QDebug Class | Qt Core 6.4.1

- Qt 6.4
- Qt Core
- C++ Classes
- QDebug
- Qt 6.4.1 Reference Documentation

# QDebug Class

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

Header: | #include <QDebug>
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

enum | VerbosityLevel { MinimumVerbosity, DefaultVerbosity, MaximumVerbosity }

## Public Functions

| QDebug(const QDebug &o)
| QDebug(QtMsgType t)
| QDebug(QString *string)
| QDebug(QIODevice *device)
QDebug & | operator=(const QDebug &other)
| ~QDebug()
bool | autoInsertSpaces() const
QDebug & | maybeQuote(char c = '"')
QDebug & | maybeSpace()
QDebug & | noquote()
QDebug & | nospace()
QDebug & | quote()
QDebug & | resetFormat()
void | setAutoInsertSpaces(bool b)
void | setVerbosity(int verbosityLevel)
QDebug & | space()
void | swap(QDebug &other)
QDebug & | verbosity(int verbosityLevel)
int | verbosity() const
QDebug & | operator<<(QChar t)
QDebug & | operator<<(bool t)
QDebug & | operator<<(char t)
QDebug & | operator<<(short t)
QDebug & | operator<<(unsigned short t)
QDebug & | operator<<(char16_t t)
QDebug & | operator<<(char32_t t)
QDebug & | operator<<(int s)
QDebug & | operator<<(unsigned int t)
QDebug & | operator<<(long t)
QDebug & | operator<<(unsigned long t)
QDebug & | operator<<(qint64 t)
QDebug & | operator<<(quint64 t)
QDebug & | operator<<(float t)
QDebug & | operator<<(double t)
QDebug & | operator<<(const char *t)
QDebug & | operator<<(const char16_t *t)
QDebug & | operator<<(const QString &t)
QDebug & | operator<<(QStringView s)
QDebug & | operator<<(QLatin1StringView t)
QDebug & | operator<<(const QByteArray &t)
QDebug & | operator<<(QByteArrayView t)
QDebug & | operator<<(const void *t)

## Static Public Members

QString | toString(T &&object)

## Related Non-Members

QDebug | operator<<(QDebug debug, const QList<T> &list)
QDebug | operator<<(QDebug debug, const QVarLengthArray<T, P> &array = P)
QDebug | operator<<(QDebug debug, const int &vec)
QDebug | operator<<(QDebug debug, const QSet<T> &set)
QDebug | operator<<(QDebug debug, const QMap<Key, T> &map)
QDebug | operator<<(QDebug debug, const QMultiMap<Key, T> &map)
QDebug | operator<<(QDebug debug, const QHash<Key, T> &hash)
QDebug | operator<<(QDebug debug, const QMultiHash<Key, T> &hash)
QDebug | operator<<(QDebug debug, const QContiguousCache<T> &cache)
QDebug | operator<<(QDebug debug, const QFlags<T> &flags)

## Detailed Description

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.

### Formatting Options

QDebug formats output so that it's easily readable. It automatically adds spaces between arguments, and adds quotes around QString, QByteArray, QChar arguments.

You can tweak these options through the space(), nospace() and quote(), noquote() methods. Furthermore, QTextStream manipulators can be piped into a QDebug stream.

QDebugStateSaver limits changes to the formatting to the current scope. resetFormat() resets the options to the default ones.

### 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 debug, const Coordinate &c)
     {
         QDebugStateSaver saver(debug);
         debug.nospace() << '(' << c.x() << ", " << c.y() << ')';

         return debug;
     }

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

## Member Type Documentation

### `[since 5.13]` enum QDebug::VerbosityLevel

This enum describes the range of verbosity levels.

Constant | Value
--- | ---
`QDebug::MinimumVerbosity` | `0`
`QDebug::DefaultVerbosity` | `2`
`QDebug::MaximumVerbosity` | `7`

This enum was introduced or modified in Qt 5.13.

See also verbosity() and setVerbosity().

## Member Function Documentation

### QDebug::QDebug(const QDebug &o)

Constructs a copy of the other debug stream o.

