QDebug Class

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

Header: #include <QDebug>

Public Functions

QDebug(QIODevice * device)
QDebug(QString * string)
QDebug(QtMsgType type)
QDebug(const QDebug & other)
~QDebug()
QDebug & maybeSpace()
QDebug & nospace()
QDebug & space()
QDebug & operator<<(QChar t)
QDebug & operator<<(bool t)
QDebug & operator<<(char t)
QDebug & operator<<(signed short i)
QDebug & operator<<(unsigned short i)
QDebug & operator<<(signed int i)
QDebug & operator<<(unsigned int i)
QDebug & operator<<(signed long l)
QDebug & operator<<(unsigned long l)
QDebug & operator<<(qint64 i)
QDebug & operator<<(quint64 i)
QDebug & operator<<(float f)
QDebug & operator<<(double f)
QDebug & operator<<(const char * s)
QDebug & operator<<(const QString & s)
QDebug & operator<<(const QStringRef & s)
QDebug & operator<<(const QLatin1String & s)
QDebug & operator<<(const QByteArray & b)
QDebug & operator<<(const void * p)
QDebug & operator=(const QDebug & other)

Detailed Description

The QDebug class provides an output stream for debugging information.

QDebug is used whenever the developer needs to write out debugging or tracing information to a device, file, string or console.

Basic Use

In the common case, it is useful to call the qDebug() function to obtain a default QDebug object to use for writing debugging information.

    qDebug() << "Date:" << QDate::currentDate();
    qDebug() << "Types:" << QString("String") << QChar('x') << QRect(0, 10, 50, 40);
    qDebug() << "Custom coordinate type:" << coordinate;

This constructs a QDebug object using the constructor that accepts a QtMsgType value of QtDebugMsg. Similarly, the qWarning(), qCritical() and qFatal() functions also return QDebug objects for the corresponding message types.

The class also provides several constructors for other situations, including a constructor that accepts a QFile or any other QIODevice subclass that is used to write debugging information to files and other devices. The constructor that accepts a QString is used to write to a string for display or serialization.

Writing Custom Types to a Stream

Many standard types can be written to QDebug objects, and Qt provides support for most Qt value types. To add support for custom types, you need to implement a streaming operator, as in the following example:

QDebug operator<<(QDebug dbg, const Coordinate &c)
{
    dbg.nospace() << "(" << c.x() << ", " << c.y() << ")";

    return dbg.space();
}

This is described in the Debugging Techniques and Creating Custom Qt Types documents.

Member Function Documentation

QDebug::QDebug(QIODevice * device)

Constructs a debug stream that writes to the given device.

QDebug::QDebug(QString * string)

Constructs a debug stream that writes to the given string.

QDebug::QDebug(QtMsgType type)

Constructs a debug stream that writes to the handler for the message type specified by type.

QDebug::QDebug(const QDebug & other)

Constructs a copy of the other debug stream.

QDebug::~QDebug()

Flushes any pending data to be written and destroys the debug stream.

QDebug & QDebug::maybeSpace()

Writes a space character to the debug stream, depending on the last character sent to the stream, and returns a reference to the stream.

If the last character was a space character, this function writes a space character to the stream; otherwise, no characters are written to the stream.

See also space() and nospace().

QDebug & QDebug::nospace()

Clears the stream's internal flag that records whether the last character was a space and returns a reference to the stream.

See also space() and maybeSpace().

QDebug & QDebug::space()

Writes a space character to the debug stream and returns a reference to the stream.

The stream will record that the last character sent to the stream was a space.

See also nospace() and maybeSpace().

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

Writes the character, t, to the stream and returns a reference to the stream.

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

Writes the boolean value, t, to the stream and returns a reference to the stream.

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

Writes the character, t, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(signed short i)

Writes the signed short integer, i, to the stream and returns a reference to the stream.

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

Writes then unsigned short integer, i, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(signed int i)

Writes the signed integer, i, to the stream and returns a reference to the stream.

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

Writes then unsigned integer, i, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(signed long l)

Writes the signed long integer, l, to the stream and returns a reference to the stream.

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

Writes then unsigned long integer, l, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(qint64 i)

Writes the signed 64-bit integer, i, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(quint64 i)

Writes then unsigned 64-bit integer, i, to the stream and returns a reference to the stream.

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

Writes the 32-bit floating point number, f, to the stream and returns a reference to the stream.

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

Writes the 64-bit floating point number, f, to the stream and returns a reference to the stream.

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

Writes the '\0'-terminated string, s, to the stream and returns a reference to the stream.

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

Writes the string, s, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(const QStringRef & s)

Writes the string reference, s, to the stream and returns a reference to the stream.

QDebug & QDebug::operator<<(const QLatin1String & s)

Writes the Latin1-encoded string, s, to the stream and returns a reference to the stream.

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

Writes the byte array, b, to the stream and returns a reference to the stream.

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

Writes a pointer, p, to the stream and returns a reference to the stream.

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

Assigns the other debug stream to this stream and returns a reference to this stream.

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