Windows Programming: Creating/Using DLL’s
In the world of programming, there are MANY different types. Unfortunately, programming for some systems is different than others, but it’s things like that which keep the world turning. Today, we will discuss what exactly is a Dynamic Link Library (DLL) and how to use them to keep our programming easier and more organized. I will also include an Italian translation of this tutorial in the download source below! (Un traduzione del questo tutorial è in il download link per richiesta)
We’ll begin with what a DLL is and what it’s purpose is. A DLL is a wonderful tool to keep your programs organized by creating a DLL per set of functions. Also, it helps developers keep their closed source functions closed source, but also allows (with proper documentation/instructions on doing so) other users to use their work. Below we will give a few simple examples on how it all works!
To create the DLL we will be using Microsoft’s Visual C++. This is a free IDE compiler. I use it for any sort of Windows programming that I may do and will include the solution file in the download. Of course, I prefer GNU’s GCC which is also free, but the Windows ports of the compiler are not as good as the standard linux version.
The first note that I want to make is that if you’re making this project on your own (and not using my solution file), be sure to go to Project->Your Project’s Properties->Configuration Properties->General->Configuration Type and change it to “Dynamic Library (.dll)” otherwise it will not compile correctly.
Now in this tutorial, I am assuming you already know how to write programs, so this first file is test_dll.cpp. It contains the actual definitions, etc. of our functions:
/**
* Test Dynamic Library File
*
* (C) 2009 Dennis J. McWherter, Jr. All Rights Reserved.
*
*/#define WIN32_LEAN_AND_MEAN // No need for the extra stuff.
// Non includere i file cui non hanno un scopo
#include <windows.h>
#include <iostream>
#include "test_dll.h" // Our header file
// Il nostro header fileusing namespace std;
// Initiate the DLL (For programs)
// Iniziare il DLL (per i programmi)
BOOL APIENTRY DllMain(HINSTANCE dllHinst, DWORD reason, LPVOID lpvReserved){
// Use a switch to tell the program how to cycle the processes
// Usare un switch per fare il programma funziona
switch(reason){
case DLL_PROCESS_ATTACH:
break;
case DLL_PROCESS_DETACH:
break;
case DLL_THREAD_ATTACH:
break;
case DLL_THREAD_DETACH:
break;
}
return true;
}// The functions of our class. These are defined in "test_dll.h"
// Le funzioni del nostro class. Gli questi sono definire in "test_dll.h"// Constructor
test_dll::test_dll(){}// Basically a pointless function just to see how we can make them work together XD
// Una funziona senza la usa. è più di un demonstrazione.
char test_dll::func1(char lang){
return lang;
}int test_dll::func2(float x,float y,char op){
// Simple math function!
// Semplice funziona della matematica
switch(op){
case 'a':
cout<< x << "+" << y << "=" << x+y;
return 0;
break;
case 's':
cout<< x << "-" << y << "=" << x-y;
return 0;
break;
case 'd':
cout<< x << "/" << y << "=" << x/y;
return 0;
break;
default:
cout<< x << "*" << y << "=" << x*y;
return 0;
break;
}
return 0;
}
Again, a fairly straightforward example. What you do have to notice in this that is different from most programs is that fact that we’re not really calling a “Main” function to be run. We call BOOL WINAPI DllMain instead. This next file is the header file. A rather important file overall as it let’s us know what to export.
/**
* Test Dynamic Library File
*
* (C) 2009 Dennis J. McWherter, Jr. All Rights Reserved.
*
*/#ifndef HEADER
#define HEADER
// To keep the code clean we'll define this with a macro but this tells the processor
// to export whichever function/class it preceeds.
// Ci definiamo il questo con un macro ma ci vedremmo come lo funziona in più ritardo
#define EXPORT_DLL __declspec(dllexport)// Now our class - If you export a class, all its functions come with!
else do each function
// Adesso il nostro class! Se exporti un class poi i tutti funzione di lo sono exportare.
// se individuale ti exporti poi si deve __declspec(dllexport) per ogni
class EXPORT_DLL test_dll{ // = class __declspec(dllexport) test_dll{
public:
test_dll(); // Constructor/Costruttore
char func1(char lang); // First function definition/La definizione della prima funziona
int func2(float x,float y,char op);
};#endif
The comments explain it, but it’s really worth going over again. EXPORT_DLL is defined just for the purpose that we could potentially have more than a single class to export. This goes both ways for the dllexport and dllimport options, so really, EXPORT_DLL just translates to __declspec(dllexport) which would also work if you replaced EXPORT_DLL. Now, compile that code and VC++ should provide you with a .dll file and a .lib file with whatever name you gave the project (in our case: “DLL_Tutorial.lib/.dll”).
