QDebug Class

The QDebug class provides an output stream for debugging information. More…

List of all members, including inherited members

Public Functions

Static Public Members

Detailed Description

QDebug is used to write human-readable diagnostics. Obtain a stream from qDebug(), qInfo(), qWarning() or qCritical() and write values to it with <<. The message is emitted when the stream, and every copy of it, is destroyed, so a statement such as

qDebug() << "value:" << 42 << QString("text");

produces one message, value: 42 "text". Spaces are inserted between values unless disabled with nospace(), and strings are quoted unless disabled with noquote().

A message is written to stderr followed by a newline, in the format set with qSetMessagePattern(), unless a handler was installed with qInstallMessageHandler(). That handler then receives the message type (QtDebugMsg, QtInfoMsg, QtWarningMsg, QtCriticalMsg or QtFatalMsg), a QMessageLogContext and the text instead. A QtFatalMsg message aborts the process after it is handled.

The same functions also have printf-style forms, such as qDebug("count: %d", n), and qFatal() takes a format string. A QLoggingCategory selects which messages are written; see qCDebug().

See also QMessageLogger, QMessageLogContext, QDebugStateSaver and QLoggingCategory.

Differences from Qt

Member Function Documentation

[explicit] QDebug::QDebug(QtMsgType type)

Constructs a debug stream that emits a message of the given type when it is destroyed.

[explicit] QDebug::QDebug(QString *string)

Constructs a debug stream that appends its text to string when it is destroyed, instead of emitting a message. A space written after the last value is kept.

[explicit] QDebug::QDebug(QIODevice *device)

Constructs a debug stream that writes its text to device, as UTF-8, when it is destroyed, instead of emitting a message. A space written after the last value is kept.

QDebug::QDebug(const QDebug &)

Constructs a copy of another stream. The copies share one buffer, and the message is emitted when the last copy is destroyed.

QDebug::~QDebug()

Destroys the stream. If this is the last copy of the stream, the accumulated message is emitted, with a trailing space removed, and for QtFatalMsg the process is aborted. A stream for a QString or a QIODevice writes its text there instead.

bool QDebug::autoInsertSpaces() const

Returns true if spaces are inserted between values automatically.

See also setAutoInsertSpaces(), space() and nospace().

QDebug & QDebug::maybeQuote(char c = '"')

Writes the character c to the stream if quoting is enabled, and returns a reference to the stream.

See also quote() and noquote().

QDebug & QDebug::maybeSpace()

Writes a space character to the stream if spaces are enabled, and returns a reference to the stream.

See also space() and nospace().

QDebug & QDebug::noquote()

Disables quoting of strings and characters, and returns a reference to the stream. Strings are then written without escaping.

See also quote() and maybeQuote().

QDebug & QDebug::nospace()

Disables the automatic insertion of spaces between values, and returns a reference to the stream.

See also space() and maybeSpace().

QDebug & QDebug::operator<<(bool v)

Writes the boolean value v to the debug stream as true or false, and returns a reference to the stream.

QDebug & QDebug::operator<<(char v)

This is an overloaded function.

Writes the character v to the debug stream, in single quotes if quoting is enabled.

QDebug & QDebug::operator<<(signed char v)

This is an overloaded function.

Writes the signed character v to the debug stream as a number.

QDebug & QDebug::operator<<(unsigned char v)

This is an overloaded function.

Writes the unsigned character v to the debug stream as a number.

QDebug & QDebug::operator<<(short v)

This is an overloaded function.

Writes the short integer v to the debug stream.

QDebug & QDebug::operator<<(unsigned short v)

This is an overloaded function.

Writes the unsigned short integer v to the debug stream.

QDebug & QDebug::operator<<(int v)

This is an overloaded function.

Writes the integer v to the debug stream.

QDebug & QDebug::operator<<(unsigned int v)

This is an overloaded function.

Writes the unsigned integer v to the debug stream.

QDebug & QDebug::operator<<(long v)

This is an overloaded function.

Writes the long integer v to the debug stream.

QDebug & QDebug::operator<<(unsigned long v)

This is an overloaded function.

Writes the unsigned long integer v to the debug stream.

QDebug & QDebug::operator<<(long long v)

This is an overloaded function.

Writes the long long integer v to the debug stream.

QDebug & QDebug::operator<<(unsigned long long v)

This is an overloaded function.

Writes the unsigned long long integer v to the debug stream.

QDebug & QDebug::operator<<(float v)

This is an overloaded function.

Writes the float v to the debug stream, using the shortest representation that reads back unchanged.

QDebug & QDebug::operator<<(double v)

This is an overloaded function.

Writes the double v to the debug stream, using the shortest representation that reads back unchanged.

