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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
#include "qloggingcategory.h"
#include "qloggingcategory_p.h"
#include "qloggingregistry_p.h"
QT_BEGIN_NAMESPACE
/*!
\class QLoggingCategory
\inmodule QtCore
\since 5.2
\threadsafe
\brief The QLoggingCategory class represents a category, or 'area' in the
logging infrastructure.
QLoggingCategory represents a certain logging category - identified by a
string - at runtime. A category can be configured to enable or disable
logging of messages per message type. An exception are fatal messages,
which are always enabled.
To check whether a message type is enabled or not, use one of these methods:
\l isDebugEnabled(), \l isInfoEnabled(), \l isWarningEnabled(), and
\l isCriticalEnabled().
All objects are meant to be configured by a common registry, as described in
\l{Configuring Categories}. Different objects can also represent the same
category. Therefore, it's \b{not} recommended to export objects across
module boundaries, to manipulate the objects directly, or to inherit from
QLoggingCategory.
\section1 Creating Category Objects
The Q_DECLARE_LOGGING_CATEGORY() and Q_LOGGING_CATEGORY() macros
conveniently declare and create QLoggingCategory objects:
\snippet qloggingcategory/main.cpp 1
There is also the Q_DECLARE_EXPORTED_LOGGING_CATEGORY() macro in
order to use a logging category across library boundaries.
Category names are free text; to configure categories using \l{Logging Rules}, their
names should follow this convention:
\list
\li Use letters and numbers only.
\li Use dots to further structure categories into common areas.
\li Avoid the category names: \c{debug}, \c{info}, \c{warning}, and \c{critical}.
\li Category names with the \c{qt} prefix are solely reserved for Qt modules.
\endlist
QLoggingCategory objects that are implicitly defined by Q_LOGGING_CATEGORY()
are created on first use, in a thread-safe manner.
\section1 Checking Category Configuration
QLoggingCategory provides \l isDebugEnabled(), \l isInfoEnabled(),
\l isWarningEnabled(), \l isCriticalEnabled(), as well as \l isEnabled()
to check whether messages for the given message type should be logged.
The qCDebug(), qCWarning(), and qCCritical() macros prevent arguments from
being evaluated if the respective message types are not enabled for the
category, so explicit checking is not needed:
\snippet qloggingcategory/main.cpp 4
\section1 Default Category Configuration
Both the QLoggingCategory constructor and the Q_LOGGING_CATEGORY() macro
accept an optional QtMsgType argument, which disables all message types with
a lower severity. That is, a category declared with
\snippet qloggingcategory/main.cpp 5
logs messages of type \c QtWarningMsg, \c QtCriticalMsg, \c QtFatalMsg, but
ignores messages of type \c QtDebugMsg and \c QtInfoMsg.
If no argument is passed, all messages are logged. Only Qt internal categories
which start with \c{qt} are handled differently: For these, only messages of type
\c QtInfoMsg, \c QtWarningMsg, \c QtCriticalMsg, and \c QFatalMsg are logged by default.
\note Logging categories are not affected by your C++ build configuration.
That is, whether messages are printed does not change depending on whether
the code is compiled with debug symbols ('Debug Build'), optimizations
('Release Build'), or some other combination.
\section1 Configuring Categories
You can override the default configuration for categories either by setting
logging rules, or by installing a custom filter.
\section2 Logging Rules
Logging rules let you enable or disable logging for categories in a flexible
way. Rules are specified in text, where every line must have the format:
\snippet code/src_corelib_io_qloggingcategory.cpp 0
\c <category> is the name of the category, potentially with \c{*} as a
wildcard symbol for the first or last character; or at both positions.
The optional \c <type> must be \c debug, \c info, \c warning, or \c critical.
Lines that don't fit this scheme are ignored.
Rules are evaluated in text order, from first to last. That is, if two rules
apply to a category/type, the rule that comes later is applied.
