- Qt 6.11
- Qt Core
- C++ Classes
- QDebug
- Qt 6.11.1 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`
Inherits: | QIODeviceBase
Inherited By: | QQmlInfo

- List of all members, including inherited members
- QDebug is part of Implicitly Shared Classes.

## Public Types

enum | VerbosityLevel { MinimumVerbosity, DefaultVerbosity, MaximumVerbosity }

## Public Functions

`(since 6.9)` | QDebug(QByteArray *byteArray)
| QDebug(QIODevice *device)
| QDebug(QString *string)
| QDebug(QtMsgType t)
| QDebug(const QDebug &o)
| ~QDebug()
bool | autoInsertSpaces() const
QDebug & | maybeQuote(char c = '"')
QDebug & | maybeSpace()
QDebug & | noquote()
QDebug & | nospace()
QDebug & | quote()
`(since 6.7)` bool | quoteStrings() const
QDebug & | resetFormat()
void | setAutoInsertSpaces(bool b)
`(since 6.7)` void | setQuoteStrings(bool b)
void | setVerbosity(int verbosityLevel)
QDebug & | space()
void | swap(QDebug &other)
int | verbosity() const
QDebug & | verbosity(int verbosityLevel)
`(since 6.0)` QDebug & | operator<<(QByteArrayView t)
QDebug & | operator<<(QChar t)
QDebug & | operator<<(QLatin1StringView t)
QDebug & | operator<<(QStringView s)
`(since 6.0)` QDebug & | operator<<(QUtf8StringView s)
`(since 6.7)` QDebug & | operator<<(T i)
`(since 6.7)` QDebug & | operator<<(T i)
QDebug & | operator<<(bool t)
QDebug & | operator<<(char t)
QDebug & | operator<<(char16_t t)
QDebug & | operator<<(char32_t t)
QDebug & | operator<<(const QByteArray &t)
QDebug & | operator<<(const QString &t)
QDebug & | operator<<(const char *t)
`(since 6.0)` QDebug & | operator<<(const char16_t *t)
`(since 6.5)` QDebug & | operator<<(const std::basic_string<Char, Args...> &s)
`(since 6.7)` QDebug & | operator<<(const std::optional<T> &opt)
`(since 6.9)` QDebug & | operator<<(const std::tuple<Ts...> &tuple)
QDebug & | operator<<(const void *t)
QDebug & | operator<<(double t)
QDebug & | operator<<(float t)
QDebug & | operator<<(int t)
QDebug & | operator<<(long t)
QDebug & | operator<<(qint64 t)
QDebug & | operator<<(quint64 t)
QDebug & | operator<<(short t)
`(since 6.5)` QDebug & | operator<<(std::basic_string_view<Char, Args...> s)
`(since 6.6)` QDebug & | operator<<(std::chrono::duration<Rep, Period> duration)
`(since 6.7)` QDebug & | operator<<(std::nullopt_t)
QDebug & | operator<<(unsigned int t)
QDebug & | operator<<(unsigned long t)
QDebug & | operator<<(unsigned short t)
QDebug & | operator=(const QDebug &other)

## Static Public Members

`(since 6.9)` QByteArray | toBytes(const T &object)
`(since 6.0)` QString | toString(const T &object)

## Related Non-Members

QDebug | operator<<(QDebug debug, const QList<T> &list)
QDebug | operator<<(QDebug debug, const QMap<Key, T> &map)
QDebug | operator<<(QDebug debug, const QMultiHash<Key, T> &hash)
QDebug | operator<<(QDebug debug, const QMultiMap<Key, T> &map)
QDebug | operator<<(QDebug debug, const QSet<T> &set)
`(since 6.3)` QDebug | operator<<(QDebug debug, const QVarLengthArray<T, P> &array)
`(since 6.9)` QDebug | operator<<(QDebug debug, const std::array<T, N> &array)
QDebug | operator<<(QDebug debug, const std::list<T, Alloc> &vec)
QDebug | operator<<(QDebug debug, const std::map<Key, T, Compare, Alloc> &map)
QDebug | operator<<(QDebug debug, const std::multimap<Key, T, Compare, Alloc> &map)
`(since 6.9)` QDebug | operator<<(QDebug debug, const std::multiset<Key, Compare, Alloc> &multiset)
QDebug | operator<<(QDebug debug, const std::pair<T1, T2> &pair)
`(since 6.9)` QDebug | operator<<(QDebug debug, const std::set<Key, Compare, Alloc> &set)
`(since 6.9)` QDebug | operator<<(QDebug debug, const std::unordered_map<Key, T, Hash, KeyEqual, Alloc> &map)
`(since 6.9)` QDebug | operator<<(QDebug debug, const std::unordered_set<Key, Hash, KeyEqual, Alloc> &unordered_set)
QDebug | operator<<(QDebug debug, const std::vector<T, Alloc> &vec)
`(since 6.9)` QDebug | operator<<(QDebug debug, T t)
QDebug | operator<<(QDebug debug, const QContiguousCache<T> &cache)
QDebug | operator<<(QDebug debug, const QFlags<T> &flags)
QDebug | operator<<(QDebug debug, const QHash<Key, T> &hash)

## Macros

QDebug | qCritical()
QDebug | qDebug()
QDebug | qFatal()
QDebug | qInfo()
QDebug | qWarning()

## 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 qInfo(), 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

### enum QDebug::VerbosityLevel

This enum describes the range of verbosity levels.

