Qt-interest Archive, December 2006
Porting from Qt 2 to 4
Message 1 in thread
Porting from Qt 2 to 4
======================
This is a little guide how to port from Qt2 to 4. In detail it was "Qt
2.1.0-beta2" to "Qt 4.2.2".
The project I used for this test has about 35 own classes and about 50
files. Note: The project I used did not used any GUI files like ".ui"
files from the QDesigner.
Note: It seems to be that Unix/Linux is much more fault tolerance then
Windows Systems. You can have memory leeks on a Unix/Linux box and it
works, but not on Windows (Crashes, Bluescreen on Windows < NT/XP).
0. Do backup first. (Source and EXE/DLLs etc.!)
It is important, so you can look how the "original" should work.
1. Read the "Porting to Qt 4" guide from Trolltech at
http://doc.trolltech.com/4.2/porting4.html
2. Used "qt3to4.exe" for automatically change some names.
See generated "portinglog.txt" for details, what is changed.
3. Create a new ".pro" file with "qmake -project".
new.pro:
--------
...
QT += qt3support
TEMPLATE = app
LANGUAGE = C++
CONFIG += console
.......
------
The console in CONFIG is needed for debugging like QDebug and console
print outs with cout << "Some error" and things like that. Sometimes
very helpfull.
4. Then, try to compile with
qmake
make release // or whatever you need, also make debug etc.
5. Error. Do some changes.
Maybe you have to change the occurency where you source code appears in
the .pro file. Idea: compile easy things first, then the difficult
things. So, move arround your source, that it compiles things you know
it may work first. -- If something does not work after a minute, take an
other file.
Take also a look in the old docu from Trolltech. It can be very
important to understand, how things worked in history.
The oldest is Qt2.3 http://doc.trolltech.com/2.3/index.html
But note: Our very old code uses Qt2.1.0-beta2 from the year 2000(!).
Namespaces
==========
Maybe you have to use
std::cout << "myFunc(): Start..." << std::endl;
indead of:
cout << "myFunc(): Start..." << endl;
Or
using namespace std;
at the beginning of the file.
Old: AlignCenter, Key_Escape, etc.
New: Qt::AlignCenter, Qt::Key_Escape, etc.
QMouseEvent* event;
Old: if(event->button()==Qt::LeftButton) {
New: if(event->button()==QMouseEvent::LeftButton) {
In myglobal.h or things like that:
----------------------------------
Old:
* error: `cout' undeclared (first use this function)
* ... warning: #warning This file includes at least one deprecated or
antiquated header. Please consider using one of the 32 headers found in
section 17.4.1.2 of the C++ standard. Examples include substituting the
<X> header for the <X.h> header for C++ includes, or <iostream> instead
of the deprecated header <iostream.h>. To disable this warning use
-Wno-deprecated.
New:
#ifdef I_USE_WINDOWS
#include <ostream> // OLD: #include <ostream.h>
#include <istream> // OLD: #include <istream.h>
#include <iostream> // error: `cout' undeclared (first use this
function)
using namespace std; // error: `cout' undeclared (first use this function)
#endif
Strange Errors
==============
error: ISO C++ forbids declaration of `Q3PtrList' with no typ
error: expected `;' before '<' token
Q3PtrList<my> myList;
This strange compiler (g++) message means: "my> myList" is not known.
Do a #include <Q3PtrList>.
Old:
QApsSettings() { myList.setAutoDelete(true); }
Qt 2.3:
mylist.setAutoDelete( TRUE );
// delete items when they are removed
// See: http://doc.trolltech.com/2.3/qlist.html
New:
QApsSettings() { } // setAutoDelete Not needed.
QList
=====
Change every QList to Q3PtrList. This is not done by the
converter(qt3to4.exe) from Trolltech.
QList -> Q3PtrList
Old:
QList<my> myList;
New:
Q3PtrList<my> myList;
NOTE:
declare:
Q3PtrList<my> myList; // [Qt2] QList<my> myList;
then comment:
// myList.setAutoDelete( true ); // [Qt4] not used anymore
QRegExp
=======
Maybe you have to include
#include <QRegExp>
QString string;
QRegExp regSection("\\[[^]]*\\]"); // match a "[section]"
Old Qt2:
i=regSection.match(string, i, &el);
(See http://doc.trolltech.com/3.0/qregexp.html#match)
New Qt4:
i=regSection.search(string, i);
Old Qt2:
my1 = string.mid(i+1, el-2);
i+=el;
New Qt4:
my1 = string.mid(i+1, regSection.matchedLength()-2 );
Note you can use matchedLength() instead of the &el things.
Maybe print out some values to the console for checking/debugging with:
#include <QDebug>
cout << "createGUI(): start..." << endl;
...
qDebug("GUI. created.");
QString
=======
error: invalid conversion from `QChar*' to `char' (g++)
-------------------------------------------------
Old Qt2:
QString str1 = "";
QString str2 = "";
str1 = str2.data();
New Qt4:
QString str1 = "";
QString str2 = "";
str1 = str2;
QLabel
======
Add namespace "QTt::"
->setAlignment(Qt::AlignHCenter|Qt::AlignTop); // Qt2.3: AlignHCenter -
QSplit
======
Seems to work differently.
Just try other things, look in examples, etc.
7. After a while of debugging and changeing source code, you should
recompile everything.
Do:
make clean
make release // or make debug
But note: Maybe you have to change things in the Makefile.release
directly, so, do a backup before you need to recompile everything.
8. Still some minor problems exist. Some new Q-Things beheave different.
Porting from 2 to 4 is possible. Check also archive of qt-interest.
Hope this helps.
--
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