Rules can be set via \l setFilterRules():
\snippet code/src_corelib_io_qloggingcategory.cpp 1
Logging rules are automatically loaded from the \c [Rules] section in a logging
configuration file. These configuration files are looked up in the QtProject
configuration directory, or explicitly set in a \c QT_LOGGING_CONF environment
variable:
\snippet code/src_corelib_io_qloggingcategory.cpp 2
Logging rules can also be specified in a \c QT_LOGGING_RULES environment variable;
multiple rules can also be separated by semicolons:
\snippet code/src_corelib_io_qloggingcategory.cpp 3
Rules set by \l setFilterRules() take precedence over rules specified in the
QtProject configuration directory. In turn, these rules can be overwritten by those
from the configuration file specified by \c QT_LOGGING_CONF, and those set by
\c QT_LOGGING_RULES.
The order of evaluation is as follows:
\list 1
\li [QLibraryInfo::DataPath]/qtlogging.ini
\li QtProject/qtlogging.ini
\li \l setFilterRules()
\li \c QT_LOGGING_CONF
\li \c QT_LOGGING_RULES
\endlist
The \c QtProject/qtlogging.ini file is looked up in all directories returned
by QStandardPaths::GenericConfigLocation.
Set the \c QT_LOGGING_DEBUG environment variable to find out where your logging
rules are loaded from.
\section2 Installing a Custom Filter
As a lower-level alternative to the text rules, you can also implement a
custom filter via \l installFilter(). All filter rules are ignored in this
case.
\section1 Printing the Category
Use the \c %{category} placeholder to print the category in the default
message handler:
\snippet qloggingcategory/main.cpp 3
*/
/*!
Constructs a QLoggingCategory object with the provided \a category name,
and enables all messages with types at least as verbose as \a enableForLevel,
which defaults to QtDebugMsg (which enables all categories).
If \a category is \nullptr, the category name \c "default" is used.
\note \a category must be kept valid during the lifetime of this object.
Using a string literal for it is the usual way to achieve this.
\since 5.4
*/
QLoggingCategory::QLoggingCategory(const char *category, QtMsgType enableForLevel)
: QLoggingCategory(UnregisteredInitialization{},
category ? category : QLoggingRegistry::defaultCategoryName)
{
if (QLoggingRegistry *reg = QLoggingRegistry::instance())
reg->registerCategory(this, enableForLevel);
}
/*!
Destroys a QLoggingCategory object.
*/
QLoggingCategory::~QLoggingCategory()
{
// Note: this destructor is never called for the defaultCategory(), so it
// is always registered. If we ever need to free memory, make
// QLoggingRegistry do it.
if (QLoggingRegistry *reg = QLoggingRegistry::instance())
reg->unregisterCategory(this);
}
/*!
\fn const char *QLoggingCategory::categoryName() const
Returns the name of the category.
*/
/*!
\fn bool QLoggingCategory::isDebugEnabled() const
Returns \c true if debug messages should be shown for this category;
\c false otherwise.
\note The \l qCDebug() macro already does this check before running any
code. However, calling this method may be useful to avoid the
expensive generation of data for debug output only.
*/
/*!
\fn bool QLoggingCategory::isInfoEnabled() const
Returns \c true if informational messages should be shown for this category;
\c false otherwise.
\note The \l qCInfo() macro already does this check before executing any
code. However, calling this method may be useful to avoid the
expensive generation of data for debug output only.
\since 5.5
*/
/*!
\fn bool QLoggingCategory::isWarningEnabled() const
Returns \c true if warning messages should be shown for this category;
\c false otherwise.
\note The \l qCWarning() macro already does this check before executing any
code. However, calling this method may be useful to avoid the
expensive generation of data for debug output only.
*/
/*!
\fn bool QLoggingCategory::isCriticalEnabled() const
Returns \c true if critical messages should be shown for this category;
\c false otherwise.
\note The \l qCCritical() macro already does this check before executing any
code. However, calling this method may be useful to avoid the
expensive generation of data for debug output only.
*/
/*!
Returns \c true if a message of type \a msgtype for the category should be
shown; \c false otherwise.
