QLoggingCategory Class

 // in a header
 Q_DECLARE_LOGGING_CATEGORY(driverUsb)

 // in one source file
 Q_LOGGING_CATEGORY(driverUsb, "driver.usb")

     // usbEntries() will only be called if driverUsb category is enabled
     qCDebug(driverUsb) << "devices: " << usbEntries();

 Q_LOGGING_CATEGORY(driverUsbEvents, "driver.usb.events", QtWarningMsg)

     <category>[.<type>] = true|false

     QLoggingCategory::setFilterRules("*.debug=false\n"
                                      "driver.usb.debug=true");

     [Rules]
     *.debug=false
     driver.usb.debug=true

     QT_LOGGING_RULES="*.debug=false;driver.usb.debug=true"

     qSetMessagePattern("%{category} %{message}");

 void myCategoryFilter(QLoggingCategory *);

 QLoggingCategory::CategoryFilter oldCategoryFilter;

 void myCategoryFilter(QLoggingCategory *category)
 {
     // configure driver.usb category here, otherwise forward to to default filter.
     if (qstrcmp(category->categoryName(), "driver.usb") == 0)
         category->setEnabled(QtDebugMsg, true);
     else
         oldCategoryFilter(category);
 }

     QLoggingCategory::setFilterRules(QStringLiteral("driver.usb.debug=true"));

Macro Documentation

Q_DECLARE_LOGGING_CATEGORY(name)

Declares a logging category name. The macro can be used to declare a common logging category shared in different parts of the program.

This macro must be used outside of a class or method.

This function was introduced in Qt 5.2.

See also Q_LOGGING_CATEGORY().

Q_LOGGING_CATEGORY(name, string, msgType)

Defines a logging category name, and makes it configurable under the string identifier. By default, messages of QtMsgType msgType and more severe are enabled, types with a lower severity are disabled.

Only one translation unit in a library or executable can define a category with a specific name. The implicitly-defined QLoggingCategory object is created on first use, in a thread-safe manner.

This macro must be used outside of a class or method. It is only defined if variadic macros are supported.

This function was introduced in Qt 5.4.

See also Q_DECLARE_LOGGING_CATEGORY().

Q_LOGGING_CATEGORY(name, string)

Defines a logging category name, and makes it configurable under the string identifier. By default, all message types are enabled.

Only one translation unit in a library or executable can define a category with a specific name. The implicitly-defined QLoggingCategory object is created on first use, in a thread-safe manner.

This macro must be used outside of a class or method.

This function was introduced in Qt 5.2.

See also Q_DECLARE_LOGGING_CATEGORY().

qCCritical(category, const char *message, ...)

Logs a critical message, message, in the logging category, category. message may contain place holders to be replaced by additional arguments, similar to the C printf() function.

Example:

     QLoggingCategory category("driver.usb");
     qCCritical(category, "a critical message logged into category %s", category.categoryName());

This function was introduced in Qt 5.3.

See also qCritical().

qCCritical(category)

Returns an output stream for critical messages in the logging category, category.

The macro expands to code that checks whether QLoggingCategory::isCriticalEnabled() evaluates to true. If so, the stream arguments are processed and sent to the message handler.

Example:

     QLoggingCategory category("driver.usb");
     qCCritical(category) << "a critical message";

This function was introduced in Qt 5.2.

See also qCritical().

qCDebug(category, const char *message, ...)

Logs a debug message, message, in the logging category, category. message may contain place holders to be replaced by additional arguments, similar to the C printf() function.

Example:

     QLoggingCategory category("driver.usb");
     qCDebug(category, "a debug message logged into category %s", category.categoryName());

This function was introduced in Qt 5.3.

See also qDebug().

qCDebug(category)

Returns an output stream for debug messages in the logging category, category.

The macro expands to code that checks whether QLoggingCategory::isDebugEnabled() evaluates to true. If so, the stream arguments are processed and sent to the message handler.

Example:

     QLoggingCategory category("driver.usb");
     qCDebug(category) << "a debug message";

This function was introduced in Qt 5.2.

See also qDebug().

qCInfo(category, const char *message, ...)

Logs an informational message, message, in the logging category, category. message may contain place holders to be replaced by additional arguments, similar to the C printf() function.

Example:

     QLoggingCategory category("driver.usb");
     qCInfo(category, "an informational message logged into category %s", category.categoryName());

This function was introduced in Qt 5.5.

See also qInfo().

qCInfo(category)

Returns an output stream for informational messages in the logging category, category.

The macro expands to code that checks whether QLoggingCategory::isInfoEnabled() evaluates to true. If so, the stream arguments are processed and sent to the message handler.

Example:

     QLoggingCategory category("driver.usb");
     qCInfo(category) << "an informational message";

This function was introduced in Qt 5.5.

See also qInfo().

qCWarning(category, const char *message, ...)

Logs a warning message, message, in the logging category, category. message may contain place holders to be replaced by additional arguments, similar to the C printf() function.

Example:

     QLoggingCategory category("driver.usb");
     qCWarning(category, "a warning message logged into category %s", category.categoryName());

This function was introduced in Qt 5.3.

See also qWarning().

qCWarning(category)

Returns an output stream for warning messages in the logging category, category.

The macro expands to code that checks whether QLoggingCategory::isWarningEnabled() evaluates to true. If so, the stream arguments are processed and sent to the message handler.

Example:

     QLoggingCategory category("driver.usb");
     qCWarning(category) << "a warning message";

This function was introduced in Qt 5.2.

See also qWarning().