Development of Applications of Cross-Platform with Qt and MSVC++ - Part 1

Introduction

With this article, I intend to begin a series of articles on multi-platform development of software using C++ as the language and the framework Qt.

I have been developing software for a few year and I always try to maintain my programs. This is not an easy task, because to accomplish this task, it is necessary to define which operating systems will be accepted.

I usually work with a simpler group of systems (Windows, Linux and Palm OS), therefore the task that seems easy it is actually arduous.

In this article, I will present the tools used to develop programs carried using the Qt library. I won't flee the rule of the "Hello world!" (the apple for the designers).

First Program

I will give the example of the traditional "Hello World" so that one can have a fast idea of the library and also the traditional program for console.

//CODE: hello.cpp  
#include <qapplication.h> //QApplication  
#include <qlabel.h> / / QLabel  
  
int main(int argc, char * argv [])  
{  
   / / create the application object and initialize it.  
        QApplication app(argc, argv);  
   / / create the main object/widget required to receive message   
        QLabel * lbl = new QLabel ("Hello World! ", 0);  
   / / it defines the main object/widget  
        app.setMainWidget(lbl);  
   / / we need show it (required)  
        lbl->show ();  
   / / event loop (required)  
        return app.exec ();  
}    

However to compile this code, we need a makefile to build the executable easily. If you are using Qt-3.x or more recent version, you can use the automatic generator that accompanies your own Qt.

I want to make it clear that the previous code can run in three different operating systems with ZERO alteration. You should just compile the code with the appropriate compiler for the wanted operating system. (Win=MSVC++; Linux=GCC; MacOS=CodeWarrior).

In the DOS prompt, you should execute the following commands in the exact same order:

qmake - project - hello.pro  
qmake  
nmake    

The first command will join all of the file sources in the current folder and create a project file. The second command will create the necessary makefile for the construction of the executable. You can call CL.EXE directly, but it is faster to use the generator of Qt. See the content of the project file below generated by qmake:

######################################################################  
# Automatically generated by qmake (1.06c) sáb 4. jun 18:50:03 2005  
###################################################################### TEMPLATE = app  
CONFIG -= moc  
INCLUDEPATH += .  
# Input  
SOURCES += Hello.cpp  

The classic helloworld from Microsoft DOS is:

#include <stdio.h>

int main(int argc, char *argv[])
{
    printf("Hello world!\n");    
}

If you are using Microsoft Windows, then you will have the file hello.exe that can be run by double clicking of the mouse or through the prompt of Microsoft-DOS. If the used system goes Linux, it will be enough to turn through prompt ./hello or through double click in the manager of Windows in use.

If you are using MAC OS, I recommend you ask somebody, a person who knows the system (this is not me.... I have never used it).

The components of Qt will accept text HTML, therefore you will be surprised when changing "Hello World! " for something of the type "<H1> Hello World! </ H1>. This will work. But you can change the label for other control / widget. See the change below for a button.

//CODE: hello.cpp  
#include <qapplication.h> //QApplication  
#include <qpushbutton.h> / / QPushButton
  
int main(int argc, char * argv [])  
{  
   // create the application object and initialize it.  
        QApplication app(argc, argv);  
   // create the main object/widget required to receive message   
        QPushButton * btn = new QPushButton("Hello World  and Quit! ", 0);  

  //new code to close on button click ;-)

  //We should connect the event Click () to the command Quit () of the application.    

    QObject::connect(btn, SIGNAL(clicked()), &app, SLOT(quit());

   // it defines the main object/widget  
        app.setMainWidget(btn);  
   // we need show it (required)  
        btn->show ();  
   // event loop (required)  
        return app.exec ();  
} 

You must have noticed in the previous code that the commands SLOT() and SIGNAL() are macros that will be explained later.

I am writing this small article to show the 1-2-3 of Qt. There is an IDE that allow us to draw the screens (AppWizard) and to connect the events visually, and soon we can write functional code. This will be the subject of the next article.

I will see you soon!

History

• 4^th June, 2005: Initial post