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The QSettings class provides persistent platform-independent application settings. More...
#include <qsettings.h>
On Unix systems, QSettings uses text files to store settings. On Windows systems, QSettings uses the system registry. On Mac OS X, QSettings 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 QSettings to save the settings for each individual application and QSessionManager 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:
QSettings settings;
settings.setPath( "MyCompany.com", "MyApplication" );
QString 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':
QSettings 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:
QSettings 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().
QStringList keys = settings.entryList( "/MyApplication" );
// keys contains 'background color' and 'foreground color'.
QStringList keys = settings.entryList( "/MyApplication/recent files" );
// keys contains '1', '2' and '3'.
QStringList subkeys = settings.subkeyList( "/MyApplication" );
// subkeys contains 'geometry' and 'recent files'
QStringList 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:
These limitations are not enforced on Unix or Mac OS X.
Warning: Creating multiple, simultaneous instances of QSettings writing to a text file may lead to data loss! This is a known issue which will be fixed in a future release of Qt.
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). QSettings 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
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:
If you want to put the settings in a particular place in the filesystem you could do this:
settings.insertSearchPath( QSettings::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: QSettings doesn't write the settings until it is destroyed so you should construct the QSettings object on the stack.
See also Input/Output and Networking and Miscellaneous Classes.
Be aware that you must call setPath() or insertSearchPath() before you can use the QSettings object.
Be aware that you must call setPath() or insertSearchPath() before you can use the QSettings object.
QSettings settings;
settings.beginGroup( "/MainWindow" );
// read values
settings.endGroup();
QSettings settings;
settings.beginGroup( "/MainWindow/Geometry" );
// read values
settings.endGroup();
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
QStringList 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().
See also beginGroup().
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.
QSettings settings; settings.insertSearchPath( QSettings::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.
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:
All insertions into the search path will go before $HOME/.qt/. For example:
QSettings settings; settings.insertSearchPath( QSettings::Unix, "/opt/MyCompany/share/etc" ); settings.insertSearchPath( QSettings::Unix, "/opt/MyCompany/share/MyApplication/etc" ); // ...Will result in a search path of:
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.
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().
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().
Reads the entry specified by key, and returns a QString, 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().
Note that if you want to iterate over the list, you should iterate over a copy, e.g.
QStringList list = mySettings.readListEntry( "recentfiles" );
QStringList::Iterator it = list.begin();
while( it != list.end() ) {
myProcessing( *it );
++it;
}
See also readEntry(), readDoubleEntry(), readBoolEntry(), writeEntry(), removeEntry(), and QStringList::split().
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 QStringList by calling QStringList::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, QStringList::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.
QStringList list = mySettings.readListEntry( "size", " " );
QStringList::Iterator it = list.begin();
while( it != list.end() ) {
myProcessing( *it );
++it;
}
See also readEntry(), readDoubleEntry(), readBoolEntry(), writeEntry(), removeEntry(), and QStringList::split().
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().
Returns FALSE if the entry was unable to be removed.
See also readEntry() and writeEntry().
See also insertSearchPath().
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 QSettings::User for user-specific settings, or QSettings::Global for system-wide settings (generally these will be read-only to many users).
Not all information is relevant on all systems.
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
QStringList 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 QSettings 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 coloris 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 QSettings. This is a known issue which will be fixed in Qt-4.
See also entryList().
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().
Example: chart/chartform.cpp.
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().
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().
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().
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().
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 QStringList::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 QStringList::split() to recreate the list. As the documentation states, QStringList::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 QStringList::join().
This file is part of the Qt toolkit. Copyright © 1995-2005 Trolltech. All Rights Reserved.
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