C++ compiler(G++) comes up with error when I try to compile a program using Qt.

rohedin · 05-26-2010, 12:01 PM

I am using the C++ compiler G++ to compile my programs on Linux Mint 8 - Gnome. I recently installed QT and when I tried to compile a simple "Hello World!" program it gave me this error:

Quote:

mint@mint ~ $ g++ HelloWorldQt.cpp -I /usr/include/qt4/ -o HelloWorld!
/tmp/cc1oEaHl.o: In function `main':
HelloWorldQt.cpp: (.text+0x2a): undefined reference to `QApplication::QApplication(int&, char**, int)'
HelloWorldQt.cpp: (.text+0x53): undefined reference to `QPushButton::QPushButton(QString const&, QWidget*)'
HelloWorldQt.cpp: (.text+0xa1): undefined reference to `QApplication::exec()'
HelloWorldQt.cpp: (.text+0xaf): undefined reference to `QPushButton::~QPushButton()'
HelloWorldQt.cpp: (.text+0xc2): undefined reference to `QPushButton::~QPushButton()'
HelloWorldQt.cpp: (.text+0xd6): undefined reference to `QApplication::~QApplication()'
HelloWorldQt.cpp: (.text+0xf2): undefined reference to `QApplication::~QApplication()'
/tmp/cc1oEaHl.o: In function `QString::QString(char const*)':
HelloWorldQt.cpp: (.text._ZN7QStringC1EPKc[QString::QString(char const*)]+0x1d): undefined reference to `QString::fromAscii_helper(char const*, int)'
/tmp/cc1oEaHl.o: In function `QString::~QString()':
HelloWorldQt.cpp: (.text._ZN7QStringD1Ev[QString::~QString()]+0x2d): undefined reference to `QString::free(QString:

ata*)'
/tmp/cc1oEaHl.o: In function `QWidget::resize(int, int)':
HelloWorldQt.cpp: (.text._ZN7QWidget6resizeEii[QWidget::resize(int, int)]+0x35): undefined reference to `QWidget::resize(QSize const&)'
collect2: ld returned 1 exit status
mint@mint ~ $

This is the code in HelloWorldQt.cpp:

Code:

#include <QtGui/QApplication>
#include <QtGui/QPushButton>

int main(int argc, char *argv[])
{
	QApplication app(argc, argv);

	QPushButton hello("Hello world!");
	hello.resize(100, 30);

	hello.show();
	return app.exec();
}

I have tried using GTK instead but I get a similar error.
If anyone knows why this is happening or how to fix it, your help would be greatly appreciated. Thanx!

Nylex · 05-26-2010, 12:16 PM

Those seem to be linker errors. Why don't you just use qmake to generate a makefile and then run make to build the program (this might not be the correct sequence of commands, because I can't remember). See the Qt documentation..

smeezekitty · 05-26-2010, 12:21 PM

Try adding -lgtk to the end of the command line.

graemef · 05-26-2010, 09:14 PM

As Nylex suggested you need to use qmake. The documentation is quite good and qmake is fairly easy to learn.

Nylex · 05-26-2010, 11:37 PM

Quote:

Originally Posted by smeezekitty

Try adding -lgtk to the end of the command line.

Again, for GTK read the documentation: http://library.gnome.org/devel/gtk-t...able/x111.html

mac.tieu · 05-26-2010, 11:57 PM

You should create a HelloWorldQt.pro in source directory like this:

Code:

TARGET = HelloWorldQt
TEMPLATE = app
SOURCES += HelloWorldQt.cpp

Run qmake to create Makefile

Code:

qmake

make to create target application

Code:

make

MT

Nylex · 05-27-2010, 12:59 AM

I think if you run "qmake -project" it generates the project file for you.

rohedin · 05-27-2010, 10:28 AM

Thank you so much, everyone who posted a response!

Especially mac.tieu for your clear and helpful instructions!
With your help I got my first QT program to compile and run successfully. I hope this post is useful to other people who might have the same problem

Thanx and Bye!