QDebug & QDebug::operator<<(const char *v)

This is an overloaded function.

Writes the zero-terminated string v to the debug stream, without quotes or escaping. A null pointer is written as (null).

QDebug & QDebug::operator<<(const std::string &v)

This is an overloaded function.

Writes the string v to the debug stream, without quotes or escaping.

QDebug & QDebug::operator<<(const void *p)

This is an overloaded function.

Writes the pointer p to the debug stream as a hexadecimal address.

QDebug & QDebug::operator<<(std::nullptr_t)

This is an overloaded function.

Writes (nullptr) to the debug stream.

QDebug & QDebug::operator<<(QChar c)

This is an overloaded function.

Writes the character c to the debug stream as a one-character string.

QDebug & QDebug::operator<<(const QString &v)

This is an overloaded function.

Writes the string v to the debug stream, in double quotes and with special characters escaped if quoting is enabled.

See also quote() and noquote().

QDebug & QDebug::operator<<(QLatin1StringView v)

This is an overloaded function.

Writes the Latin-1 string v to the debug stream, as for a QString.

QDebug & QDebug::operator<<(QStringView v)

Writes the string view v to the debug stream, quoted and escaped like a QString, and returns a reference to the stream.

This function was introduced in 5.10.

QDebug & QDebug::operator<<(const QByteArray &v)

This is an overloaded function.

Writes the byte array v to the debug stream, in double quotes and with special characters escaped if quoting is enabled.

QDebug & QDebug::operator<<(const QObject *o)

This is an overloaded function.

Writes the object o to the debug stream as its address and, if set, its object name, for example QObject(0x1234, name = "x"). A null pointer is written as QObject(0x0).

QDebug & QDebug::operator<<(QTextStreamFunction f)

Applies the QTextStream manipulator f, such as Qt::hex, Qt::showbase, Qt::fixed or Qt::endl, and returns a reference to the stream. The settings change how later numbers are written:

qDebug() << Qt::hex << Qt::showbase << 255 << Qt::dec << 255; // 0xff 255

This function was introduced in 5.4.

QDebug & QDebug::operator<<(const QTextStreamManipulator &m)

Applies the manipulator m, made by qSetFieldWidth(), qSetPadChar() or qSetRealNumberPrecision(), and returns a reference to the stream.

This function was introduced in 5.4.

QDebug & QDebug::operator=(const QDebug &)

Assigns another stream to this stream and returns a reference to this stream. The two streams then share one buffer.

QDebug & QDebug::quote()

Enables quoting of strings and characters, and returns a reference to the stream. This is the default.

See also noquote() and maybeQuote().

bool QDebug::quoteStrings() const

Returns true if strings, characters and byte arrays are written in quotes; otherwise returns false.

This function was introduced in 6.10.

See also setQuoteStrings(), quote() and noquote().

QDebug & QDebug::resetFormat()

Restores the default formatting: automatic spaces, quoting and verbosity 2. Returns a reference to the stream.

This function was introduced in 5.4.

See also space(), quote() and setVerbosity().

void QDebug::setAutoInsertSpaces(bool b)

Sets whether spaces are inserted between values automatically to b.

See also autoInsertSpaces(), space() and nospace().

void QDebug::setQuoteStrings(bool b)

Turns the quoting of strings, characters and byte arrays on if b is true and off otherwise.

This function was introduced in 6.10.

See also quoteStrings(), quote() and noquote().

void QDebug::setVerbosity(int verbosityLevel)

Sets the verbosity of the stream to verbosityLevel, which is clamped to the range 0 to 7. Streaming operators may use it to decide how much detail to write.

This function was introduced in 5.6.

See also verbosity().

QDebug & QDebug::space()

Writes a space character after each value written to the stream, and returns a reference to the stream. This is the default.

See also nospace() and maybeSpace().

void QDebug::swap(QDebug &other)

Swaps this stream with other.

This function was introduced in 5.0.

template <typename T>[static] QByteArray QDebug::toBytes(const T &object)

Returns object written to a debug stream, as UTF-8 encoded bytes.

This function was introduced in 6.9.

See also toString().

template <typename T>[static] QString QDebug::toString(const T &object)

Returns object written to a debug stream, as a string. The stream does not insert spaces, so the result is what qDebug().nospace() would print.

This function was introduced in 6.0.

See also toBytes().

int QDebug::verbosity() const

Returns the verbosity of the stream, from 0 (least verbose) to 7 (most verbose). The default is 2.

This function was introduced in 5.6.

See also setVerbosity().

QDebug & QDebug::verbosity(int verbosityLevel)

This is an overloaded function.

Sets the verbosity of the stream to verbosityLevel and returns a reference to the stream.

This function was introduced in 5.13.