函数指针作为函数参数的用法总结及其意义--首次前向调用

例：

有个socketclient.dll，用dependency walker可以查看到dll的方法。

 

第一步 Load DLL

HINSTANCE hInstance;

    string pathStr= "socketclient.dll";

    LPCSTR sss = pathStr.c_str();

    hInstance =LoadLibrary("socketclient.dll");

    if (hInstance == NULL)

    {

         printf("LoadLibrary() 失败");

         return 0;

    }

在这里注意编码的问题。

右键属性如下图：

 

将字符集修改为使用多字节字符集。

如果使用Unicode字符集则需要做修改，Unicode时，LoadLibrary的参数是LPCWSTR。所以需要做转化。

LPCWSTR stringToLPCWSTR(string orig)

{

    size_t origsize = orig.length() + 1;

    const size_t newsize = 100;

    size_t convertedChars = 0;

    wchar_t *wcstring = (wchar_t *)malloc(sizeof(wchar_t)*(orig.length() - 1));

    mbstowcs_s(&convertedChars, wcstring, origsize, orig.c_str(), _TRUNCATE);

 

    return wcstring;

}

int main()

{

    HINSTANCE hInstance;

    string pathStr= "socketclient.dll";

    LPCTSTR sss = stringToLPCWSTR(pathStr);

    hInstance =LoadLibrary(sss);

    if (hInstance == NULL)

    {

         printf("LoadLibrary() 失败");

         return 0;

    }

}

第二步 声明函数指针类型

//客户端初始化 获取handle上下

//声明一个函数指针类型

typedef int(*CltSocketInit)(void **handle /*out*/);

 

//客户端发报文

typedef int(*CltSocketSend)(void *handle /*in*/, unsigned char *buf /*in*/, int buflen /*in*/);

 

 

//客户端收报文

typedef int(*CltSocketRev)(void *handle /*in*/, unsigned char *buf /*in*/, int *buflen /*in out*/);

 

//客户端释放资源

typedef int(*CltSocketDestory)(void *handle/*in*/);

第三步 实现函数的调用。

CltSocketInit cltSocketInit = (CltSocketInit)::GetProcAddress(hInstance, "cltSocketInit");

    if (cltSocketInit == NULL)

    {

         return 0;

    }

    CltSocketSend cltSocketSend = (CltSocketSend)::GetProcAddress(hInstance, "cltSocketSend");

    CltSocketRev cltSocketRev = (CltSocketRev)::GetProcAddress(hInstance, "cltSocketRev");

    CltSocketDestory cltSocketDestory = (CltSocketDestory)::GetProcAddress(hInstance, "cltSocketDestory");

 

 

    //执行动态库函数调用

    unsigned char buf[128];

    int buflen = 128;

 

    unsigned char outbuf[4096];

    int outbuflen = 4096;

 

    strcpy((char *)buf, "aaaaaaaaaafffffffffdddddd");

    buflen = 9;

 

    void *handle = NULL;

    int ret = 0;

    ret = cltSocketInit(&handle);

    ret = cltSocketSend(handle, buf, buflen);

    ret = cltSocketRev(handle, outbuf, &outbuflen);

    ret = cltSocketDestory(handle);

    if (memcmp(buf, outbuf, outbuflen) == 0)

    {

         printf("发送数据和接受的数据一样 ok\n");

    }

    else

    {

         printf("发送数据和接受的数据不一样\n");

    }

完整代码如下：

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

#include <windows.h>

#include <iostream>

using namespace std;

 

//客户端初始化 获取handle上下

//声明一个函数指针类型

typedef int(*CltSocketInit)(void **handle /*out*/);

 

//客户端发报文

typedef int(*CltSocketSend)(void *handle /*in*/, unsigned char *buf /*in*/, int buflen /*in*/);

 

 

//客户端收报文

typedef int(*CltSocketRev)(void *handle /*in*/, unsigned char *buf /*in*/, int *buflen /*in out*/);

 

//客户端释放资源

typedef int(*CltSocketDestory)(void *handle/*in*/);

 

LPCWSTR stringToLPCWSTR(string orig)

{

    size_t origsize = orig.length() + 1;

    const size_t newsize = 100;

    size_t convertedChars = 0;

    wchar_t *wcstring = (wchar_t *)malloc(sizeof(wchar_t)*(orig.length() - 1));

    mbstowcs_s(&convertedChars, wcstring, origsize, orig.c_str(), _TRUNCATE);

 

    return wcstring;

}

int main()

{

    HINSTANCE hInstance;

    string pathStr= "socketclient.dll";

    LPCTSTR sss = stringToLPCWSTR(pathStr);

    hInstance =LoadLibrary(sss);

    if (hInstance == NULL)

    {

         printf("LoadLibrary() 失败");

         return 0;

    }

    CltSocketInit cltSocketInit = (CltSocketInit)::GetProcAddress(hInstance, "cltSocketInit");

    if (cltSocketInit == NULL)

    {

         return 0;

    }

 

    CltSocketSend cltSocketSend = (CltSocketSend)::GetProcAddress(hInstance, "cltSocketSend");

    CltSocketRev cltSocketRev = (CltSocketRev)::GetProcAddress(hInstance, "cltSocketRev");

    CltSocketDestory cltSocketDestory = (CltSocketDestory)::GetProcAddress(hInstance, "cltSocketDestory");

 

 

    //执行动态库函数调用

    unsigned char buf[128];

    int buflen = 128;

 

    unsigned char outbuf[4096];

    int outbuflen = 4096;

 

    strcpy((char *)buf, "aaaaaaaaaafffffffffdddddd");

    buflen = 9;

 

    void *handle = NULL;

    int ret = 0;

    ret = cltSocketInit(&handle);

    ret = cltSocketSend(handle, buf, buflen);

    ret = cltSocketRev(handle, outbuf, &outbuflen);

    ret = cltSocketDestory(handle);

    if (memcmp(buf, outbuf, outbuflen) == 0)

    {

         printf("发送数据和接受的数据一样 ok\n");

    }

    else

    {

         printf("发送数据和接受的数据不一样\n");

    }

    return 0;

}

运行结果：