 0

如何从swift中将一个float数组数组传递给C ++函数

2 个答案: