On Unix systems (including Mac OS X), QSettings uses text files to
store settings. On Windows systems, QSettings uses the system
registry.
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.
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:
- $QT_INSTALL_PREFIX/etc/settings
- /opt/MyCompany/share/etc
- /opt/MyCompany/share/MyApplication/etc
- $HOME/.qt
When reading settings the files are searched in the order shown
above, with later settings overriding earlier settings. Files for
which the user doesn't have read permission are ignored. When
saving settings QSettings works in the order shown above, writing
to the first settings file for which the user has write
permission. ($QT_INSTALL_PREFIX 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 multiplatform applications you should ensure that the Windows
size limitations are not exceeded.
See also Input/Output and Networking and Miscellaneous Classes.
Member Type Documentation
QSettings::System
- QSettings::Mac - Macintosh execution environments (internal)
- 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.
QSettings::~QSettings ()
Destroys the settings object. All modifications made to the
settings will automatically be saved.
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 keys.
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 = entryList( "/MyCompany/MyApplication" );
keys contains 'background color' and 'foreground color'. It does
not contain 'geometry' because that key contains keys not entries.
To access the geometry values either use subkeyList() to read the
keys and then read each entry, or simply read each entry directly
by specifying its full key, e.g.
"/MyCompany/MyApplication/geometry/y".
See also subkeyList().
void QSettings::insertSearchPath ( System s, const QString & path )
Inserts path into the settings search path. The semantics of path depends on the system s.
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:
- $QTDIR/etc - where $QTDIR is the directory where Qt was installed.
- $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:
- $QTDIR/etc
- /opt/MyCompany/share/etc
- /opt/MyCompany/share/MyApplication/etc
- $HOME/.qt
When reading settings the files are searched in the order shown
above, with later settings overriding earlier settings. Files for
which the user doesn't have read permission are ignored. When
saving settings QSettings works in the order as shown above,
writing to the first settings file for which the user has write
permission. ($QTDIR is the directory where Qt was installed.)
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 = 0, bool * ok = 0 )
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
not 0: *ok is set to TRUE if the key was read, otherwise *ok
is set to FALSE.
See also readEntry(), readNumEntry(), readDoubleEntry(), writeEntry() and removeEntry().
double QSettings::readDoubleEntry ( const QString & key, double def = 0, bool * ok = 0 )
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
not 0: *ok is set to TRUE if the key was read, otherwise *ok
is set to FALSE.
See also readEntry(), readNumEntry(), readBoolEntry(), writeEntry() and removeEntry().
QString QSettings::readEntry ( const QString & key, const QString & def = QString::null, bool * ok = 0 )
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
not 0: *ok is set to TRUE if the key was read, otherwise *ok
is set to FALSE.
See also readListEntry(), readNumEntry(), readDoubleEntry(), readBoolEntry(), writeEntry() and removeEntry().
Example: chart/chartform.cpp.
QStringList QSettings::readListEntry ( const QString & key, bool * ok = 0 )
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 )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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.
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 )
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 not 0: *ok is set to TRUE if the key was read, otherwise *ok
is set to FALSE.
See also readEntry(), readDoubleEntry(), readBoolEntry(), writeEntry() and removeEntry().
Example: chart/chartform.cpp.
bool QSettings::removeEntry ( const QString & key )
Removes the entry specified by key.
Returns FALSE if the entry existed and could not be removed;
otherwise returns TRUE.
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().
QStringList QSettings::subkeyList ( const QString & key ) const
Returns a list of the keys which contain keys 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 = subkeyList( "/MyCompany/MyApplication" );
keys contains 'geometry' and 'recent files'. It does not
contain 'background color' or 'foreground color' because they are
keys which contain entries not keys. To get a list of keys that
have values rather than subkeys use entryList().
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 returns TRUE.
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 returns TRUE.
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 returns TRUE.
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 returns TRUE.
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.
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, 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.
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 file is part of the Qt toolkit.
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