C#总结（七）动态加载C++动态链接库

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C#调用C++ 链接库的方式分为静态调用和动态调用这两种方式。静态调用之前的文章里面都有介绍，使用.net 提供的DllImport 导入相关的C++ 库即可。请看之前的文章，https://www.cnblogs.com/zhangweizhong/p/8119340.html 。

今天介绍动态调用的方法。很多时候，Dll库的目录可能是变化的，或是有些场景，需要根据具体的情况，来动态加载这些Dll库。这样使用静态调用的方式就很不方便，C#中我们经常通过配置动态的调用托管Dll，那么是不是也可以这样动态调用C++动态链接呢？
只要通过LoadLibrary, GetProcess, FreeLibrary这几个函数是可以动态调用动态链接的（它们包含在kernel32.dll中）。

原理

LoadLibrary ( string lpFileName)：载入指定的动态链接库，并将它映射到当前进程使用的地址空间。载入成功后即可访问库内保存的资源，除了LoadLibrary 方法，还有一个类似的 LoadLibraryEx 方法。

GetProcAddress (int hModule, string lpProcName)：GetProcAddress函数检索指定的动态链接库(DLL)中的输出库函数地址。如果函数调用成功，返回值是DLL中的输出函数地址。如果函数调用失败，返回值是NULL。调用函数GetLastError ，得到具体的错误信息。

FreeLibrary ( int hModule) ：释放指定的动态链接库，它们早先是用LoadLibrary API函数装载的。

GetLastError() ：获取错误信息

实现

1. 将kernel32中的几个方法封装成本地调用类 DLLWrapper

using System;
using System.IO;
using System.Runtime.InteropServices;

namespace Irisking.Basic.Util
{
    /// <summary>
    /// DLLWrapper
    /// </summary>
    internal class DLLWrapper
    {
        [DllImport("kernel32.dll")]
        private static extern uint GetLastError();


        /// <summary>
        /// API LoadLibraryEx
        /// </summary>
        /// <param name="lpFileName"></param>
        /// <param name="hReservedNull"></param>
        /// <param name="dwFlags"></param>
        /// <returns></returns>
        [DllImport("kernel32.dll", EntryPoint = "LoadLibraryEx", SetLastError = true)]
        private static extern int LoadLibraryEx(string lpFileName, IntPtr hReservedNull, LoadLibraryFlags dwFlags);

        /// <summary>
        /// API GetProcAddress
        /// </summary>
        /// <param name="handle"></param>
        /// <param name="funcname"></param>
        /// <returns></returns>
        [DllImport("Kernel32", EntryPoint = "GetProcAddress", SetLastError = true)]
        public static extern int GetProcAddress(int handle, string funcname);

        /// <summary>
        ///  API FreeLibrary
        /// </summary>
        /// <param name="handle"></param>
        /// <returns></returns>
        [DllImport("Kernel32", EntryPoint = "FreeLibrary", SetLastError = true)]
        private static extern int FreeLibrary(int handle);

        ///<summary>
        /// 通过非托管函数名转换为对应的委托 , by jingzhongrong
        ///</summary>
        ///<param name="dllModule"> 通过 LoadLibrary 获得的 DLL 句柄 </param>
        ///<param name="functionName"> 非托管函数名 </param>
        ///<param name="t"> 对应的委托类型 </param>
        ///<returns> 委托实例，可强制转换为适当的委托类型 </returns>
        public static Delegate GetFunctionAddress(int dllModule, string functionName, Type t)
        {
            int address = GetProcAddress(dllModule, functionName);
            if (address == 0)
                return null;
            else
                return Marshal.GetDelegateForFunctionPointer(new IntPtr(address), t);
        }

        ///<summary>
        /// 将表示函数地址的 intPtr 实例转换成对应的委托
        ///</summary>
        public static Delegate GetDelegateFromIntPtr(IntPtr address, Type t)
        {
            if (address == IntPtr.Zero)
                return null;
            else
                return Marshal.GetDelegateForFunctionPointer(address, t);
        }

        ///<summary>
        /// 将表示函数地址的 int  转换成对应的委托
        ///</summary>
        public static Delegate GetDelegateFromIntPtr(int address, Type t)
        {
            if (address == 0)
                return null;
            else
                return Marshal.GetDelegateForFunctionPointer(new IntPtr(address), t);
        }