### QDebug::QDebug(QtMsgType t)

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

### QDebug::QDebug(QString *string)

Constructs a debug stream that writes to the given string.

### QDebug::QDebug(QIODevice *device)

Constructs a debug stream that writes to the given device.

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

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

### QDebug::~QDebug()

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

### `[since 5.0]` bool QDebug::autoInsertSpaces() const

Returns `true` if this QDebug instance will automatically insert spaces between writes.

This function was introduced in Qt 5.0.

See also setAutoInsertSpaces() and QDebugStateSaver.

### `[since 5.4]` QDebug &QDebug::maybeQuote(char c = '"')

Writes a character c to the debug stream, depending on the current setting for automatic insertion of quotes, and returns a reference to the stream.

The default character is a double quote `"`.

This function was introduced in Qt 5.4.

See also quote() and noquote().

### QDebug &QDebug::maybeSpace()

Writes a space character to the debug stream, depending on the current setting for automatic insertion of spaces, and returns a reference to the stream.

See also space() and nospace().

### `[since 5.4]` QDebug &QDebug::noquote()

Disables automatic insertion of quotation characters around QChar, QString and QByteArray contents and returns a reference to the stream.

When quoting is disabled, these types are printed without quotation characters and without escaping of non-printable characters.

This function was introduced in Qt 5.4.

See also quote() and maybeQuote().

### QDebug &QDebug::nospace()

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

See also space() and maybeSpace().

### `[since 5.4]` QDebug &QDebug::quote()

Enables automatic insertion of quotation characters around QChar, QString and QByteArray contents and returns a reference to the stream.

Quoting is enabled by default.

This function was introduced in Qt 5.4.

See also noquote() and maybeQuote().

### `[since 5.4]` QDebug &QDebug::resetFormat()

Resets the stream formatting options, bringing it back to its original constructed state.

This function was introduced in Qt 5.4.

See also space() and quote().

### `[since 5.0]` void QDebug::setAutoInsertSpaces(bool b)

Enables automatic insertion of spaces between writes if b is true; otherwise automatic insertion of spaces is disabled.

This function was introduced in Qt 5.0.

See also autoInsertSpaces() and QDebugStateSaver.

### `[since 5.6]` void QDebug::setVerbosity(int verbosityLevel)

Sets the verbosity of the stream to verbosityLevel.

The allowed range is from 0 to 7. The default value is 2.

This function was introduced in Qt 5.6.

See also verbosity() and VerbosityLevel.

### QDebug &QDebug::space()

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

The stream remembers that automatic insertion of spaces is enabled for future writes.

See also nospace() and maybeSpace().

### `[since 5.0]` void QDebug::swap(QDebug &other)

Swaps this debug stream instance with other. This function is very fast and never fails.

This function was introduced in Qt 5.0.

### `[static, since 6.0]` template <typename T> QString QDebug::toString(T &&object)

Streams object into a QDebug instance that operates on a string, and then returns that string.

This function is useful for cases where you need the textual representation of an object for debugging, but cannot use `operator<<`. For example:

         QTRY_VERIFY2(list.isEmpty(), qPrintable(QString::fromLatin1(
             "Expected list to be empty, but it has the following items: %1")).arg(QDebug::toString(list)));

The string is streamed using nospace().

This function was introduced in Qt 6.0.

### `[since 5.13]` QDebug &QDebug::verbosity(int verbosityLevel)

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

The allowed range is from 0 to 7. The default value is 2.

This function was introduced in Qt 5.13.

See also verbosity(), setVerbosity(), and VerbosityLevel.

### `[since 5.6]` int QDebug::verbosity() const

Returns the verbosity of the debug stream.

Streaming operators can check the value to decide whether verbose output is desired and print more information depending on the level. Higher values indicate that more information is desired.

The allowed range is from 0 to 7. The default value is 2.

This function was introduced in Qt 5.6.

See also setVerbosity() and VerbosityLevel.

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

Writes the character, t, to the stream and returns a reference to the stream. Normally, QDebug prints control characters and non-US-ASCII characters as their C escape sequences or their Unicode value (\u1234). To print non-printable characters without transformation, enable the noquote() functionality, but note that some QDebug backends may not be 8-bit clean and may not be able to represent `t`.

