DLL`s

[Crossfire]

OK you will all prob hate me for this "beginner" question...

i have my program in c++, using the Velleman DLL for accessing the PIC on the relay board

HOW do i use a dll in C?

[smokeyangel]

Assuming the DLL doesn't actually need C++ (e.g. can it throw exceptions?) I don't think it's all that different from doing it from C++.

So, there are 2 ways you can load DLLs -- you can do it on explicitly during excution, or implicitly at program startup.

The implicit load at startup way is the simplest, but will only work if the DLL also came with a static library (.lib), and of course a header file. The header file will tell the compiler the definitions it needs, the .lib will keep the linker happy, and the DLL contains the actual code.

Put the DLL in the same directory as your C executable

In MSVC project properties, add the path to the header file to 'additional include directories', the .lib name to Additional Library dependencies (under Linker), put the library path in 'additional library paths'.

You should then be able to call the functions from the DLL just like they were functions declared anywhere else in your project.

If you've managed to end up without a header or .lib, but you know the innards of the DLL or have good documentation, you can explicitly load the DLL.

There's some info about the 2 options here: Linking Implicitly

Do you happen to know what compiler the DLL was built with? There are compatibility issues with VC7 and later MSVCs for some DLLs -- it depends on the characteristics of the DLL. If it's a simple C DLL it should be fine.

[Crossfire]

i only have the dll
this is what i do with c++

#include <iostream>
#include <windows.h>
 

using namespace std;
//----------Set up fuctions from DLL----------//
typedef void(CALLBACK* t_func)(int );
typedef void(CALLBACK* t_func0)();
typedef int(CALLBACK* t_func1)();
typedef void(CALLBACK* t_func2)(int *, int *);
typedef void(CALLBACK* t_func3)(int , int );
typedef int(CALLBACK* t_func4)(int );
typedef bool(CALLBACK* t_func5)(int );
t_func4 OpenDevice;
t_func0 CloseDevice;
t_func0 Version_;
t_func4 ReadAnalogChannel;
t_func2 ReadAllAnalog;
t_func3 OutputAnalogChannel;
t_func3 OutputAllAnalog;
t_func ClearAnalogChannel; 
t_func0 ClearAllAnalog;
t_func SetAnalogChannel; 
t_func0 SetAllAnalog;
t_func WriteAllDigital;
t_func ClearDigitalChannel;
t_func0 ClearAllDigital;
t_func SetDigitalChannel;
t_func0 SetAllDigital;
t_func5 ReadDigitalChannel;
t_func1 ReadAllDigital;
//----------Set up functions for control----------//
int init();
HINSTANCE hDLL;
int foundDLL = 0;

int main()
{
 
 
 int h = init();   
    
 if (!h)
 {
  foundDLL = 1;
 }
 if (foundDLL)
  {
   cout <<"Program Support Files Found"<<endl;
  }
 else
  {
   cout <<"Program Support Files NOT Found"<<endl;
  }
 if (foundDLL == 1)
  {
   OpenDevice(0);
  }
 system("pause");
 if (foundDLL)
  {
   CloseDevice(); 
  }
 FreeLibrary(hDLL);
 return 0;
}
int init()
{
 hDLL = LoadLibrary((LPCWSTR)L"k8055d");
 if (hDLL != NULL)
 {
  OpenDevice = (t_func4) GetProcAddress(hDLL, "OpenDevice");
  if (!OpenDevice)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  CloseDevice = (t_func0) GetProcAddress(hDLL, "CloseDevice");
  if (!CloseDevice)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadAnalogChannel = (t_func4) GetProcAddress(hDLL, "ReadAnalogChannel");
  if (!ReadAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadAllAnalog = (t_func2) GetProcAddress(hDLL, "ReadAllAnalog");
  if (!ReadAllAnalog)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  OutputAnalogChannel = (t_func3) GetProcAddress(hDLL, "OutputAnalogChannel");
  if (!OutputAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  OutputAllAnalog = (t_func3) GetProcAddress(hDLL, "OutputAllAnalog");
  if (!OutputAllAnalog)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearAnalogChannel = (t_func) GetProcAddress(hDLL, "ClearAnalogChannel");
  if (!ClearAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearAllAnalog = (t_func0) GetProcAddress(hDLL, "ClearAllAnalog");
  if (!ClearAllAnalog)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetAnalogChannel = (t_func) GetProcAddress(hDLL, "SetAnalogChannel");
  if (!SetAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetAllAnalog = (t_func0) GetProcAddress(hDLL, "SetAllAnalog");
  if (!SetAllAnalog)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  WriteAllDigital = (t_func) GetProcAddress(hDLL, "WriteAllDigital");
  if (!WriteAllDigital)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearDigitalChannel = (t_func) GetProcAddress(hDLL, "ClearDigitalChannel");
  if (!ClearDigitalChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearAllDigital = (t_func0) GetProcAddress(hDLL, "ClearAllDigital");
  if (!ClearAllDigital)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetDigitalChannel = (t_func) GetProcAddress(hDLL, "SetDigitalChannel");
  if (!SetDigitalChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetAllDigital = (t_func0) GetProcAddress(hDLL, "SetAllDigital");
  if (!SetAllDigital)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadDigitalChannel = (t_func5) GetProcAddress(hDLL, "ReadDigitalChannel");
  if (!ReadDigitalChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadAllDigital = (t_func1) GetProcAddress(hDLL, "ReadAllDigital");
  if (!ReadAllDigital)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  Version_ = (t_func0) GetProcAddress(hDLL, "Version");
  if (!Version_)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  return 0;    // ok
 }       
 return -1;     // error load DLL
}