        /// <summary>
        /// 加载sdk
        /// </summary>
        /// <param name="lpFileName"></param>
        /// <returns></returns>
        public static int LoadSDK(string lpFileName)
        {
            if (File.Exists(lpFileName))
            {
                var hReservedNull = IntPtr.Zero;
                var dwFlags = LoadLibraryFlags.LOAD_WITH_ALTERED_SEARCH_PATH;

                var result = LoadLibraryEx(lpFileName, hReservedNull, dwFlags);

                var errCode = GetLastError();
                LogHelper.Info($"LoadSDK Result:{result}, ErrorCode: {errCode}");
               
                return result;
            }
            return 0;
        }

        /// <summary>
        /// 释放sdk
        /// </summary>
        /// <param name="handle"></param>
        /// <returns></returns>
        public static int ReleaseSDK(int handle)
        {
            try
            {
                if (handle > 0)
                {
                    LogHelper.Info($"FreeLibrary handle：{handle}");
                    var result = FreeLibrary(handle);
                    var errCode = GetLastError();
                    LogHelper.Info($"FreeLibrary Result:{result}, ErrorCode: {errCode}");
                    return 0;
                }
                return -1;
            }
            catch (Exception ex)
            {
                LogHelper.Error(ex);
                return -1;
            }
        }
    }

    /// <summary>
    /// LoadLibraryFlags
    /// </summary>
    public enum LoadLibraryFlags : uint
    {
        /// <summary>
        /// DONT_RESOLVE_DLL_REFERENCES
        /// </summary>
        DONT_RESOLVE_DLL_REFERENCES = 0x00000001,

        /// <summary>
        /// LOAD_IGNORE_CODE_AUTHZ_LEVEL
        /// </summary>
        LOAD_IGNORE_CODE_AUTHZ_LEVEL = 0x00000010,

        /// <summary>
        /// LOAD_LIBRARY_AS_DATAFILE
        /// </summary>
        LOAD_LIBRARY_AS_DATAFILE = 0x00000002,

        /// <summary>
        /// LOAD_LIBRARY_AS_DATAFILE_EXCLUSIVE
        /// </summary>
        LOAD_LIBRARY_AS_DATAFILE_EXCLUSIVE = 0x00000040,

        /// <summary>
        /// LOAD_LIBRARY_AS_IMAGE_RESOURCE
        /// </summary>
        LOAD_LIBRARY_AS_IMAGE_RESOURCE = 0x00000020,

        /// <summary>
        /// LOAD_LIBRARY_SEARCH_APPLICATION_DIR
        /// </summary>
        LOAD_LIBRARY_SEARCH_APPLICATION_DIR = 0x00000200,

        /// <summary>
        /// LOAD_LIBRARY_SEARCH_DEFAULT_DIRS
        /// </summary>
        LOAD_LIBRARY_SEARCH_DEFAULT_DIRS = 0x00001000,

        /// <summary>
        /// LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR
        /// </summary>
        LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR = 0x00000100,

        /// <summary>
        /// LOAD_LIBRARY_SEARCH_SYSTEM32
        /// </summary>
        LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800,

        /// <summary>
        /// LOAD_LIBRARY_SEARCH_USER_DIRS
        /// </summary>
        LOAD_LIBRARY_SEARCH_USER_DIRS = 0x00000400,

        /// <summary>
        /// LOAD_WITH_ALTERED_SEARCH_PATH
        /// </summary>
        LOAD_WITH_ALTERED_SEARCH_PATH = 0x00000008
    }
}

2. 使用DLLWrapper类动态读取C++Dll，获得函数指针，并且将指针封装成C#中的委托。原因很简单，C#中已经不能使用指针了，如下：

定义委托

UnmanagedFunctionPointer(CallingConvention.StdCall, CharSet = CharSet.Ansi)]
public delegate int Delegate_IKUSBSDK_GetVersion([In] [Out] [MarshalAs(UnmanagedType.LPArray)] byte[] version);

3. 调用函数

//1. 加载sdk
var sdkModule = DLLWrapper.LoadSDK(_route.DeviceA_PATH);

// 2. 通过handle 找到相关的函数
Delegate_IKUSBSDK_GetVersion getVersion = (Delegate_IKUSBSDK_GetVersion)DLLWrapper.GetFunctionAddress(sdkModule, "IKUSBSDK_GetVersion", typeof(Delegate_IKUSBSDK_GetVersion));

var result = getVersion(version);