### 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<<(short t)

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

### QDebug &QDebug::operator<<(unsigned short t)

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

### `[since 5.5]` QDebug &QDebug::operator<<(char16_t t)

Writes the UTF-16 character, t, to the stream and returns a reference to the stream.

This function was introduced in Qt 5.5.

### `[since 5.5]` QDebug &QDebug::operator<<(char32_t t)

Writes the UTF-32 character, t, to the stream and returns a reference to the stream.

This function was introduced in Qt 5.5.

### `[since 6.0]` QDebug &QDebug::operator<<(int s)

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

Normally, QDebug prints the data inside quotes and transforms control or non-US-ASCII characters to their C escape sequences (\xAB). This way, the output is always 7-bit clean and the string can be copied from the output and pasted back into C++ sources, if necessary.

To print non-printable characters without transformation, enable the noquote() functionality. Note that some QDebug backends might not be 8-bit clean.

This function was introduced in Qt 6.0.

### QDebug &QDebug::operator<<(unsigned int t)

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

### QDebug &QDebug::operator<<(long t)

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

### QDebug &QDebug::operator<<(unsigned long t)

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

### QDebug &QDebug::operator<<(qint64 t)

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

### QDebug &QDebug::operator<<(quint64 t)

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

### QDebug &QDebug::operator<<(float t)

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

### QDebug &QDebug::operator<<(double t)

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

### QDebug &QDebug::operator<<(const char *t)

Writes the '\0'-terminated UTF-8 string, t, to the stream and returns a reference to the stream. The string is never quoted or escaped for the output. Note that QDebug buffers internally as UTF-16 and may need to transform to 8-bit using the locale's codec in order to use some backends, which may cause garbled output (mojibake). Restricting to US-ASCII strings is recommended.

### `[since 6.0]` QDebug &QDebug::operator<<(const char16_t *t)

Writes the u'\0'-terminated UTF-16 string, t, to the stream and returns a reference to the stream. The string is never quoted or escaped for the output. Note that QDebug buffers internally as UTF-16 and may need to transform to 8-bit using the locale's codec in order to use some backends, which may cause garbled output (mojibake). Restricting to US-ASCII strings is recommended.

This function was introduced in Qt 6.0.

### QDebug &QDebug::operator<<(const QString &t)

Writes the string, t, to the stream and returns a reference to the stream. Normally, QDebug prints the string inside quotes and transforms non-printable characters to their Unicode values (\u1234).

To print non-printable characters without transformation, enable the noquote() functionality. Note that some QDebug backends might not be 8-bit clean.

Output examples:

         QString s;

         s = "a";
         qDebug().noquote() << s;    // prints: a
         qDebug() << s;              // prints: "a"

         s = "\"a\r\n\"";
         qDebug() << s;              // prints: "\"a\r\n\""

         s = "\033";                 // escape character
         qDebug() << s;              // prints: "\u001B"

         s = "\u00AD";               // SOFT HYPHEN
         qDebug() << s;              // prints: "\u00AD"

         s = "\u00E1";               // LATIN SMALL LETTER A WITH ACUTE
         qDebug() << s;              // prints: "á"

         s = "a\u0301";              // "a" followed by COMBINING ACUTE ACCENT
         qDebug() << s;              // prints: "á";

         s = "\u0430\u0301";         // CYRILLIC SMALL LETTER A followed by COMBINING ACUTE ACCENT
         qDebug() << s;              // prints: "а́"

### `[since 5.10]` QDebug &QDebug::operator<<(QStringView s)

Writes the string view, s, to the stream and returns a reference to the stream. Normally, QDebug prints the string inside quotes and transforms non-printable characters to their Unicode values (\u1234).

To print non-printable characters without transformation, enable the noquote() functionality. Note that some QDebug backends might not be 8-bit clean.

See the QString overload for examples.

This function was introduced in Qt 5.10.

