TQSettings Class

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# TQSettings Class Reference

The TQSettings class provides persistent platform-independent application settings. More...

`#include <tqsettings.h>`

List of all member functions.

## Public Members

- enum Format { Native = 0, Ini }
- enum System { Unix = 0, Windows, Mac }
- enum Scope { User, Global }
- TQSettings ()
- TQSettings ( Format format )
- ~TQSettings ()
- bool writeEntry ( const TQString & key, bool value )
- bool writeEntry ( const TQString & key, double value )
- bool writeEntry ( const TQString & key, int value )
- bool writeEntry ( const TQString & key, const TQString & value )
- bool writeEntry ( const TQString & key, const TQStringList & value )
- bool writeEntry ( const TQString & key, const TQStringList & value, const TQChar & separator ) (obsolete)
- TQStringList entryList ( const TQString & key ) const
- TQStringList subkeyList ( const TQString & key ) const
- TQStringList readListEntry ( const TQString & key, bool * ok = 0 ) const
- TQStringList readListEntry ( const TQString & key, const TQChar & separator, bool * ok = 0 ) const (obsolete)
- TQString readEntry ( const TQString & key, const TQString & def = TQString::null, bool * ok = 0 ) const
- int readNumEntry ( const TQString & key, int def = 0, bool * ok = 0 ) const
- double readDoubleEntry ( const TQString & key, double def = 0, bool * ok = 0 ) const
- bool readBoolEntry ( const TQString & key, bool def = false, bool * ok = 0 ) const
- bool removeEntry ( const TQString & key )
- void insertSearchPath ( System s, const TQString & path )
- void removeSearchPath ( System s, const TQString & path )
- void setPath ( const TQString & domain, const TQString & product, Scope scope = Global )
- void beginGroup ( const TQString & group )
- void endGroup ()
- void resetGroup ()
- TQString group () const

## Detailed Description

The TQSettings class provides persistent platform-independent application settings.

On Unix systems, TQSettings uses text files to store settings. On Windows systems, TQSettings uses the system registry. On Mac OS X, TQSettings uses the Carbon preferences API.

Each setting comprises an identifying key and the data associated with the key. A key is a unicode string which consists of two or more subkeys. A subkey is a slash, '/', followed by one or more unicode characters (excluding slashes, newlines, carriage returns and equals, '=', signs). The associated data, called the entry or value, may be a boolean, an integer, a double, a string or a list of strings. Entry strings may contain any unicode characters.

If you want to save and restore the entire desktop's settings, i.e. which applications are running, use TQSettings to save the settings for each individual application and TQSessionManager to save the desktop's session.

Example settings:

        /MyCompany/MyApplication/background color
        /MyCompany/MyApplication/foreground color
        /MyCompany/MyApplication/geometry/x
        /MyCompany/MyApplication/geometry/y
        /MyCompany/MyApplication/geometry/width
        /MyCompany/MyApplication/geometry/height
        /MyCompany/MyApplication/recent files/1
        /MyCompany/MyApplication/recent files/2
        /MyCompany/MyApplication/recent files/3

Each line above is a complete key, made up of subkeys.

A typical usage pattern for reading settings at application startup:

        TQSettings settings;
        settings.setPath( "MyCompany.com", "MyApplication" );

        TQString bgColor = settings.readEntry( "/colors/background", "white" );
        int width = settings.readNumEntry( "/geometry/width", 640 );
        // ...

A typical usage pattern for saving settings at application exit or 'save preferences':

        TQSettings settings;
        settings.setPath( "MyCompany.com", "MyApplication" );

        settings.writeEntry( "/colors/background", bgColor );
        settings.writeEntry( "/geometry/width", width );
        // ...

A key prefix can be prepended to all keys using beginGroup(). The application of the prefix is stopped using endGroup(). For example:

        TQSettings settings;

        settings.beginGroup( "/MainWindow" );
            settings.beginGroup( "/Geometry" );
                int x = settings.readEntry( "/x" );
                // ...
            settings.endGroup();
            settings.beginGroup( "/Toolbars" );
                // ...
            settings.endGroup();
        settings.endGroup();

You can get a list of entry-holding keys by calling entryList(), and a list of key-holding keys using subkeyList().

