最近由于工作原因需要封DLL给客户用同时还要提供C#调用demo，这两个好几年都没用过了有点手生，趁热打铁记录一下以供回头查看。
什么？你问我现在在干嘛？哦哦...我在玩儿iOS编程...半路出家自学的那种...好了废话不多说了开干吧(๑•̀ㅂ•́)و✧加油

1.生成"C"的DLL

vs编译器创建win32工程，并创建DLL工程（这里不展示创建，直白点好，直接上代码），然后code
>>> test_dll.h

#ifndef _TEST_DLL_HEADER_H_
#define _TEST_DLL_HEADER_H_

#if defined(TEST_DLL_EXPORT)
#define DLL_API __declspec(dllexport)
#else
#define DLL_API __declspec(dllimport)
#endif

#ifdef __cplusplus
extern "C" {
#endif

    typedef struct {
    
        void(*on_start)(int code, void *param);
        void(*on_stop)(void *param);
    }test_callbacks;

    DLL_API void* create_handle(test_callbacks cb, void *param);
    DLL_API void start_handle(void *handle);
    DLL_API void stop_handle(void *handle);
    DLL_API void destroy_handle(void *handle);

#ifdef __cplusplus
}
#endif

#endif

>>> test_dll.c

///define dll export macro
#define TEST_DLL_EXPORT

#include "test_dll.h"

#include <stdlib.h>
#include <stdio.h>

typedef struct {

    test_callbacks  callbacks;
    void*           callback_param;
}test_handle;

void* create_handle(test_callbacks cb, void *param) {

    test_handle *h = (test_handle*)malloc(sizeof(test_handle));
    if (NULL != h) {

        h->callbacks = cb;
        h->callback_param = param;
    }
    return h;
}


void start_handle(void *handle) {

    test_handle *h = (test_handle*)handle;
    printf(">>> start handle...\n");
    if (NULL != h && NULL != h->callbacks.on_start) {

        h->callbacks.on_start(404, h->callback_param);
    }
}

void stop_handle(void *handle) {

    test_handle *h = (test_handle*)handle;
    printf(">>> stop handle...\n");
    if (NULL != h && NULL != h->callbacks.on_stop) {

        h->callbacks.on_stop(h->callback_param);
    }
}

void destroy_handle(void *handle) {

    test_handle *h = (test_handle*)handle;
    if(NULL != h){

        free(h);
        h = NULL;
    }
}

2.调用DLL演示，在C中调用DLL

>>> use_dll_in_c.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>
#include <strsafe.h>

#include "test_dll.h"

#define API_USE_DLL 1

/// this way need header file
#if !API_USE_DLL
#pragma comment(lib, "dll_for_cs_demo.lib")
#endif


void test_start(int code, void *param) {

    printf(">>> [cb_start] code: %d\nparam: %s\n", code, (char*)param);
}

void test_stop(void *param) {

    printf(">>> [cb_stop] param: %s\n", (char*)param);
}

void PeerLastErrorMessage(PTCHAR function) {

    LPVOID lpMsgBuf;
    LPVOID lpDisplayBuf;
    DWORD dw = GetLastError();
    DWORD len = 0;
    char *str = NULL;

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER |
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        dw,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR)&lpMsgBuf,
        0, NULL);

    // Display the error message and exit the process

    lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT,
        (lstrlen((LPCTSTR)lpMsgBuf) + lstrlen((LPCTSTR)function) + 40) * sizeof(TCHAR));
    StringCchPrintf((LPTSTR)lpDisplayBuf,
        LocalSize(lpDisplayBuf) / sizeof(TCHAR),
        TEXT("%s failed with error %d: %s"),
        function, dw, lpMsgBuf);
#if defined(UNICODE)
    len = WideCharToMultiByte(CP_ACP, 0, (LPCTSTR)lpDisplayBuf, -1, NULL, 0, NULL, 0);
    str = (char*)malloc(sizeof(char) * (len + 1));
    WideCharToMultiByte(CP_ACP, 0, (LPCTSTR)lpDisplayBuf, -1, str, len, NULL, 0);
    str[len] = '\0';
#endif
    //MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK);
    printf("%s\n", str);

    free(str);
    LocalFree(lpMsgBuf);
    LocalFree(lpDisplayBuf);
    //ExitProcess(dw);

}

typedef void* (*_create_h)(test_callbacks cb, void* param);
typedef void(*_all_h)(void* param);

int main(int argc, const char *argv[]) {

    int b = 0;
    void* handle = NULL;
    HMODULE mh = NULL;
    _all_h _handles = NULL;
    _create_h _create = NULL;
    test_callbacks cb = {test_start, test_stop};

#if API_USE_DLL
    /// use dll
    mh = LoadLibrary(L"dll_for_cs_demo.dll");
    if (NULL == mh) {

        PeerLastErrorMessage(L">>> main");
        getchar();
        return EXIT_FAILURE;
    }

    _create_h _ch = (_create_h)GetProcAddress(mh, "create_handle");
    _all_h _sh = (_all_h)GetProcAddress(mh, "start_handle");
    _all_h _eh = (_all_h)GetProcAddress(mh, "stop_handle");
    _all_h _dh = (_all_h)GetProcAddress(mh, "destroy_handle");

    handle = _ch(cb, (void*)"haha");
    _sh(handle);
    _eh(handle);
    _dh(handle);
#else
    /// use lib
    handle = create_handle(cb, (void*)"hehe");
    start_handle(handle);
    stop_handle(handle);
    destroy_handle(handle);
#endif

    printf(">>> press anykey to exit...\n");
    getchar();

    return 0;
}

3.调用DLL演示，在C#中调用DLL

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace use_dll_in_cs
{
    class Program
    {
        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        public delegate void on_start_d(int code, IntPtr param);

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        public delegate void on_stop_d(IntPtr param);

        [StructLayout(LayoutKind.Sequential)]
        public struct callback
        {
            public on_start_d start_cb;
            public on_stop_d stop_cb;
        }

        [DllImport("dll_for_cs_demo.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "create_handle")]
        public extern static IntPtr create_handle(callback cb, IntPtr param);

        [DllImport("dll_for_cs_demo.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "start_handle")]
        public extern static IntPtr start_handle(IntPtr handle);

        [DllImport("dll_for_cs_demo.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "stop_handle")]
        public extern static IntPtr stop_handle(IntPtr handle);

        [DllImport("dll_for_cs_demo.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "destroy_handle")]
        public extern static IntPtr destroy_handle(IntPtr handle);

        public static void test_start_cb(int code, IntPtr param)
        {
            Console.WriteLine(">>> [start_cb]: code: {0}, param: {1}", code, Marshal.PtrToStringAnsi(param));
        }

        public static void test_stop_cb(IntPtr param)
        {
            Console.WriteLine(">>> [stop_cb]: param: {0}", Marshal.PtrToStringAnsi(param));
        }

        static void Main(string[] args)
        {
            callback cb;
            cb.start_cb = test_start_cb;
            cb.stop_cb = test_stop_cb;
            IntPtr str_ptr = Marshal.StringToHGlobalAnsi("hello, c#");
            IntPtr handle = create_handle(cb, str_ptr);
            start_handle(handle);
            stop_handle(handle);
            Console.WriteLine("press any key to exit...");
            Console.ReadLine();

            destroy_handle(handle);
            Marshal.FreeHGlobal(str_ptr);
        }
    }
}