### QDebug &QDebug::operator<<(QLatin1StringView t)

Writes the string, t, to the stream and returns a reference to the stream. Normally, QDebug prints the string inside quotes and transforms non-printable characters to their Unicode values (\u1234).

To print non-printable characters without transformation, enable the noquote() functionality. Note that some QDebug backends might not be 8-bit clean.

See the QString overload for examples.

### QDebug &QDebug::operator<<(const QByteArray &t)

Writes the byte array, t, to the stream and returns a reference to the stream. Normally, QDebug prints the array inside quotes and transforms control or non-US-ASCII characters to their C escape sequences (\xAB). This way, the output is always 7-bit clean and the string can be copied from the output and pasted back into C++ sources, if necessary.

To print non-printable characters without transformation, enable the noquote() functionality. Note that some QDebug backends might not be 8-bit clean.

Output examples:

         QByteArray ba;

         ba = "a";
         qDebug().noquote() << ba;    // prints: a
         qDebug() << ba;              // prints: "a"

         ba = "\"a\r\n\"";
         qDebug() << ba;              // prints: "\"a\r\n\""

         ba = "\033";                 // escape character
         qDebug() << ba;              // prints: "\x1B"

         ba = "\xC3\xA1";
         qDebug() << ba;              // prints: "\xC3\xA1"

         ba = QByteArray("a\0b", 3);
         qDebug() << ba               // prints: "\a\x00""b"

Note how QDebug needed to close and reopen the string in the way C and C++ languages concatenate string literals so that the letter 'b' is not interpreted as part of the previous hexadecimal escape sequence.

### `[since 6.0]` QDebug &QDebug::operator<<(QByteArrayView t)

Writes the data of the observed byte array, t, to the stream and returns a reference to the stream.

Normally, QDebug prints the data inside quotes and transforms control or non-US-ASCII characters to their C escape sequences (\xAB). This way, the output is always 7-bit clean and the string can be copied from the output and pasted back into C++ sources, if necessary.

To print non-printable characters without transformation, enable the noquote() functionality. Note that some QDebug backends might not be 8-bit clean.

See the QByteArray overload for examples.

This function was introduced in Qt 6.0.

### QDebug &QDebug::operator<<(const void *t)

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

## Related Non-Members

### template <typename T> QDebug operator<<(QDebug debug, const QList<T> &list)

Writes the contents of list to debug. `T` needs to support streaming into QDebug.

### `[since 6.3]` template <typename T, int P> QDebug operator<<(QDebug debug, const QVarLengthArray<T, P> &array = P)

Writes the contents of array to debug. `T` needs to support streaming into QDebug.

This function was introduced in Qt 6.3.

### `[since 5.7]` template <typename T, typename Alloc> QDebug operator<<(QDebug debug, const int &vec)

Writes the contents of list vec to debug. `T` needs to support streaming into QDebug.

This function was introduced in Qt 5.7.

### template <typename T> QDebug operator<<(QDebug debug, const QSet<T> &set)

Writes the contents of set to debug. `T` needs to support streaming into QDebug.

### template <typename Key, typename T> QDebug operator<<(QDebug debug, const QMap<Key, T> &map)

Writes the contents of map to debug. Both `Key` and `T` need to support streaming into QDebug.

### template <typename Key, typename T> QDebug operator<<(QDebug debug, const QMultiMap<Key, T> &map)

Writes the contents of map to debug. Both `Key` and `T` need to support streaming into QDebug.

### template <typename Key, typename T> QDebug operator<<(QDebug debug, const QHash<Key, T> &hash)

Writes the contents of hash to debug. Both `Key` and `T` need to support streaming into QDebug.

### template <typename Key, typename T> QDebug operator<<(QDebug debug, const QMultiHash<Key, T> &hash)

Writes the contents of hash to debug. Both `Key` and `T` need to support streaming into QDebug.

### template <typename T> QDebug operator<<(QDebug debug, const QContiguousCache<T> &cache)

Writes the contents of cache to debug. `T` needs to support streaming into QDebug.

### template <typename T> QDebug operator<<(QDebug debug, const QFlags<T> &flags)

Writes flags to debug.