QSettings Class

Member Function Documentation

QSettings::QSettings(QSettings::Scope scope, QObject *parent = nullptr)

Constructs a QSettings object in the same way as QSettings(QObject *parent) but with the given scope.

This function was introduced in Qt 5.13.

See also QSettings(QObject *parent).

QSettings::QSettings(QObject *parent = nullptr)

Constructs a QSettings object for accessing settings of the application and organization set previously with a call to QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), and QCoreApplication::setApplicationName().

The scope is QSettings::UserScope and the format is defaultFormat() (QSettings::NativeFormat by default). Use setDefaultFormat() before calling this constructor to change the default format used by this constructor.

The code

QSettings settings("Moose Soft", "Facturo-Pro");

is equivalent to

QCoreApplication::setOrganizationName("Moose Soft");
QCoreApplication::setApplicationName("Facturo-Pro");
QSettings settings;

If QCoreApplication::setOrganizationName() and QCoreApplication::setApplicationName() has not been previously called, the QSettings object will not be able to read or write any settings, and status() will return AccessError.

You should supply both the domain (used by default on macOS and iOS) and the name (used by default elsewhere), although the code will cope if you supply only one, which will then be used (on all platforms), at odds with the usual naming of the file on platforms for which it isn't the default.

See also QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), QCoreApplication::setApplicationName(), and setDefaultFormat().

QSettings::QSettings(const QString &fileName, QSettings::Format format, QObject *parent = nullptr)

Constructs a QSettings object for accessing the settings stored in the file called fileName, with parent parent. If the file doesn't already exist, it is created.

If format is QSettings::NativeFormat, the meaning of fileName depends on the platform. On Unix, fileName is the name of an INI file. On macOS and iOS, fileName is the name of a .plist file. On Windows, fileName is a path in the system registry.

If format is QSettings::IniFormat, fileName is the name of an INI file.

• QSettings provides no way of reading INI "path" entries, i.e., entries with unescaped slash characters. (This is because these entries are ambiguous and cannot be resolved automatically.)
• In INI files, QSettings uses the @ character as a metacharacter in some contexts, to encode Qt-specific data types (e.g., @Rect), and might therefore misinterpret it when it occurs in pure INI files.

See also fileName().

QSettings::QSettings(QSettings::Format format, QSettings::Scope scope, const QString &organization, const QString &application = QString(), QObject *parent = nullptr)

Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope, the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope, the QSettings object ignores user-specific settings and provides access to system-wide settings.

If format is QSettings::NativeFormat, the native API is used for storing settings. If format is QSettings::IniFormat, the INI format is used.

If no application name is given, the QSettings object will only access the organization-wide locations.

QSettings::QSettings(QSettings::Scope scope, const QString &organization, const QString &application = QString(), QObject *parent = nullptr)

Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope, the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope, the QSettings object ignores user-specific settings and provides access to system-wide settings.

The storage format is set to QSettings::NativeFormat (i.e. calling setDefaultFormat() before calling this constructor has no effect).

If no application name is given, the QSettings object will only access the organization-wide locations.

See also setDefaultFormat().

QSettings::QSettings(const QString &organization, const QString &application = QString(), QObject *parent = nullptr)

Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

Example:

QSettings settings("Moose Tech", "Facturo-Pro");

The scope is set to QSettings::UserScope, and the format is set to QSettings::NativeFormat (i.e. calling setDefaultFormat() before calling this constructor has no effect).

See also setDefaultFormat() and Fallback Mechanism.

[virtual] QSettings::~QSettings()

Destroys the QSettings object.

Any unsaved changes will eventually be written to permanent storage.

See also sync().

QStringList QSettings::allKeys() const

Returns a list of all keys, including subkeys, that can be read using the QSettings object.

Example:

QSettings settings;
settings.setValue("fridge/color", QColor(Qt::white));
settings.setValue("fridge/size", QSize(32, 96));
settings.setValue("sofa", true);
settings.setValue("tv", false);

QStringList keys = settings.allKeys();
// keys: ["fridge/color", "fridge/size", "sofa", "tv"]

If a group is set using beginGroup(), only the keys in the group are returned, without the group prefix:

settings.beginGroup("fridge");
keys = settings.allKeys();
// keys: ["color", "size"]

See also childGroups() and childKeys().

QString QSettings::applicationName() const

Returns the application name used for storing the settings.

This function was introduced in Qt 4.4.

See also QCoreApplication::applicationName(), format(), scope(), and organizationName().

void QSettings::beginGroup(const QString &prefix)

Appends prefix to the current group.

The current group is automatically prepended to all keys specified to QSettings. In addition, query functions such as childGroups(), childKeys(), and allKeys() are based on the group. By default, no group is set.

