DLL Making and Symbols - 2 Queries

My first question, is about DLL creation in C++. I've heard about what DLLs can do for a program, and now I want to implement them in my own programs. I've been thinking of using them first with a simple console-based hello world function, then going onto more advanced functions from this. But regaurdless, do you have any resources that I might be able to look into for coding DLLs in C++? I haven't found any on this board from a search, besides a few questions regaurding errors and the like, but no code was presented in any of these cases, to my dismay. I'de like to take my coding to the next level, and I figure knowing how to code DLLs will get me there.

The second question, has no examples. But it can be simply put: In C++, what are symbols? I've seen this term used frequently in compiler errors, and possibly linker errors, however don't quote me on that. The question popped up in my head while browsing through some CS Mod boards.

Thank you for your time,
~Tronic

Quote:

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The second question, has no examples. But it can be simply put: In C++, what are symbols? I've seen this term used frequently in compiler errors, and possibly linker errors, however don't quote me on that. The question popped up in my head while browsing through some CS Mod boards.

---

In the real world, symbols represent other things. A swatstika for example. In C++, things such as variable name, etc... represent things. These are symbols.

That answers my question about symbols, but what about DLLs? It seems there aren't many that know about them, at least those who browse the C++ threads, haven't gotten a reply in a while.

You might want to do a board search for DLLs and look for a thread started by Rune Hunter. That thread should walk you throug the whole thing.

Thank you Govtcheez :)

and thus, I have come to one more question about DLLs. Very interesting things these are, infact.

Here's my DLL:

dll.h

Code:

---

#include "dll.h"
#include <windows.h>
#include <iostream>
DllClass::DllClass()
{}
DllClass::~DllClass ()
{}
int DllClass::helloWorld()
{
  std::cout << "Hello World!";
  return 0;
} 
BOOL APIENTRY DllMain
(
HINSTANCE hInst   
/* Library instance handle. */ ,
DWORD reason        /* Reason this function is being called. */ ,
LPVOID reserved    /* Not used. */
)
{
    switch (reason)
    {
      case DLL_PROCESS_ATTACH:
        break;
      case DLL_PROCESS_DETACH:
        break;
      case DLL_THREAD_ATTACH:
        break;
      case DLL_THREAD_DETACH:
        break;
    }
    /* Returns TRUE on success, FALSE on failure */
    return TRUE;
}

---

dllmain.cpp

Code:

---

#ifndef _DLL_H_
#define _DLL_H_
#if BUILDING_DLL
# define DLLIMPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */
class DLLIMPORT DllClass
{
  public:
    DllClass();
    virtual ~DllClass(void);
    int helloWorld();
};
#endif /* _DLL_H_ */

---

Here's my program that I want to call the DLL correctly:

main.cpp

Code:

---

#include <stdlib.h>
#include <windows.h>

int main(int argc, char *argv[])
{
  LoadLibrary("dll.dll");
  if(DllClass::helloWorld() = 0)
    std::cout << "\nSuccess!";
  else
    std::cout << "Output failed for some weird reason~!";
  system("PAUSE");       
  return 0;
}

---

It gives me: helloWorld() undeclared (first use this function), and yet helloWorld is in my DLL. I've also tried DllClass::helloWorld(), btw.

Well, there's gonna be a problem with this..

if(DllClass::helloWorld() = 0)

You're trying to assign 0 to DllClass::helloWorld(), not check if helloWorld() returned 0.

Tried that before. It's saying 'Undeclared helloWorld() first use of this function'.

you need to include the header and declare an object of the class.

Code:

---

#include <stdlib.h>
#include <windows.h>
#include "dll.h"
int main(int argc, char *argv[])
{
 DllClass dc;
 dc.helloWorld();
 system("PAUSE");       
 return 0;
}

---

Ahh, that was an..interesting mistake lol. Thanks :)

Only problem I have so far is with the linker..which is interesting.

I've edited my main.cpp code to show the resulting edit. My DLLs code hasn't changed.

The errors it gives me are:

[Linker error] undefined reference to `_imp___ZN8DllClassC1Ev'

[Linker error] undefined reference to `_imp___ZN8DllClass10helloWorldEv'

[Linker error] undefined reference to `DllClass::~DllClass()'

I'm not that good with linkers so...

go to project options and add the library file (with the .a extension) to the linker options.