*/
bool QLoggingCategory::isEnabled(QtMsgType msgtype) const
{
switch (msgtype) {
case QtDebugMsg: return isDebugEnabled();
case QtInfoMsg: return isInfoEnabled();
case QtWarningMsg: return isWarningEnabled();
case QtCriticalMsg: return isCriticalEnabled();
case QtFatalMsg: return true;
}
return false;
}
/*!
Changes the message type \a type for the category to \a enable.
This method is meant for use only from inside a filter installed with
\l installFilter(). For an overview on how to configure categories globally,
see \l {Configuring Categories}.
\note \c QtFatalMsg cannot be changed; it will always remain \c true.
*/
void QLoggingCategory::setEnabled(QtMsgType type, bool enable)
{
switch (type) {
case QtDebugMsg: bools.enabledDebug.storeRelaxed(enable); break;
case QtInfoMsg: bools.enabledInfo.storeRelaxed(enable); break;
case QtWarningMsg: bools.enabledWarning.storeRelaxed(enable); break;
case QtCriticalMsg: bools.enabledCritical.storeRelaxed(enable); break;
case QtFatalMsg: break;
}
}
/*!
\fn QLoggingCategory &QLoggingCategory::operator()()
Returns the object itself. This allows for both: a QLoggingCategory variable, and
a factory method that returns a QLoggingCategory, to be used in \l qCDebug(),
\l qCWarning(), \l qCCritical(), or \l qCFatal() macros.
*/
/*!
\fn const QLoggingCategory &QLoggingCategory::operator()() const
Returns the object itself. This allows for both: a QLoggingCategory variable, and
a factory method that returns a QLoggingCategory, to be used in \l qCDebug(),
\l qCWarning(), \l qCCritical(), or \l qCFatal() macros.
*/
/*!
Returns a pointer to the global category \c "default" that is used, for
example, by qDebug(), qInfo(), qWarning(), qCritical(), or qFatal().
\note The pointer returned may be null during destruction of static objects.
Also, don't \c delete this pointer, as ownership of the category isn't transferred.
*/
QLoggingCategory *QLoggingCategory::defaultCategory()
{
return QLoggingRegistry::defaultCategory();
}
/*!
\typedef QLoggingCategory::CategoryFilter
This is a typedef for a pointer to a function with the following signature:
\snippet qloggingcategory/main.cpp 20
A function with this signature can be installed with \l installFilter().
*/
/*!
\brief Take control of how logging categories are configured.
Installs a function \a filter that is used to determine which categories and
message types should be enabled. If \a filter is \nullptr, the default
message filter is reinstated. Returns a pointer to the previously-installed
filter.
Every QLoggingCategory object that already exists is passed to the filter
before \c installFilter() returns, and the filter is free to change each
category's configuration with \l setEnabled(). Any category it doesn't
change will retain the configuration it was given by the prior filter, so
the new filter does not need to delegate to the prior filter during this
initial pass over existing categories.
Any new categories added later will be passed to the new filter; a filter
that only aims to tweak the configuration of a select few categories, rather
than completely overriding the logging policy, can first pass the new
category to the prior filter, to give it its standard configuration, and
then tweak that as desired, if it is one of the categories of specific
interest to the filter. The code that installs the new filter can record the
return from \c installFilter() for the filter to use in such later calls.
When you define your filter, note that it can be called from different threads; but never
concurrently. This filter cannot call any static functions from QLoggingCategory.
Example:
\snippet qloggingcategory/main.cpp 21
installed (in \c{main()}, for example) by
\snippet qloggingcategory/main.cpp 22
Alternatively, you can configure the default filter via \l setFilterRules().
*/
QLoggingCategory::CategoryFilter
QLoggingCategory::installFilter(QLoggingCategory::CategoryFilter filter)
{
return QLoggingRegistry::instance()->installFilter(filter);
}
/*!
Configures which categories and message types should be enabled through a
set of \a rules.
Example:
\snippet qloggingcategory/main.cpp 2
\note The rules might be ignored if a custom category filter is installed
with \l installFilter(), or if the user has defined the \c QT_LOGGING_CONF
or the \c QT_LOGGING_RULES environment variable.