        TQStringList keys = settings.entryList( "/MyApplication" );
        // keys contains 'background color' and 'foreground color'.

        TQStringList keys = settings.entryList( "/MyApplication/recent files" );
        // keys contains '1', '2' and '3'.

        TQStringList subkeys = settings.subkeyList( "/MyApplication" );
        // subkeys contains 'geometry' and 'recent files'

        TQStringList subkeys = settings.subkeyList( "/MyApplication/recent files" );
        // subkeys is empty.

Since settings for Windows are stored in the registry there are some size limitations as follows:

- A subkey may not exceed 255 characters.
- An entry's value may not exceed 16,300 characters.
- All the values of a key (for example, all the 'recent files' subkeys values), may not exceed 65,535 characters.

These limitations are not enforced on Unix or Mac OS X.

Warning: Creating multiple, simultaneous instances of TQSettings writing to a text file may lead to data loss! This is a known issue which will be fixed in a future release of TQt.

### Notes for Mac OS X Applications

The location where settings are stored is not formally defined by the CFPreferences API.

At the time of writing settings are stored (either on a global or user basis, preferring locally) into a plist file in `$ROOT/System/Library/Preferences` (in XML format). TQSettings will create an appropriate plist file (`com.<first group name>.plist`) out of the full path to a key.

For further information on CFPreferences see Apple's Specifications

### Notes for Unix Applications

There is no universally accepted place for storing application settings under Unix. In the examples the settings file will be searched for in the following directories:

1. `SYSCONF` - the default value is `INSTALL/etc/settings`
2. `/opt/MyCompany/share/etc`
3. `/opt/MyCompany/share/MyApplication/etc`
4. `$HOME/.qt`

When reading settings the files are searched in the order shown above, with later settings overriding earlier settings. Files for which the user doesn't have read permission are ignored. When saving settings TQSettings works in the order shown above, writing to the first settings file for which the user has write permission. (`INSTALL` is the directory where TQt was installed. This can be modified by using the configure script's -prefix argument )

If you want to put the settings in a particular place in the filesystem you could do this:

        settings.insertSearchPath( TQSettings::Unix, "/opt/MyCompany/share" );

But in practice you may prefer not to use a search path for Unix. For example the following code:

        settings.writeEntry( "/MyApplication/geometry/width", width );

will end up writing the "geometry/width" setting to the file `$HOME/.qt/myapplicationrc` (assuming that the application is being run by an ordinary user, i.e. not by root).

For cross-platform applications you should ensure that the Windows size limitations are not exceeded.

Warning: TQSettings doesn't write the settings until it is destroyed so you should construct the TQSettings object on the stack.

See also Input/Output and Networking and Miscellaneous Classes.

## Member Type Documentation

### TQSettings::Format

- `TQSettings::Native` - Store the settings in a platform dependent location
- `TQSettings::Ini` - Store the settings in a text file

### TQSettings::Scope

- `TQSettings::Global` - Save settings as global as possible
- `TQSettings::User` - Save settings in user space

### TQSettings::System

- `TQSettings::Mac` - Macintosh execution environments
- `TQSettings::Unix` - Mac OS X, Unix, Linux and Unix-like execution environments
- `TQSettings::Windows` - Windows execution environments

## Member Function Documentation

### TQSettings::TQSettings ()

Creates a settings object.

Be aware that you must call setPath() or insertSearchPath() before you can use the TQSettings object.

### TQSettings::TQSettings ( Format format )

Creates a settings object. If format is 'Ini' the settings will be stored in a text file, using the Unix strategy (see above). If format is 'Native', the settings will be stored in a platform specific way (ie. the Windows registry).

Be aware that you must call setPath() or insertSearchPath() before you can use the TQSettings object.

### TQSettings::~TQSettings ()

Destroys the settings object. All modifications made to the settings will automatically be saved.

### void TQSettings::beginGroup ( const TQString & group )

Appends group to the current key prefix.