and this dont work in C

[smokeyangel]

Ah - ok. Yes, this is what I think you need to do in C, too.

It doesn't look too bad: no overloaded functions or anything like that. If you remove the iostream include, namespace use, and turn the couts into printfs that'll take care of most of it.

One of the function prototypes returns a bool. According to Fundamental Types (C++), bool is 1 byte in all recent versions of MSVC - so you should be able to use a 'char' here safely for now (portability hazard but in a file full of Windows DLL handling functions - think the portability gods can look the other way)

[ledow]

Yeah, pretty much identical code, just run it through a C compiler and fix the errors/warnings that are generated for all the C++-isms.

What "doesn't work" about it? Doesn't compile? Doesn't link? Doesn't open the DLL on execution? Doesn't find the named functions inside the DLL (there's possibly something called name-mangling interfering but I'd think it's very unlikely for this example with a manufacturer-supplied DLL)?

Each of those is a different problem.

[Crossfire]

compiling prob creating dlltest.obj

int init(void)
{
 hDLL = LoadLibrary((LPCWSTR)L"k8055d");
 if (hDLL != NULL)
 {

dlltest.c(77): error #2140: Type error in argument 1 to 'function'; expected 'const char *' but found 'const wchar_t *'.

error was on the following line

hDLL = LoadLibrary((LPCWSTR)L"k8055d");

[iMalc]

That means that you need to change your project settings from multi-byte to Unicode.
The code you have above is fine for both C and C++.

[Crossfire]

changed

hDLL = LoadLibrary((LPCWSTR)L"k8055d.dll");

to

hDLL = LoadLibrary((LPCSTR)L"k8055d.dll");

and got

POLINK: error: Unresolved external symbol '_WinMain@16'.
POLINK: fatal error: 1 unresolved external(s).

[Crossfire]

ok using

 
 
#include<stdio.h>
#include<windows.h>
 

//----------Set up fuctions from DLL----------//
typedef void(CALLBACK* t_func)(int );
typedef void(CALLBACK* t_func0)();
typedef int(CALLBACK* t_func1)();
typedef void(CALLBACK* t_func2)(int *, int *);
typedef void(CALLBACK* t_func3)(int , int );
typedef int(CALLBACK* t_func4)(int );
typedef char(CALLBACK* t_func5)(int );
t_func4 OpenDevice;
t_func0 CloseDevice;
t_func0 Version_;
t_func4 ReadAnalogChannel;
t_func2 ReadAllAnalog;
t_func3 OutputAnalogChannel;
t_func3 OutputAllAnalog;
t_func ClearAnalogChannel; 
t_func0 ClearAllAnalog;
t_func SetAnalogChannel; 
t_func0 SetAllAnalog;
t_func WriteAllDigital;
t_func ClearDigitalChannel;
t_func0 ClearAllDigital;
t_func SetDigitalChannel;
t_func0 SetAllDigital;
t_func5 ReadDigitalChannel;
t_func1 ReadAllDigital;
//----------Set up functions for control----------//
int init(void);
HINSTANCE hDLL;
int foundDLL = 0;