Now, you cannot run DLL files by themselves; you need a client program (.exe) which is what we’re getting to now. For the sake of brevity, we will just make this a simple console program which runs the proper functions. Now, create a new project and make sure you copy the “DLL_Tutorial.lib” file into the source directory. You need the .lib file to compile the client program, but you only need the .dll to run the program.
So here is the client main file. A console program of course to keep things simple We’ll call this test_client.cpp
/**
* Test Dynamic Library File
*
* (C) 2009 Dennis J. McWherter, Jr. All Rights Reserved.
*
*/#include <iostream>
#include <string>
#include "test_client.h"using namespace std;
int main(){
// Create object to class
// Creare l'oggetto a class
test_dll test;// Init var
string num1,num2,addition,subtraction,division,multiplication,ans,operation;
float x,y;
char choice[5], op[5]; // Allow more chars just in case - otherwise we'll break the script
// Permettere dei più caratteri così non ci romperiamo il script!
cout<< "Please select a language\r\n\r\nEnglish - en\r\nItaliano - it\r\n \r\nSelect: ";
cin>>choice;
switch(test.func1(choice[0])){
case 'i':
num1 = "Numero 1: ";
num2 = "Numero 2: ";
addition = "Per piacere selezi i tuoi numeri per aggiungiere";
subtraction = "Per piacere selezi i tuoi numeri per sottrarre";
division = "Per piacere selezi i tuoi numeri per dividere";
multiplication = "Per piacere selezi i tuoi numeri per moltiplicare";
ans = "La tua risposta: ";
operation = "\r\nPer piacere selezi il tuo operazione:\r\na - Aggiungiere\r\ns - Sottrarre\r\nd - Divisione\r\nm - Moltiplicazione\r\n\r\nSelection: ";
break;
default:
num1 = "Number 1: ";
num2 = "Number 2: ";
addition = "Please select your numbers to add";
subtraction = "Please select your numbers to subtract";
division = "Please select your numbers to divide";
multiplication = "Please select your numbers to multiply";
ans = "Your answer: ";
operation = "\r\nPlease select your option:\r\na - Addition\r\ns - subtraction\r\nd - Division\r\nm - Multiplication\r\n\r\nSelection: ";
break;
}cout<< operation;
cin>>op;
cout<< endl << endl << num1;
cin>>x;
cout<< endl << num2;
cin>>y;test.func2(x,y,op[0]);
cout<< endl << endl << "Type in anything to exit...";
cin>>op;return 0;
}
Naturally, the header file that follows is test_client.h
/**
* Test Dynamic Library File
*
* (C) 2009 Dennis J. McWherter, Jr. All Rights Reserved.
*
*/#ifndef TEST_HEADER
#define TEST_HEADER
#define DLL_IMPORT __declspec(dllimport) // Same concept as export
// Il stesso concepto come export// Define the class
// What is the purpose of redefining? That's all you need to do is redefine structure
// and not function
// Perchè ti deve ridefinire la class? Perché solo lo struttura si deve essere definire!
// e no funziona
class DLL_IMPORT test_dll{
public:
test_dll(); // Constructor/Costruttore
char func1(char lang); // First function definition/La definizione della prima funziona
int func2(float x,float y,char op);
};#endif
Within these two files, they are essentially creating a calculator. Since I wrote this program in dual languages, I added SIMPLE (meaning hard-coded) dual language support into the program. Also, this gives a reason for the first function, just to see how one can use multiple functions from a DLL just as if they were in the source.
If anyone has further questions or is receiving errors, feel free to let me know and I will be glad to help! Now make sure, however, that everything is set right as well. I ran into an error compiling the client the first time because my project subsystem (found in project properties->linker->System) was set to WINDOWS rather than CONSOLE so it was looking for the WINMAIN where there was none. So just a word of caution to anyone trying this without my source and you are receiving a WINMAIN compilation error.
So the land of DLL’s really aren’t as complex as it seems. It’s simply a closed source utility which helps other developers in WINDOWS programs.
Regards,
Dennis M.