        TQSettings settings;
        settings.beginGroup( "/MainWindow" );
        // read values
        settings.endGroup();

### void TQSettings::endGroup ()

Undo previous calls to beginGroup(). Note that a single beginGroup("a/b/c") is undone by a single call to endGroup().

        TQSettings settings;
        settings.beginGroup( "/MainWindow/Geometry" );
        // read values
        settings.endGroup();

### TQStringList TQSettings::entryList ( const TQString & key ) const

Returns a list of the keys which contain entries under key. Does not return any keys that contain subkeys.

Example settings:

        /MyCompany/MyApplication/background color
        /MyCompany/MyApplication/foreground color
        /MyCompany/MyApplication/geometry/x
        /MyCompany/MyApplication/geometry/y
        /MyCompany/MyApplication/geometry/width
        /MyCompany/MyApplication/geometry/height

        TQStringList keys = settings.entryList( "/MyCompany/MyApplication" );

In the above example, `keys` will contain 'background color' and 'foreground color'. It will not contain 'geometry' because this key contains subkeys not entries.

To access the geometry values, you could either use subkeyList() to read the keys then read each entry, or simply read each entry directly by specifying its full key, e.g. "/MyCompany/MyApplication/geometry/y".

See also subkeyList().

### TQString TQSettings::group () const

Returns the current key prefix, or a null string if there is no key prefix set.

See also beginGroup().

### void TQSettings::insertSearchPath ( System s, const TQString & path )

Inserts path into the settings search path. The semantics of path depends on the system s. It is usually easier and better to use setPath() instead of this function.

When s is Windows and the execution environment is not Windows the function does nothing. Similarly when s is Unix and the execution environment is not Unix the function does nothing.

When s is Windows, and the execution environment is Windows, the search path list will be used as the first subfolder of the "Software" folder in the registry.

When reading settings the folders are searched forwards from the first folder (listed below) to the last, returning the first settings found, and ignoring any folders for which the user doesn't have read permission.

1. HKEY_CURRENT_USER/Software/MyCompany/MyApplication
2. HKEY_LOCAL_MACHINE/Software/MyCompany/MyApplication
3. HKEY_CURRENT_USER/Software/MyApplication
4. HKEY_LOCAL_MACHINE/Software/MyApplication

      TQSettings settings;
      settings.insertSearchPath( TQSettings::Windows, "/MyCompany" );
      settings.writeEntry( "/MyApplication/Tip of the day", true );

The code above will write the subkey "Tip of the day" into the first of the registry folders listed below that is found and for which the user has write permission.

1. HKEY_LOCAL_MACHINE/Software/MyCompany/MyApplication
2. HKEY_CURRENT_USER/Software/MyCompany/MyApplication
3. HKEY_LOCAL_MACHINE/Software/MyApplication
4. HKEY_CURRENT_USER/Software/MyApplication

If a setting is found in the HKEY_CURRENT_USER space, this setting is overwritten independently of write permissions in the HKEY_LOCAL_MACHINE space.

When s is Unix, and the execution environment is Unix, the search path list will be used when trying to determine a suitable filename for reading and writing settings files. By default, there are two entries in the search path:

1. `SYSCONF` - where `SYSCONF` is a directory specified when configuring TQt; by default it is INSTALL/etc/settings.
2. `$HOME/.qt/` - where `$HOME` is the user's home directory.

All insertions into the search path will go before $HOME/.qt/. For example:

      TQSettings settings;
      settings.insertSearchPath( TQSettings::Unix, "/opt/MyCompany/share/etc" );
      settings.insertSearchPath( TQSettings::Unix, "/opt/MyCompany/share/MyApplication/etc" );
      // ...

Will result in a search path of:

1. SYSCONF
2. /opt/MyCompany/share/etc
3. /opt/MyCompany/share/MyApplication/etc
4. $HOME/.qt

When reading settings the files are searched in the order shown above, with later settings overriding earlier settings. Files for which the user doesn't have read permission are ignored. When saving settings TQSettings works in the order shown above, writing to the first settings file for which the user has write permission.