Groups are useful to avoid typing in the same setting paths over and over. For example:

settings.beginGroup("mainwindow");
settings.setValue("size", win->size());
settings.setValue("fullScreen", win->isFullScreen());
settings.endGroup();

settings.beginGroup("outputpanel");
settings.setValue("visible", panel->isVisible());
settings.endGroup();

This will set the value of three settings:

• mainwindow/size
• mainwindow/fullScreen
• outputpanel/visible

Call endGroup() to reset the current group to what it was before the corresponding beginGroup() call. Groups can be nested.

See also endGroup() and group().

int QSettings::beginReadArray(const QString &prefix)

Adds prefix to the current group and starts reading from an array. Returns the size of the array.

Example:

struct Login {
    QString userName;
    QString password;
};
QList<Login> logins;
...

QSettings settings;
int size = settings.beginReadArray("logins");
for (int i = 0; i < size; ++i) {
    settings.setArrayIndex(i);
    Login login;
    login.userName = settings.value("userName").toString();
    login.password = settings.value("password").toString();
    logins.append(login);
}
settings.endArray();

Use beginWriteArray() to write the array in the first place.

See also beginWriteArray(), endArray(), and setArrayIndex().

void QSettings::beginWriteArray(const QString &prefix, int size = -1)

Adds prefix to the current group and starts writing an array of size size. If size is -1 (the default), it is automatically determined based on the indexes of the entries written.

If you have many occurrences of a certain set of keys, you can use arrays to make your life easier. For example, let's suppose that you want to save a variable-length list of user names and passwords. You could then write:

struct Login {
    QString userName;
    QString password;
};
QList<Login> logins;
...

QSettings settings;
settings.beginWriteArray("logins");
for (int i = 0; i < logins.size(); ++i) {
    settings.setArrayIndex(i);
    settings.setValue("userName", list.at(i).userName);
    settings.setValue("password", list.at(i).password);
}
settings.endArray();

The generated keys will have the form

• logins/size
• logins/1/userName
• logins/1/password
• logins/2/userName
• logins/2/password
• logins/3/userName
• logins/3/password
• ...

To read back an array, use beginReadArray().

See also beginReadArray(), endArray(), and setArrayIndex().

QStringList QSettings::childGroups() const

Returns a list of all key top-level groups that contain keys that can be read using the QSettings object.

Example:

QSettings settings;
settings.setValue("fridge/color", QColor(Qt::white));
settings.setValue("fridge/size", QSize(32, 96));
settings.setValue("sofa", true);
settings.setValue("tv", false);

QStringList groups = settings.childGroups();
// groups: ["fridge"]

If a group is set using beginGroup(), the first-level keys in that group are returned, without the group prefix.

settings.beginGroup("fridge");
groups = settings.childGroups();
// groups: []

You can navigate through the entire setting hierarchy using childKeys() and childGroups() recursively.

See also childKeys() and allKeys().

QStringList QSettings::childKeys() const

Returns a list of all top-level keys that can be read using the QSettings object.

Example:

QSettings settings;
settings.setValue("fridge/color", QColor(Qt::white));
settings.setValue("fridge/size", QSize(32, 96));
settings.setValue("sofa", true);
settings.setValue("tv", false);

QStringList keys = settings.childKeys();
// keys: ["sofa", "tv"]

If a group is set using beginGroup(), the top-level keys in that group are returned, without the group prefix:

settings.beginGroup("fridge");
keys = settings.childKeys();
// keys: ["color", "size"]

You can navigate through the entire setting hierarchy using childKeys() and childGroups() recursively.

See also childGroups() and allKeys().

void QSettings::clear()

Removes all entries in the primary location associated to this QSettings object.

Entries in fallback locations are not removed.

If you only want to remove the entries in the current group(), use remove("") instead.

See also remove() and setFallbacksEnabled().

bool QSettings::contains(const QString &key) const

Returns true if there exists a setting called key; returns false otherwise.

If a group is set using beginGroup(), key is taken to be relative to that group.

Note that the Windows registry and INI files use case-insensitive keys, whereas the CFPreferences API on macOS and iOS uses case-sensitive keys. To avoid portability problems, see the Section and Key Syntax rules.

See also value() and setValue().

[static] QSettings::Format QSettings::defaultFormat()

Returns default file format used for storing settings for the QSettings(QObject *) constructor. If no default format is set, QSettings::NativeFormat is used.

This function was introduced in Qt 4.4.

See also setDefaultFormat() and format().

void QSettings::endArray()

Closes the array that was started using beginReadArray() or beginWriteArray().

See also beginReadArray() and beginWriteArray().

void QSettings::endGroup()

Resets the group to what it was before the corresponding beginGroup() call.

