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# qt3to4 - The Qt 3 to 4 Porting Tool

The `qt3to4` tool provides help when moving a project from Qt 3 to Qt 4. It is designed to automate the most tedious part of the porting effort.

See the Porting Guide for more information about porting from Qt 3 to Qt 4.

## Usage

`qt3to4` can be run either on individual C++ source or header files, or on an entire project specified by a qmake `.pro` file:

        qt3to4 myfile.cpp
        qt3to4 myapp.pro

In project mode, `qt3to4` reads the `.pro` file and converts all files specified in it. The tool modifies the files in place. You might want to make a copy of your project before you run the tool.

## Porting Rules

The Qt porting tool loads its porting rules from an XML file called `q3porting.xml` located in Qt's `tools/porting/src` directory. By editing this file, you can add your own rules or remove some rules.

The standard `q3porting.xml` file specifies the following conversions:

- Rename classes that are now part of the Qt 3 support library (e.g., replace `QFileDialog` with `Q3FileDialog`).
- Prefix or rename enum values that have been moved or renamed (e.g., replace `QButton::On` with `QCheckBox::On`) or members of the Qt namespace (e.g., replace `QWidget::red` with `Qt::red`).
- Add `#include` directives that might be needed in Qt 4.

### Location of the qt3porting.xml File

You can now specify the location of the `qt3porting.xml` file with the `-f` command line option. This is useful if you want to use a modified file with your own rules.

If you you don't want to maintain a modified `qt3porting.xml` it is possible to create a "patch" file that includes the original file and adds or disables rules. The syntax for this file looks like this:

        <Rules>
          <Include>/path/to/q3porting.xml</Include>

          <item Type="RenamedHeader" Disable="True" >
            <Qt4>q3sqlselectcursor.h</Qt4>
            <Qt3>qsqlselectcursor.h</Qt3>
          </item>

          <item Type="RenamedHeader" >
            <Qt4>newclass.h</Qt4>
            <Qt3>oldclass.h</Qt3>
          </item>
        </Rules>

## Logging

The porting tool logs all changes to a file called `portinglog.txt` in the current directory. This file lists all changes made to the source files.

## Advanced Usage

When porting, qt3to4 parses the source files and ports the contents according to the C++ language rules. This C++ parsing step can be disabled with the -disableCppParsing option.

If C++ parsing is enabled, qt3to4 must be able to locate the headers included from the source files. Necessary headers include the public Qt headers and any headers that declares names that may conflict with names in the public Qt headers. The standard C++ headers and system headers are usually not needed.

You can tell qt3to4 where to look for headers by using the `-I` command line option. Qt 3.3 header information is built in, so it is normaly not neccesary to specify the location of the Qt headers. If you are porting from a different version of Qt 3, you may want to disable the built-in headers with `-disableBuiltInQt3Headers`, and then add the path to the actual headers with the `-I` option.

When porting a project, qt3to4 will read the INCLUDEPATH and DEPENDPATH variables from the .pro file and add the paths specified here to the list of include search directories.

To see which headers that are not found, use the `-missingFileWarnings` option.