int main(void)
{
 
 
 int h = init();   
    
 if (!h)
 {
  foundDLL = 1;
 }
 if (foundDLL)
  {
   printf("Program Support Files Found\n");
  }
 else
  {
   printf("Program Support Files NOT Found\n");
  }
 if (foundDLL == 1)
  {
   OpenDevice(0);
  }
 system("pause");
 if (foundDLL)
  {
   CloseDevice(); 
  }
 FreeLibrary(hDLL);
 return 0;
}
int init(void)
{
 hDLL = LoadLibrary((LPCSTR)L"k8055d.dll");
 if (hDLL != NULL)
 {
  OpenDevice = (t_func4) GetProcAddress(hDLL, "OpenDevice");
  if (!OpenDevice)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  CloseDevice = (t_func0) GetProcAddress(hDLL, "CloseDevice");
  if (!CloseDevice)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadAnalogChannel = (t_func4) GetProcAddress(hDLL, "ReadAnalogChannel");
  if (!ReadAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadAllAnalog = (t_func2) GetProcAddress(hDLL, "ReadAllAnalog");
  if (!ReadAllAnalog)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  OutputAnalogChannel = (t_func3) GetProcAddress(hDLL, "OutputAnalogChannel");
  if (!OutputAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  OutputAllAnalog = (t_func3) GetProcAddress(hDLL, "OutputAllAnalog");
  if (!OutputAllAnalog)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearAnalogChannel = (t_func) GetProcAddress(hDLL, "ClearAnalogChannel");
  if (!ClearAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearAllAnalog = (t_func0) GetProcAddress(hDLL, "ClearAllAnalog");
  if (!ClearAllAnalog)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetAnalogChannel = (t_func) GetProcAddress(hDLL, "SetAnalogChannel");
  if (!SetAnalogChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetAllAnalog = (t_func0) GetProcAddress(hDLL, "SetAllAnalog");
  if (!SetAllAnalog)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  WriteAllDigital = (t_func) GetProcAddress(hDLL, "WriteAllDigital");
  if (!WriteAllDigital)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearDigitalChannel = (t_func) GetProcAddress(hDLL, "ClearDigitalChannel");
  if (!ClearDigitalChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ClearAllDigital = (t_func0) GetProcAddress(hDLL, "ClearAllDigital");
  if (!ClearAllDigital)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetDigitalChannel = (t_func) GetProcAddress(hDLL, "SetDigitalChannel");
  if (!SetDigitalChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  SetAllDigital = (t_func0) GetProcAddress(hDLL, "SetAllDigital");
  if (!SetAllDigital)  
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadDigitalChannel = (t_func5) GetProcAddress(hDLL, "ReadDigitalChannel");
  if (!ReadDigitalChannel)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  ReadAllDigital = (t_func1) GetProcAddress(hDLL, "ReadAllDigital");
  if (!ReadAllDigital)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  Version_ = (t_func0) GetProcAddress(hDLL, "Version");
  if (!Version_)
  {      // handle the error
   FreeLibrary(hDLL); 
   return -2;
  }
  return 0;    // ok
 }       
 return -1;     // error load DLL
}

now it compiles, but displays

"Program Support Files NOT Found"

so does not seem to be loading the dll, that is in the same folder as the project.

thoughts?

oh and once in a while when i build the same thing, no errors or warnings, and sometimes i get
"dlltest.c(47): warning #2203: Function 'main' can't be __stdcall, changed to __cdecl."

[Crossfire]

i have found alot on loading dll`s. Mostly it is from the header and lib files, which i do not have. Evrything else seems to be in C++.

i am totally lost here, and searching the net, searching my books (the things before ebooks!!) and of course all my ebooks....

i know someone has to have loaded dll`s in C before....

[stahta01]

I guessed by doing this with MinGW GCC C Compiler.

And it appeared to work with the DLL is the same folder as the EXE.

hDLL = LoadLibrary("k8055d.dll");

[Crossfire]

SON OF A...... out of everything i tried, _T, Text, (LPCSTR),(STR),(LPCWSTR)....The one thing i didnt try, and it worked!!!!

Stahta, You been great since i joined this board!!! I owe you a couple now, and of course, everyone else too!!!