Note that paths in the file system are not created by this function, so they must already exist to be useful.

Settings under Unix are stored in files whose names are based on the first subkey of the key (not including the search path). The algorithm for creating names is essentially: lowercase the first subkey, replace spaces with underscores and add 'rc', e.g. `/MyCompany/MyApplication/background color` will be stored in `myapplicationrc` (assuming that `/MyCompany` is part of the search path).

See also removeSearchPath().

Example: chart/chartform.cpp.

### bool TQSettings::readBoolEntry ( const TQString & key, bool def = false, bool * ok = 0 ) const

Reads the entry specified by key, and returns a bool, or the default value, def, if the entry couldn't be read. If ok is non-null, *ok is set to true if the key was read, false otherwise.

See also readEntry(), readNumEntry(), readDoubleEntry(), writeEntry(), and removeEntry().

### double TQSettings::readDoubleEntry ( const TQString & key, double def = 0, bool * ok = 0 ) const

Reads the entry specified by key, and returns a double, or the default value, def, if the entry couldn't be read. If ok is non-null, *ok is set to true if the key was read, false otherwise.

See also readEntry(), readNumEntry(), readBoolEntry(), writeEntry(), and removeEntry().

### TQString TQSettings::readEntry ( const TQString & key, const TQString & def = TQString::null, bool * ok = 0 ) const

Reads the entry specified by key, and returns a TQString, or the default value, def, if the entry couldn't be read. If ok is non-null, *ok is set to true if the key was read, false otherwise.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), writeEntry(), and removeEntry().

### TQStringList TQSettings::readListEntry ( const TQString & key, bool * ok = 0 ) const

Reads the entry specified by key as a string. If ok is not 0, *ok is set to true if the key was read, otherwise *ok is set to false.

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

        TQStringList list = mySettings.readListEntry( "recentfiles" );
        TQStringList::Iterator it = list.begin();
        while( it != list.end() ) {
            myProcessing( *it );
            ++it;
        }

See also readEntry(), readDoubleEntry(), readBoolEntry(), writeEntry(), removeEntry(), and TQStringList::split().

### TQStringList TQSettings::readListEntry ( const TQString & key, const TQChar & separator, bool * ok = 0 ) const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

Reads the entry specified by key as a string. The separator is used to create a TQStringList by calling TQStringList::split(separator, entry). If ok is not 0: *ok is set to true if the key was read, otherwise *ok is set to false.

Warning: As the documentation states, TQStringList::split() will omit empty strings from the list. Because of this, it is impossible to retrieve identical list data with this function. We recommend using the readListEntry() and writeEntry() overloads that do not take a separator argument.

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

        TQStringList list = mySettings.readListEntry( "size", " " );
        TQStringList::Iterator it = list.begin();
        while( it != list.end() ) {
            myProcessing( *it );
            ++it;
        }

See also readEntry(), readDoubleEntry(), readBoolEntry(), writeEntry(), removeEntry(), and TQStringList::split().

### int TQSettings::readNumEntry ( const TQString & key, int def = 0, bool * ok = 0 ) const

Reads the entry specified by key, and returns an integer, or the default value, def, if the entry couldn't be read. If ok is non-null, *ok is set to true if the key was read, false otherwise.

See also readEntry(), readDoubleEntry(), readBoolEntry(), writeEntry(), and removeEntry().

### bool TQSettings::removeEntry ( const TQString & key )

Removes the entry specified by key.

Returns true if the entry was successfully removed; otherwise returns false. Note that removing the last entry in any given folder, will also remove the folder.

See also readEntry() and writeEntry().

### void TQSettings::removeSearchPath ( System s, const TQString & path )

Removes all occurrences of path (using exact matching) from the settings search path for system s. Note that the default search paths cannot be removed.

See also insertSearchPath().

### void TQSettings::resetGroup ()

Set the current key prefix to the empty string.

### void TQSettings::setPath ( const TQString & domain, const TQString & product, Scope scope = Global )

Insert platform-dependent paths from platform-independent information.

The domain should be an Internet domain name controlled by the producer of the software, eg. Trolltech products use "trolltech.com".

