从C ++调用Win32 DLL [英] Calling Win32 DLL from C++

问题描述

我是新的DLL世界。我已经给了一个Win32 DLL有很多功能。需要从C ++调用这些DLL函数

I am new to the DLL world. I have been given a Win32 DLL which has a lot of functions. Need to call these DLL functions from C++

我想调用 CreateNewScanner ，它创建一个新的扫描器对象，结果在C ++。
DLL中提到的函数是：

I want to call CreateNewScanner which creates a new scanner object and get the results in C++. Function mentioned in the DLL is:

BOOL CreateNewScanner(NewScanner *newScan);

和 NewScanner 是 struct ，如下所示：

// Structure NewScanner is defined in "common.h" .
typedef struct{
  BYTE host_no; // <- host_no =0
  LONG time; // <- command timeout (in seconds)
  BYTE status; // -> Host adapter status
  HANDLE obj; // -> Object handle for the scanner
}NewScanner;

如何调用此函数？从C ++开始，这是我管理的，

How will I call this function? Started with C++ and here is what I managed,

#include <iostream>
#include <windows.h>
using namespace std;
int main(){
  HINSTANCE hInstance;    
  if(!(hInstance=LoadLibrary("WinScanner.dll"))){
      cout << "could not load library" << endl;        
  }
  /* get pointer to the function in the dll*/
  FARPROC handle = GetProcAddress(HMODULE(hInstance), "CreateNewScanner");
  if(!handle){
    // Handle the error
    FreeLibrary(hInstance);
    return "-1";
  }else{    
    // Call the function
    //How to call here??
  }
}

推荐答案

的， return-1是不好的。您将返回一个整数。所以你肯定意味着 return -1 。

First of all, return "-1" is no good. You are expected to return an integer. So you surely mean return -1.

现在回答问题。代替将函数指针声明为 FARPROC ，它更容易声明为函数指针类型。

Now to the question. Instead of declaring the function pointer as FARPROC, it's easier to declare it as a function pointer type.

typedef BOOL (*CreateNewScannerProc)(NewScanner*);

然后调用GetProcAddress如下：

Then call GetProcAddress like this:

HMODULE hlib = LoadLibrary(...);
// LoadLibrary returns HMODULE and not HINSTANCE
// check hlib for NULL

CreateNewScannerProc CreateNewScanner = 
    (CreateNewScannerProc) GetProcAddress(hlib, "CreateNewScanner");
if (CreateNewScanner == NULL)
    // handle error

// now we can call the function
NewScanner newScan;
BOOL retval = CreateNewScanner(&newScan);

说完这些，通常一个库会带有一个头文件应包括它）和用于加载时链接的.lib文件。确保将.lib文件传递给链接器，您只需这样做：

Having said all of that, usually a library will come with a header file (yours clearly does so you should include it) and a .lib file for load-time linking. Make sure that you pass the .lib file to your linker and you can simply do this:

#include "NameOfTheHeaderFileGoesHere.h"
....
NewScanner newScan;
BOOL retval = CreateNewScanner(&newScan);

无需使用 LoadLibrary GetProcAddress 等。

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