Example:

settings.beginGroup("alpha");
// settings.group() == "alpha"

settings.beginGroup("beta");
// settings.group() == "alpha/beta"

settings.endGroup();
// settings.group() == "alpha"

settings.endGroup();
// settings.group() == ""

See also beginGroup() and group().

[override virtual protected] bool QSettings::event(QEvent *event)

Reimplements: QObject::event(QEvent *e).

bool QSettings::fallbacksEnabled() const

Returns true if fallbacks are enabled; returns false otherwise.

By default, fallbacks are enabled.

See also setFallbacksEnabled().

QString QSettings::fileName() const

Returns the path where settings written using this QSettings object are stored.

On Windows, if the format is QSettings::NativeFormat, the return value is a system registry path, not a file path.

See also isWritable() and format().

QSettings::Format QSettings::format() const

Returns the format used for storing the settings.

This function was introduced in Qt 4.4.

See also defaultFormat(), fileName(), scope(), organizationName(), and applicationName().

QString QSettings::group() const

Returns the current group.

See also beginGroup() and endGroup().

QTextCodec *QSettings::iniCodec() const

Returns the codec that is used for accessing INI files. By default, no codec is used, so nullptr is returned.

This function was introduced in Qt 4.5.

See also setIniCodec().

bool QSettings::isAtomicSyncRequired() const

Returns true if QSettings is only allowed to perform atomic saving and reloading (synchronization) of the settings. Returns false if it is allowed to save the settings contents directly to the configuration file.

The default is true.

This function was introduced in Qt 5.10.

See also setAtomicSyncRequired() and QSaveFile.

bool QSettings::isWritable() const

Returns true if settings can be written using this QSettings object; returns false otherwise.

One reason why isWritable() might return false is if QSettings operates on a read-only file.

See also fileName(), status(), and sync().

QString QSettings::organizationName() const

Returns the organization name used for storing the settings.

This function was introduced in Qt 4.4.

See also QCoreApplication::organizationName(), format(), scope(), and applicationName().

[static] QSettings::Format QSettings::registerFormat(const QString &extension, QSettings::ReadFunc readFunc, QSettings::WriteFunc writeFunc, Qt::CaseSensitivity caseSensitivity = Qt::CaseSensitive)

Registers a custom storage format. On success, returns a special Format value that can then be passed to the QSettings constructor. On failure, returns InvalidFormat.

The extension is the file extension associated to the format (without the '.').

The readFunc and writeFunc parameters are pointers to functions that read and write a set of key/value pairs. The QIODevice parameter to the read and write functions is always opened in binary mode (i.e., without the QIODevice::Text flag).

The caseSensitivity parameter specifies whether keys are case sensitive or not. This makes a difference when looking up values using QSettings. The default is case sensitive.

By default, if you use one of the constructors that work in terms of an organization name and an application name, the file system locations used are the same as for IniFormat. Use setPath() to specify other locations.

Example:

bool readXmlFile(QIODevice &device, QSettings::SettingsMap &map);
bool writeXmlFile(QIODevice &device, const QSettings::SettingsMap &map);

int main(int argc, char *argv[])
{
    const QSettings::Format XmlFormat =
            QSettings::registerFormat("xml", readXmlFile, writeXmlFile);

    QSettings settings(XmlFormat, QSettings::UserScope, "MySoft",
                       "Star Runner");

    ...
}

Note: This function is thread-safe.

This function was introduced in Qt 4.1.

See also setPath().

void QSettings::remove(const QString &key)

Removes the setting key and any sub-settings of key.

Example:

QSettings settings;
settings.setValue("ape");
settings.setValue("monkey", 1);
settings.setValue("monkey/sea", 2);
settings.setValue("monkey/doe", 4);

settings.remove("monkey");
QStringList keys = settings.allKeys();
// keys: ["ape"]

Be aware that if one of the fallback locations contains a setting with the same key, that setting will be visible after calling remove().

If key is an empty string, all keys in the current group() are removed. For example:

QSettings settings;
settings.setValue("ape");
settings.setValue("monkey", 1);
settings.setValue("monkey/sea", 2);
settings.setValue("monkey/doe", 4);

settings.beginGroup("monkey");
settings.remove("");
settings.endGroup();

QStringList keys = settings.allKeys();
// keys: ["ape"]

Note that the Windows registry and INI files use case-insensitive keys, whereas the CFPreferences API on macOS and iOS uses case-sensitive keys. To avoid portability problems, see the Section and Key Syntax rules.

See also setValue(), value(), and contains().

QSettings::Scope QSettings::scope() const

Returns the scope used for storing the settings.

This function was introduced in Qt 4.4.

See also format(), organizationName(), and applicationName().

void QSettings::setArrayIndex(int i)

Sets the current array index to i. Calls to functions such as setValue(), value(), remove(), and contains() will operate on the array entry at that index.