The product should be the official name of the product.

The scope should be TQSettings::User for user-specific settings, or TQSettings::Global for system-wide settings (generally these will be read-only to many users).

Not all information is relevant on all systems.

### TQStringList TQSettings::subkeyList ( const TQString & key ) const

Returns a list of the keys which contain subkeys under key. Does not return any keys that contain entries.

Example settings:

        /MyCompany/MyApplication/background color
        /MyCompany/MyApplication/foreground color
        /MyCompany/MyApplication/geometry/x
        /MyCompany/MyApplication/geometry/y
        /MyCompany/MyApplication/geometry/width
        /MyCompany/MyApplication/geometry/height
        /MyCompany/MyApplication/recent files/1
        /MyCompany/MyApplication/recent files/2
        /MyCompany/MyApplication/recent files/3

        TQStringList keys = settings.subkeyList( "/MyCompany/MyApplication" );

In the above example, `keys` will contain 'geometry' and 'recent files'. It will not contain 'background color' or 'foreground color' because those keys contain entries not subkeys. To get a list of keys that contain entries rather than subkeys use entryList() instead.

Warning: In the above example, if TQSettings is writing to an Ini file, then a call to

     subkeyList("/MyCompany")

will return an empty list. This happens because a key like

     /MyCompany/MyApplication/background color

is written to the file "mycompanyrc", under the section [MyApplication]. This call is therefore a request to list the sections in an ini file, which is not supported in this version of TQSettings. This is a known issue which will be fixed in TQt-4.

See also entryList().

### bool TQSettings::writeEntry ( const TQString & key, bool value )

Writes the boolean entry value into key key. The key is created if it doesn't exist. Any previous value is overwritten by value.

If an error occurs the settings are left unchanged and false is returned; otherwise true is returned.

Warning: On certain platforms, keys are required to contain at least two components (e.g., "/foo/bar"). This limitation does not apply to TQt 4.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), and removeEntry().

Example: chart/chartform.cpp.

### bool TQSettings::writeEntry ( const TQString & key, double value )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes the double entry value into key key. The key is created if it doesn't exist. Any previous value is overwritten by value.

If an error occurs the settings are left unchanged and false is returned; otherwise true is returned.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), and removeEntry().

### bool TQSettings::writeEntry ( const TQString & key, int value )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes the integer entry value into key key. The key is created if it doesn't exist. Any previous value is overwritten by value.

If an error occurs the settings are left unchanged and false is returned; otherwise true is returned.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), and removeEntry().

### bool TQSettings::writeEntry ( const TQString & key, const TQString & value )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes the string entry value into key key. The key is created if it doesn't exist. Any previous value is overwritten by value. If value is an empty string or a null string the key's value will be an empty string.

If an error occurs the settings are left unchanged and false is returned; otherwise true is returned.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), and removeEntry().

### bool TQSettings::writeEntry ( const TQString & key, const TQStringList & value )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes the string list entry value into key key. The key is created if it doesn't exist. Any previous value is overwritten by value.

If an error occurs the settings are left unchanged and false is returned; otherwise returns true.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), and removeEntry().

### bool TQSettings::writeEntry ( const TQString & key, const TQStringList & value, const TQChar & separator )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

Writes the string list entry value into key key. The key is created if it doesn't exist. Any previous value is overwritten by value. The list is stored as a sequence of strings separated by separator (using TQStringList::join()), so none of the strings in the list should contain the separator. If the list is empty or null the key's value will be an empty string.

Warning: The list should not contain empty or null strings, as readListEntry() will use TQStringList::split() to recreate the list. As the documentation states, TQStringList::split() will omit empty strings from the list. Because of this, it is impossible to retrieve identical list data that is stored with this function. We recommend using the writeEntry() and readListEntry() overloads that do not take a separator argument.

If an error occurs the settings are left unchanged and false is returned; otherwise returns true.

See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), removeEntry(), and TQStringList::join().

This file is part of the TQt toolkit. Copyright © 1995-2007 Trolltech. All Rights Reserved.