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.
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:
- SYSCONF - the default value is INSTALL/etc/settings
- /opt/MyCompany/share/etc
- /opt/MyCompany/share/MyApplication/etc
- $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 QSettings works in the order shown above, writing
to the first settings file for which the user has write permission.
(INSTALL is the directory where Qt 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( 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.
Member Type Documentation
QSettings::Format
- QSettings::Native - Store the settings in a platform dependent location
- QSettings::Ini - Store the settings in a text file
QSettings::Scope
- QSettings::Global - Save settings as global as possible
- QSettings::User - Save settings in user space
QSettings::System
- QSettings::Mac - Macintosh execution environments
- QSettings::Unix - Mac OS X, Unix, Linux and Unix-like execution environments
- QSettings::Windows - Windows execution environments
Member Function Documentation
QSettings::QSettings ()
Creates a settings object.
Be aware that you must call setPath() or insertSearchPath() before
you can use the QSettings object.
QSettings::QSettings ( 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 QSettings object.
QSettings::~QSettings ()
Destroys the settings object. All modifications made to the settings
will automatically be saved.
void QSettings::beginGroup ( const QString & group )
Appends group to the current key prefix.
QSettings settings;
settings.beginGroup( "/MainWindow" );
// read values
settings.endGroup();
void QSettings::endGroup ()
Undo previous calls to beginGroup(). Note that a single beginGroup("a/b/c") is undone
by a single call to endGroup().
QSettings settings;
settings.beginGroup( "/MainWindow/Geometry" );
// read values
settings.endGroup();
QStringList QSettings::entryList ( const QString & 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
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().
QString QSettings::group () const
Returns the current key prefix, or a null string if there is no key prefix set.
See also beginGroup().
void QSettings::insertSearchPath ( System s, const QString & 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.
- HKEY_CURRENT_USER/Software/MyCompany/MyApplication
- HKEY_LOCAL_MACHINE/Software/MyCompany/MyApplication
- HKEY_CURRENT_USER/Software/MyApplication
- HKEY_LOCAL_MACHINE/Software/MyApplication
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.
- HKEY_LOCAL_MACHINE/Software/MyCompany/MyApplication
- HKEY_CURRENT_USER/Software/MyCompany/MyApplication
- HKEY_LOCAL_MACHINE/Software/MyApplication
- 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:
- SYSCONF - where SYSCONF is a directory specified when
configuring Qt; by default it is INSTALL/etc/settings.
- $HOME/.qt/ - where $HOME is the user's home directory.
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:
- SYSCONF
- /opt/MyCompany/share/etc
- /opt/MyCompany/share/MyApplication/etc
- $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 QSettings 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 QSettings::readBoolEntry ( const QString & 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 QSettings::readDoubleEntry ( const QString & 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().
QString QSettings::readEntry ( const QString & key, const QString & def = QString::null, bool * ok = 0 ) const
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().
QStringList QSettings::readListEntry ( const QString & 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.
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().
QStringList QSettings::readListEntry ( const QString & key, const QChar & 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 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().
int QSettings::readNumEntry ( const QString & 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 QSettings::removeEntry ( const QString & key )
Removes the entry specified by key.
Returns FALSE if the entry was unable to be removed.
See also readEntry() and writeEntry().
void QSettings::removeSearchPath ( System s, const QString & 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 QSettings::resetGroup ()
Set the current key prefix to the empty string.
void QSettings::setPath ( const QString & domain, const QString & 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
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.
QStringList QSettings::subkeyList ( const QString & 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
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 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 QSettings. This is a known issue which
will be fixed in Qt-4.
See also entryList().
bool QSettings::writeEntry ( const QString & 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.
See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), and removeEntry().
Example: chart/chartform.cpp.
bool QSettings::writeEntry ( const QString & 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 QSettings::writeEntry ( const QString & 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 QSettings::writeEntry ( const QString & key, const QString & 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 QSettings::writeEntry ( const QString & key, const QStringList & 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 QSettings::writeEntry ( const QString & key, const QStringList & value, const QChar & 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 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.