*/
void QLoggingCategory::setFilterRules(const QString &rules)
{
QLoggingRegistry::instance()->setApiRules(rules);
}
/*!
\macro qCDebug(category)
\relates QLoggingCategory
\threadsafe
\since 5.2
Returns an output stream for debug messages in the logging category,
\a category.
The macro expands to code that checks whether
\l QLoggingCategory::isDebugEnabled() evaluates to \c true.
If so, the stream arguments are processed and sent to the message handler.
Example:
\snippet qloggingcategory/main.cpp 10
\note Arguments aren't processed if the debug output for that \a category is not
enabled, so don't rely on any side effects.
\sa QDebug::qDebug()
*/
/*!
\macro qCDebug(category, const char *message, ...)
\relates QLoggingCategory
\threadsafe
\since 5.3
Logs a debug message, \a message, in the logging category, \a category.
\a message may contain place holders to be replaced by additional arguments,
similar to the C printf() function.
Example:
\snippet qloggingcategory/main.cpp 13
\note Arguments aren't processed if the debug output for that \a category is not
enabled, so don't rely on any side effects.
\sa qDebug(const char *, ...)
*/
/*!
\macro qCInfo(category)
\relates QLoggingCategory
\threadsafe
\since 5.5
Returns an output stream for informational messages in the logging category,
\a category.
The macro expands to code that checks whether
\l QLoggingCategory::isInfoEnabled() evaluates to \c true.
If so, the stream arguments are processed and sent to the message handler.
Example:
\snippet qloggingcategory/main.cpp qcinfo_stream
\note If the debug output for a particular category isn't enabled, arguments
won't be processed, so don't rely on any side effects.
\sa QDebug::qInfo()
*/
/*!
\macro qCInfo(category, const char *message, ...)
\relates QLoggingCategory
\threadsafe
\since 5.5
Logs an informational message, \a message, in the logging category, \a category.
\a message may contain place holders to be replaced by additional arguments,
similar to the C printf() function.
Example:
\snippet qloggingcategory/main.cpp qcinfo_printf
\note If the debug output for a particular category isn't enabled, arguments
won't be processed, so don't rely on any side effects.
\sa qInfo(const char *, ...)
*/
/*!
\macro qCWarning(category)
\relates QLoggingCategory
\threadsafe
\since 5.2
Returns an output stream for warning messages in the logging category,
\a category.
The macro expands to code that checks whether
\l QLoggingCategory::isWarningEnabled() evaluates to \c true.
If so, the stream arguments are processed and sent to the message handler.
Example:
\snippet qloggingcategory/main.cpp 11
\note If the warning output for a particular category isn't enabled, arguments
won't be processed, so don't rely on any side effects.
\sa QDebug::qWarning()
*/
/*!
\macro qCWarning(category, const char *message, ...)
\relates QLoggingCategory
\threadsafe
\since 5.3
Logs a warning message, \a message, in the logging category, \a category.
\a message may contain place holders to be replaced by additional arguments,
similar to the C printf() function.
Example:
\snippet qloggingcategory/main.cpp 14
\note If the warning output for a particular category isn't enabled, arguments
won't be processed, so don't rely on any side effects.
\sa qWarning(const char *, ...)
*/
/*!
\macro qCCritical(category)
\relates QLoggingCategory
\threadsafe
\since 5.2
Returns an output stream for critical messages in the logging category,
\a category.
The macro expands to code that checks whether
\l QLoggingCategory::isCriticalEnabled() evaluates to \c true.
If so, the stream arguments are processed and sent to the message handler.
Example:
\snippet qloggingcategory/main.cpp 12
\note If the critical output for a particular category isn't enabled, arguments
won't be processed, so don't rely on any side effects.
\sa QDebug::qCritical()
*/
/*!
\macro qCCritical(category, const char *message, ...)
\relates QLoggingCategory
\threadsafe
\since 5.3
Logs a critical message, \a message, in the logging category, \a category.
