获取结构的地址

Question

这是我的代码:

using System.Collections;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;
using System;
using System.IO;

public class CarMove : MonoBehaviour
{
public unsafe struct TrafficRoadSystem { };
public unsafe struct CarsSimulation { };
public unsafe struct CarPostion
{
    double position_x;
    double position_y;
    double position_z;
};

// Use this for initialization
[DllImport("Assets/traffic.dll", CharSet = CharSet.Ansi)]
public unsafe static extern int traffic_import_osm([MarshalAs(UnmanagedType.LPStr)] string osm_pbf_path, TrafficRoadSystem** out_road_system);
[DllImport("Assets/traffic.dll")]
public unsafe static extern int create_simulation(TrafficRoadSystem* road_system, CarsSimulation** out_simulation, double speed, int cars_count);
[DllImport("Assets/traffic.dll")]
public static extern void update_simulation(ref CarsSimulation simulation, double time);
[DllImport("Assets/traffic.dll")]
public static extern CarPostion get_car_postion(ref CarsSimulation simulation, int car_number);
unsafe CarsSimulation* carSimulation;
unsafe TrafficRoadSystem* trafficRoadSystem;
void Start()
{
    unsafe
    {
        string osmPath = "Assets/Resources/map.osm.pbf";
        int results;
        results = traffic_import_osm(osmPath, &trafficRoadSystem);
    }
}

// Update is called once per frame
void Update()
{

}
}

这是来自dll C库.函数作为参考int traffic_import_osm()在TrafficRoadSystem* trafficRoadSystem;对象上工作,我想访问对象 void Update().这在一个函数中运行良好,但我无法得到类变量的地址,我得到错误

Error CS0212 You can only take the address of an unfixed expression inside of a fixed statement initializer

排队 results = traffic_import_osm(osmPath, &trafficRoadSystem);

我尝试使用此解决方案 https://msdn.microsoft.com/en-us/library/29ak9b70(v=vs.90).aspx

我写了这个:

TrafficRoadSystem trafficRoadSystem;
void Start()
{
    unsafe
    {
        string osmPath = "Assets/Resources/map.osm.pbf";
        CarMove carMove = new CarMove();
        int results;
        fixed( TrafficRoadSystem* ptr = &carMove.trafficRoadSystem)
        {
            results = traffic_import_osm(osmPath, &ptr);
        }
    }
}

我得到错误CS0459 Cannot take the address of a read-only local variable的行 results = traffic_import_osm(osmPath, &ptr);

Answer 1

在Unity中制作C或C++插件需要对这些语言有广泛的了解.这意味着在尝试在Unity中使用原始指针之前,您应该花时间学习指针.因为即使你编译它,你也可能遇到很难修复崩溃.

你有:

unsafe TrafficRoadSystem* trafficRoadSystem;

并希望将其传递给下面的函数:

public unsafe static extern int traffic_import_osm(..., TrafficRoadSystem** out_road_system);

1个 .The trafficRoadSystem变量是一个指针,你将需要另一个指针指向trafficRoadSystem.这被称为"指针指针"

TrafficRoadSystem** addressOfTrafficRoadSystem = &trafficRoadSystem;

注意双" **".

2,你必须使用fixed关键字来做我在#1中提到的事情.

fixed (TrafficRoadSystem** addressOfTrafficRoadSystem = &trafficRoadSystem)
{

}

3.您可以将指针传递给traffic_import_osm函数的指针地址.

全新的Start功能:

void Start()
{
    unsafe
    {
        fixed (TrafficRoadSystem** addressOfTrafficRoadSystem = &trafficRoadSystem)
        {
            string osmPath = "Assets/Resources/map.osm.pbf";
            int results;
            results = traffic_import_osm(osmPath, addressOfTrafficRoadSystem);
        }
    }
}

未来可能出现的相关问题:

1,我注意到你CarMove carMove = new CarMove();在更新的问题中做了.不要在new这里使用关键字,因为CarMove继承自MonoBehaviour.请参阅此答案以了解该怎么做.

2,我也注意到你用过了"Assets/Resources/map.osm.pbf";.构建项目时,此路径无效.考虑使用StreamingAssets文件夹而不是仅适用于ResourcesAPI 的Resources文件夹.您Application.streamingAssetsPath与StreamingAssets文件夹一起使用.