C#调用DLL各种传参

C++#define JNAAPI extern "C" __declspec(dllexport) // C方式导出函数

typedef struct
{
    int osVersion;
    int majorVersion;
    int minorVersion;
    int buildNum;
    int platFormId;
    char szVersion[128];
}OSINFO;  

// 1. 获取版本信息(传递结构体指针)
JNAAPI bool GetVersionPtr( OSINFO *info );
// 2.获取版本信息(传递结构体引用)
JNAAPI bool GetVersionRef(OSINFO &info);

C#

// OSINFO定义
[StructLayout(LayoutKind.Sequential)]
public struct OSINFO
{
	public int osVersion;
	public int majorVersion;
	public int minorVersion;
	public int buildNum;
	public int platFormId;
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
	public string szVersion;
}

1. 方式一(传入结构体引用),在C#中,结构体是以传值方式传递,类才是以传地址方式传递,加关键字ref即可. C端传递了两种不同类型的参数,都可以通过引用来解决.

[DllImport("jnalib.dll", EntryPoint = "GetVersionPtr")]
public static extern bool GetVersionPtr(ref OSINFO info);
public static extern bool GetVersionRef(ref OSINFO info);

2. 方式二(传入IntPtr(平台通用指针))

IntPtr pv = Marshal.AllocHGlobal(148); //结构体在使用时一定要分配空间(4*sizeof(int)+128)
Marshal.WriteInt32(pv,148); //向内存块里写入数值
if (GetVersionPtr(pv)) //直接以非托管内存块地址为参数
{
	Console.WriteLine("--osVersion:{0}", Marshal.ReadInt32(pv, 0));
	Console.WriteLine("--Major:{0}",Marshal.ReadInt32(pv, 4)); //移动4个字节
	Console.WriteLine("--BuildNum: " + Marshal.ReadInt32(pv, 12));
	Console.WriteLine("--szVersion: "+Marshal.PtrToStringAnsi((IntPtr)(pv.ToInt32()+20)));
}
Marshal.FreeHGlobal(pv); //处理完记得释放内存

二.结构体数组的传递

C++

// 传递结构体指针
JNAAPI bool GetVersionArray(OSINFO *info,int nLen);

C#

/**
 * C#接口,对于包含数组类型,只能传递IntPtr
 */
[DllImport("jnalib.dll", EntryPoint = "GetVersionArray")]
public static extern bool GetVersionArray(IntPtr p, int nLen);  

// 源目标参数
OSINFO[] infos = new OSINFO[2];
for (int i = 0; i < infos.Length; i++)
{
	infos[i] = new OSINFO();
}

IntPtr[] ptArr = new IntPtr[1];
ptArr[0] = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(OSINFO)) * 2); //分配包含两个元素的数组
IntPtr pt = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(OSINFO)));
Marshal.Copy(ptArr, 0, pt, 1); //拷贝指针数组
GetVersionArray(pt, 2); //调用

//还原成结构体数组
for (int i = 0; i < 2; i++)
{
	infos[i]=(OSINFO)Marshal.PtrToStructure((IntPtr)(pt.ToInt32()+i*Marshal.SizeOf(typeof(OSINFO))),typeof(OSINFO));
	Console.WriteLine("OsVersion:{0} szVersion:{1}", infos[i].osVersion, infos[i].szVersion);
}

三. 复杂结构体的传递

C++

typedef struct
{
	char name[20];
	int age;
	double scores[30];
}Student;

// Class中包含结构体数组类型
typedef struct
{
	int number;
	Student students[50];
}Class;

// 传入复杂结构体测试
JNAAPI int GetClass(Class *pClass,int len);

C#

// 接口定义
[DllImport("jnalib.dll", EntryPoint = "GetClass")]
public static extern int GetClass(IntPtr pv,int len);

// 结构体定义
// Student
[StructLayout(LayoutKind.Sequential)]
public struct Student
{
	[MarshalAs(UnmanagedType.ByValTStr,SizeConst=20)]
	public string name;
	public int age;
	[MarshalAs(UnmanagedType.ByValArray, SizeConst = 30)]
	public double[] scores;
}

// Class
[StructLayout(LayoutKind.Sequential)]
public struct Class
{
	public int number;
	[MarshalAs(UnmanagedType.ByValArray, SizeConst = 50)] // 指定数组尺寸
	public Student[] students; // 结构体数组定义
}

// 调用复杂结构体测试
int size = Marshal.SizeOf(typeof(Class)) * 50;
IntPtr pBuff = Marshal.AllocHGlobal(size); // 直接分配50个元素的空间,比Marshal.copy方便多了
GetClass(pBuff, 50);

Class[] pClass = new Class[50];
for (int i = 0; i < 50; i++)
{
	IntPtr ptr = new IntPtr(pBuff.ToInt64() + Marshal.SizeOf(typeof(Class)) * i);
	pClass[i] = (Class)Marshal.PtrToStructure(ptr, typeof(Class));
}
Marshal.FreeHGlobal(pBuff); // 释放内存

2. 输入参数, 给复杂结构体赋值后作为输入参数传入

对于比较大的结构体指针,无法直接应用结构体类型,转化成IntPtr类型, 此时需要将原生类型转化为指针,并给指针赋值

调用方法: Marshal.StructureToPtr(stu, ptr1, true)