Lab windows dll

[sathiyamurthy]

HI all,
i have created a dll using Labwindows ..... can anyone suggest me how to use that dll in vc++ ?

with regards
sathya

[weaknessforcats]

You:

1) call LoadLibrary to load the dll.
2) call GetProcAddress to obtain the address of the function to call. This will be returned as a FARPROC.
3) Use reinterpret_cast<> () to type cast the FARPROC to a function pointer having the correct arguments and return type
4) call the function using the function pointer
5) call FreeLibrary when you are finished with the dll

Note:
A dll is a relic from the C age. That means no functtion overloading and that means no name mangling on the C++ side. The C++ functions must be extern "C" or the dll must have been built using a DEF file containing the export names of the mangled C++ function names.

Example:

 
int main()
{
    cout << "Calling functions from a dll" << endl;
 
    //First, load the dll into memory
   HMODULE theDll =   LoadLibrary "C:\\Scratch\\ClassDemos\\ADll\\Debug\\ADll.dll");
   if (!theDll)
   {
      cout << "The dll failed to load" << endl;
      return 1;
   }
 
   //Second, get the address of the desried function from the dll
   FARPROC addr = GetProcAddress(theDll, "DisplayFromDll");
   if (!addr)
   {
      //Look up the error in the system errors list
      unsigned int what = GetLastError();
      if (what == ERROR_PROC_NOT_FOUND)
      {
          cout << "Function not found in the dll" << endl;
      }
      else
      {
        cout << "Error: " << what << endl;
      }
     return 2;
   }
    cout << "The function has been located in the dll" << endl;
   //Declare a function pointer that can accept the address of the function.
   //You will need to know the function prototype to do this.
   //Dll function prototypes should be provided by the vendor of the dll
   void (__stdcall *DisplayFromDll)();
   //Type-cast the address returned from GetProcAddress to the function pointer type
   DisplayFromDll = reinterpret_cast<void (__stdcall *)()>  (addr);
   //Now use the function pointer to call the function:
    DisplayFromDll();
 
   //If you don't use a .def file in the dll, you must use the mangled name
   //Second, get the address of the desried function from the dll
   addr = GetProcAddress(theDll, "AreaOfSquare");
   if (!addr)
   {
      //Look up the error in the system errors list
     unsigned int what = GetLastError();
     if (what == ERROR_PROC_NOT_FOUND)
      {
         cout << "Function not found in the dll" << endl;
      }
     else
     {
          cout << "Error: " << what << endl;
     }
     return 2;
   }
 
    cout << "The function has been located in the dll" << endl;
    //Declare a function pointer that can accept the address of the function.
    //You will need to know the function prototype to do this.
    //Dll function prototypes should be provided by the vendor of the dll
    int (__stdcall *AreaOfSquare)(int, int);
    //Type-cast the address returned from GetProcAddress to the function pointer type
   AreaOfSquare = reinterpret_cast<int (__stdcall*)(int,int)>  (addr);
   //Now use the function pointer to call the function:
    cout << "The area of a 6x8 square is " << AreaOfSquare(6,8) << endl;;
 
   //Finally, unload the dll from memory
   FreeLibrary(theDll);
 
   return 0;
}
 

The dll code:

 
#include <iostream>
using namespace std;
 
void __stdcall DisplayFromDll()
{
    cout << "This function was called from ADLL.dll" << endl;
}
 
int __stdcall AreaOfSquare (int len, int wid)
{
    return len * wid;
}
 

and the dll DEF file:

;BEGIN ADLL.DEF FILE
;This DEF file is required becuase the argument to GetProcAddress()
;for the function is a C-string and it will never be equal to the
;C++ mangled name for the function
;This DEF file maps the mangled name to a name that can be used with GetProcAddress()
;Note also: Change project settings in Visual Studio to send the LINK this def file.
;Visual Studio.NET: Project Properties/Linker/Input/Module Definition File/...Path to the def file\Adll.def
LIBRARY ADll 
EXPORTS 
;Exported Name    C++ Mangled Name
AreaOfSquare   =  ?AreaOfSquare@@YGHHH@Z
DisplayFromDll =  ?DisplayFromDll@@YGXXZ
;END DEF FILE 
 

[sathiyamurthy]

thanks for ur help ...