QMessageLogger Class

The QMessageLogger class generates log messages. More...

Header:	#include <QMessageLogger>
CMake:	find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core

List of all members, including inherited members

Public Types

CategoryFunction

Public Functions

	QMessageLogger()
	QMessageLogger(const char *file, int line, const char *function)
	QMessageLogger(const char *file, int line, const char *function, const char *category)
void	critical(const char *msg, ...) const
void	critical(const QLoggingCategory &cat, const char *msg, ...) const
void	critical(QMessageLogger::CategoryFunction catFunc, const char *msg, ...) const
QDebug	critical() const
QDebug	critical(const QLoggingCategory &cat) const
QDebug	critical(QMessageLogger::CategoryFunction catFunc) const
void	debug(const char *msg, ...) const
void	debug(const QLoggingCategory &cat, const char *msg, ...) const
void	debug(QMessageLogger::CategoryFunction catFunc, const char *msg, ...) const
QDebug	debug() const
QDebug	debug(const QLoggingCategory &cat) const
QDebug	debug(QMessageLogger::CategoryFunction catFunc) const
void	fatal(const char *msg, ...) const
`(since 6.5)` void	fatal(const QLoggingCategory &cat, const char *msg, ...) const
`(since 6.5)` void	fatal(QMessageLogger::CategoryFunction catFunc, const char *msg, ...) const
`(since 6.5)` QDebug	fatal() const
`(since 6.5)` QDebug	fatal(const QLoggingCategory &cat) const
`(since 6.5)` QDebug	fatal(QMessageLogger::CategoryFunction catFunc) const
void	info(const char *msg, ...) const
void	info(const QLoggingCategory &cat, const char *msg, ...) const
void	info(QMessageLogger::CategoryFunction catFunc, const char *msg, ...) const
QDebug	info() const
QDebug	info(const QLoggingCategory &cat) const
QDebug	info(QMessageLogger::CategoryFunction catFunc) const
void	warning(const char *msg, ...) const
void	warning(const QLoggingCategory &cat, const char *msg, ...) const
void	warning(QMessageLogger::CategoryFunction catFunc, const char *msg, ...) const
QDebug	warning() const
QDebug	warning(const QLoggingCategory &cat) const
QDebug	warning(QMessageLogger::CategoryFunction catFunc) const

Detailed Description

QMessageLogger is used to generate messages for the Qt logging framework. Usually one uses it through qDebug(), qInfo(), qWarning(), qCritical, or qFatal() functions, which are actually macros: For example qDebug() expands to QMessageLogger(__FILE__, __LINE__, Q_FUNC_INFO).debug() for debug builds, and QMessageLogger(0, 0, 0).debug() for release builds.

One example of direct use is to forward errors that stem from a scripting language, e.g. QML:

    void statusChanged(QQmlComponent::Status status) {
        if (status == QQmlComponent::Error) {
            for (const QQmlError &error: std::as_const(component->errors())) {
                const QByteArray file = error.url().toEncoded();
                QMessageLogger(file.constData(), error.line(), 0).debug() << error.description();
            }
        }
    }

See also QMessageLogContext, qDebug(), qInfo(), qWarning(), qCritical(), and qFatal().

Member Type Documentation

QMessageLogger::CategoryFunction

This is a typedef for a pointer to a function with the following signature:

    const QLoggingCategory &category();

The Q_DECLARE_LOGGING_CATEGORY macro generates a function declaration with this signature, and Q_LOGGING_CATEGORY generates its definition.

Member Function Documentation

`[constexpr]` QMessageLogger::QMessageLogger()

Constructs a default QMessageLogger. See the other constructors to specify context information.

`[constexpr]` QMessageLogger::QMessageLogger(const char **file, int line*, const char **function*)

Constructs a QMessageLogger to record log messages for file at line in function. The is equivalent to QMessageLogger(file, line, function, "default")

`[constexpr]` QMessageLogger::QMessageLogger(const char **file, int line*, const char **function*, const char **category*)

Constructs a QMessageLogger to record category messages for file at line in function.

void QMessageLogger::critical(const char **msg*, ...) const

Logs a critical message specified with format msg. Additional parameters, specified by msg, may be used.

See also qCritical().

void QMessageLogger::critical(const QLoggingCategory &cat, const char **msg*, ...) const

Logs a critical message specified with format msg for the context cat. Additional parameters, specified by msg, may be used.

See also qCCritical().

void QMessageLogger::critical(QMessageLogger::CategoryFunction catFunc, const char **msg*, ...) const

Logs a critical message specified with format msg for the context returned by catFunc. Additional parameters, specified by msg, may be used.

See also qCCritical().

QDebug QMessageLogger::critical() const

Logs a critical message using a QDebug stream

See also qCritical() and QDebug.

QDebug QMessageLogger::critical(const QLoggingCategory &cat) const

Logs a critical message into category cat using a QDebug stream.

See also qCCritical() and QDebug.

QDebug QMessageLogger::critical(QMessageLogger::CategoryFunction catFunc) const

Logs a critical message into category returned by catFunc using a QDebug stream.

See also qCCritical() and QDebug.

void QMessageLogger::debug(const char **msg*, ...) const

Logs a debug message specified with format msg. Additional parameters, specified by msg, may be used.

See also qDebug().

void QMessageLogger::debug(const QLoggingCategory &cat, const char **msg*, ...) const

Logs a debug message specified with format msg for the context cat. Additional parameters, specified by msg, may be used.

See also qCDebug().

void QMessageLogger::debug(QMessageLogger::CategoryFunction catFunc, const char **msg*, ...) const

Logs a debug message specified with format msg for the context returned by catFunc. Additional parameters, specified by msg, may be used.

See also qCDebug().

QDebug QMessageLogger::debug() const

Logs a debug message using a QDebug stream

See also qDebug() and QDebug.

QDebug QMessageLogger::debug(const QLoggingCategory &cat) const

Logs a debug message into category cat using a QDebug stream.

See also qCDebug() and QDebug.

QDebug QMessageLogger::debug(QMessageLogger::CategoryFunction catFunc) const

Logs a debug message into category returned by catFunc using a QDebug stream.

See also qCDebug() and QDebug.

`[noexcept]` void QMessageLogger::fatal(const char **msg*, ...) const

Logs a fatal message specified with format msg. Additional parameters, specified by msg, may be used.

See also qFatal().

`[noexcept, since 6.5]` void QMessageLogger::fatal(const QLoggingCategory &cat, const char **msg*, ...) const

Logs a fatal message specified with format msg for the context cat. Additional parameters, specified by msg, may be used.