\a message may contain place holders to be replaced by additional arguments,
similar to the C printf() function.
Example:
\snippet qloggingcategory/main.cpp 15
\note If the critical output for a particular category isn't enabled, arguments
won't be processed, so don't rely on any side effects.
\sa qCritical(const char *, ...)
*/
/*!
\macro qCFatal(category)
\relates QLoggingCategory
\since 6.5
Returns an output stream for fatal messages in the logging category,
\a category.
If you are using the \b{default message handler}, the returned stream will abort
to create a core dump. On Windows, for debug builds, this function will
report a \c _CRT_ERROR enabling you to connect a debugger to the application.
Example:
\snippet qloggingcategory/main.cpp 16
\sa QDebug::qFatal()
*/
/*!
\macro qCFatal(category, const char *message, ...)
\relates QLoggingCategory
\since 6.5
Logs a fatal message, \a message, in the logging category, \a category.
\a message may contain place holders to be replaced by additional arguments,
similar to the C printf() function.
Example:
\snippet qloggingcategory/main.cpp 17
If you are using the \b{default message handler}, this function will abort
to create a core dump. On Windows, for debug builds, this function will
report a \c _CRT_ERROR enabling you to connect a debugger to the application.
\sa qFatal(const char *, ...)
*/
/*!
\macro Q_DECLARE_LOGGING_CATEGORY(name)
\sa Q_LOGGING_CATEGORY(), Q_DECLARE_EXPORTED_LOGGING_CATEGORY()
\relates QLoggingCategory
\since 5.2
Declares a logging category \a 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.
*/
/*!
\macro Q_DECLARE_EXPORTED_LOGGING_CATEGORY(name, EXPORT_MACRO)
\sa Q_LOGGING_CATEGORY(), Q_DECLARE_LOGGING_CATEGORY()
\relates QLoggingCategory
\since 6.5
Declares a logging category \a name. The macro can be used to declare
a common logging category shared in different parts of the program.
This works exactly like Q_DECLARE_LOGGING_CATEGORY(). However,
the logging category declared by this macro is additionally
qualified with \a EXPORT_MACRO. This is useful if the logging
category needs to be exported from a dynamic library.
For example:
\code
Q_DECLARE_EXPORTED_LOGGING_CATEGORY(lcCore, LIB_EXPORT_MACRO)
\endcode
This macro must be used outside of a class or function.
*/
/*!
\macro Q_LOGGING_CATEGORY(name, string)
\sa Q_DECLARE_LOGGING_CATEGORY(), Q_DECLARE_EXPORTED_LOGGING_CATEGORY()
\relates QLoggingCategory
\since 5.2
Defines a logging category \a name, and makes it configurable under the
\a 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.
*/
/*!
\macro Q_LOGGING_CATEGORY(name, string, msgType)
\sa Q_DECLARE_LOGGING_CATEGORY()
\relates QLoggingCategory
\since 5.4
Defines a logging category \a name, and makes it configurable under the
\a string identifier. By default, messages of QtMsgType \a 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.
*/
/*!
\macro Q_STATIC_LOGGING_CATEGORY(name, string)
\sa Q_LOGGING_CATEGORY()
\relates QLoggingCategory
\since 6.9
Defines a static logging category \a name, and makes it configurable under
the \a string identifier. By default, all message types are enabled.
The logging category is created using the \c static qualifier so that you
can only access it in the same translation unit. This avoids accidental
symbol clashes.
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.
*/
/*!
\macro Q_STATIC_LOGGING_CATEGORY(name, string, msgType)
\sa Q_LOGGING_CATEGORY()
\relates QLoggingCategory
\since 6.9
Defines a static logging category \a name, and makes it configurable under
the \a string identifier. By default, messages of QtMsgType \a msgType and
more severe are enabled, types with a lower severity are disabled.
The logging category is created using the \c static qualifier so that you
can only access it in the same translation unit. This avoids accidental
symbol clashes.
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.
*/
QT_END_NAMESPACE