You must call beginReadArray() or beginWriteArray() before you can call this function.

void QSettings::setAtomicSyncRequired(bool enable)

Configures whether QSettings is required to perform atomic saving and reloading (synchronization) of the settings. If the enable argument is true (the default), sync() will only perform synchronization operations that are atomic. If this is not possible, sync() will fail and status() will be an error condition.

Setting this property to false will allow QSettings to write directly to the configuration file and ignore any errors trying to lock it against other processes trying to write at the same time. Because of the potential for corruption, this option should be used with care, but is required in certain conditions, like a QSettings::IniFormat configuration file that exists in an otherwise non-writeable directory or NTFS Alternate Data Streams.

See QSaveFile for more information on the feature.

This function was introduced in Qt 5.10.

See also isAtomicSyncRequired() and QSaveFile.

[static] void QSettings::setDefaultFormat(QSettings::Format format)

Sets the default file format to the given format, which is used for storing settings for the QSettings(QObject *) constructor.

If no default format is set, QSettings::NativeFormat is used. See the documentation for the QSettings constructor you are using to see if that constructor will ignore this function.

This function was introduced in Qt 4.4.

See also defaultFormat() and format().

void QSettings::setFallbacksEnabled(bool b)

Sets whether fallbacks are enabled to b.

By default, fallbacks are enabled.

See also fallbacksEnabled().

void QSettings::setIniCodec(QTextCodec *codec)

Sets the codec for accessing INI files (including .conf files on Unix) to codec. The codec is used for decoding any data that is read from the INI file, and for encoding any data that is written to the file. By default, no codec is used, and non-ASCII characters are encoded using standard INI escape sequences.

This function was introduced in Qt 4.5.

See also iniCodec().

void QSettings::setIniCodec(const char *codecName)

This is an overloaded function.

Sets the codec for accessing INI files (including .conf files on Unix) to the QTextCodec for the encoding specified by codecName. Common values for codecName include "ISO 8859-1", "UTF-8", and "UTF-16". If the encoding isn't recognized, nothing happens.

This function was introduced in Qt 4.5.

See also QTextCodec::codecForName().

[static] void QSettings::setPath(QSettings::Format format, QSettings::Scope scope, const QString &path)

Sets the path used for storing settings for the given format and scope, to path. The format can be a custom format.

The table below summarizes the default values:

The default UserScope paths on Unix, macOS, and iOS ($HOME/.config or $HOME/Settings) can be overridden by the user by setting the XDG_CONFIG_HOME environment variable. The default SystemScope paths on Unix, macOS, and iOS (/etc/xdg) can be overridden when building the Qt library using the configure script's -sysconfdir flag (see QLibraryInfo for details).

Setting the NativeFormat paths on Windows, macOS, and iOS has no effect.

This function was introduced in Qt 4.1.

See also registerFormat().

void QSettings::setValue(const QString &key, const QVariant &value)

Sets the value of setting key to value. If the key already exists, the previous value is overwritten.

Note that the Windows registry and INI files use case-insensitive keys, whereas the CFPreferences API on macOS and iOS uses case-sensitive keys. To avoid portability problems, see the Section and Key Syntax rules.

Example:

QSettings settings;
settings.setValue("interval", 30);
settings.value("interval").toInt();     // returns 30

settings.setValue("interval", 6.55);
settings.value("interval").toDouble();  // returns 6.55

See also value(), remove(), and contains().

QSettings::Status QSettings::status() const

Returns a status code indicating the first error that was met by QSettings, or QSettings::NoError if no error occurred.

Be aware that QSettings delays performing some operations. For this reason, you might want to call sync() to ensure that the data stored in QSettings is written to disk before calling status().

See also sync().

void QSettings::sync()

Writes any unsaved changes to permanent storage, and reloads any settings that have been changed in the meantime by another application.

This function is called automatically from QSettings's destructor and by the event loop at regular intervals, so you normally don't need to call it yourself.

See also status().

QVariant QSettings::value(const QString &key, const QVariant &defaultValue = QVariant()) const

Returns the value for setting key. If the setting doesn't exist, returns defaultValue.

If no default value is specified, a default QVariant is returned.

Note that the Windows registry and INI files use case-insensitive keys, whereas the CFPreferences API on macOS and iOS uses case-sensitive keys. To avoid portability problems, see the Section and Key Syntax rules.

Example:

QSettings settings;
settings.setValue("animal/snake", 58);
settings.value("animal/snake", 1024).toInt();   // returns 58
settings.value("animal/zebra", 1024).toInt();   // returns 1024
settings.value("animal/zebra").toInt();         // returns 0

See also setValue(), contains(), and remove().