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

See also verbosity() and setVerbosity().

## Member Function Documentation

### `[explicit, since 6.9]` QDebug::QDebug(QByteArray *byteArray)

Constructs a debug stream that writes to the given byteArray.

The data is encoded in UTF-8, which may not be the same as the system locale, for example, on Windows.

With objects instantiated with this constructor, the data may be buffered and won't be written to the byte array until the stream is flushed, for example, by using Qt::flush.

This function was introduced in Qt 6.9.

See also QTextStream manipulators.

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

Constructs a debug stream that writes to the given device.

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

Constructs a debug stream that writes to the given string.

### `[explicit]` QDebug::QDebug(QtMsgType t)

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

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

Constructs a copy of the other debug stream o.

### `[noexcept]` QDebug::~QDebug()

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

### bool QDebug::autoInsertSpaces() const

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

See also setAutoInsertSpaces() and QDebugStateSaver.

### 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 `"`.

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().

### 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.

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().

### 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.

See also noquote() and maybeQuote().

### `[noexcept, since 6.7]` bool QDebug::quoteStrings() const

Returns `true` if this QDebug instance will quote strings streamed into it (which is the default).

This function was introduced in Qt 6.7.

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

### QDebug &QDebug::resetFormat()

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

See also space() and quote().

### void QDebug::setAutoInsertSpaces(bool b)

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

See also autoInsertSpaces() and QDebugStateSaver.

### `[since 6.7]` void QDebug::setQuoteStrings(bool b)

Enables quoting of strings streamed into this QDebug instance if b is `true`; otherwise quoting is disabled.

The default is to quote strings.

This function was introduced in Qt 6.7.

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

### 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.

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().

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

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

### `[static, since 6.9]` template <typename T> QByteArray QDebug::toBytes(const T &object)

This is equivalent to passing object to `QDebug::toString(object).toUtf8()`, but more efficient.

This function was introduced in Qt 6.9.

See also toString().

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

     QString str = QDebug::toString(list);

The string is streamed using nospace().

This function was introduced in Qt 6.0.

See also toBytes().

### 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.

See also setVerbosity() and VerbosityLevel.

### 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.

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

### `[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<<(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<<(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<<(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.

### `[since 6.0]` QDebug &QDebug::operator<<(QUtf8StringView 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.

### `[since 6.7]` template <typename T, QDebug::if_qint128<T> = true> QDebug &QDebug::operator<<(T i)

### `[since 6.7]` template <typename T, QDebug::if_quint128<T> = true> QDebug &QDebug::operator<<(T i)

Prints the textual representation of the 128-bit integer i.

Note: This operator is only available if Qt supports 128-bit integer types. If 128-bit integer types are available in your build, but the Qt libraries were compiled without, the operator will print a warning instead.

Note: Because the operator is a function template, no implicit conversions are performed on its argument. It must be exactly qint128/quint128.

These functions were introduced in Qt 6.7.

See also QT_SUPPORTS_INT128.

### 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<<(char16_t t)

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

### QDebug &QDebug::operator<<(char32_t t)

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

### 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.

### 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"

### 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.

### `[since 6.5]` template <typename Char, typename... Args> QDebug &QDebug::operator<<(const std::basic_string<Char, Args...> &s)

### `[since 6.5]` template <typename Char, typename... Args> QDebug &QDebug::operator<<(std::basic_string_view<Char, Args...> s)

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

These operators only participate in overload resolution if `Char` is one of

- char
- char8_t (C++20 only)
- char16_t
- char32_t
- wchar_t

These functions were introduced in Qt 6.5.

### `[since 6.7]` template <typename T, QDebug::if_streamable<T> = true> QDebug &QDebug::operator<<(const std::optional<T> &opt)

Writes the contents of opt (or `nullopt` if not set) to this stream. `T` needs to support streaming into QDebug.

This function was introduced in Qt 6.7.

### `[since 6.9]` template <typename... Ts, QDebug::if_streamable<Ts...> = true> QDebug &QDebug::operator<<(const std::tuple<Ts...> &tuple)

Writes the contents of tuple to the stream. All `Ts...` need to support streaming into QDebug.

This function was introduced in Qt 6.9.

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

Writes a pointer, 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<<(float t)

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

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

Writes the signed 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<<(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<<(short t)

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

### `[since 6.6]` template <typename Rep, typename Period> QDebug &QDebug::operator<<(std::chrono::duration<Rep, Period> duration)

Prints the time duration duration to the stream and returns a reference to the stream. The printed string is the numeric representation of the period followed by the time unit, similar to what the C++ Standard Library would produce with `std::ostream`.

The unit is not localized.

This function was introduced in Qt 6.6.

### `[since 6.7]` QDebug &QDebug::operator<<(std::nullopt_t)

Writes nullopt to the stream.

This function was introduced in Qt 6.7.

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

Writes then unsigned 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<<(unsigned short t)

Writes then unsigned short integer, t, 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.

## 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.

### 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 QMultiHash<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 QMultiMap<Key, T> &map)

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

### 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.

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

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

This function was introduced in Qt 6.3.

### `[since 6.9]` template <typename T, std::size_t N> QDebug operator<<(QDebug debug, const std::array<T, N> &array)

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

This function was introduced in Qt 6.9.

### template <typename T, typename Alloc> QDebug operator<<(QDebug debug, const std::list<T, Alloc> &vec)

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

### template < typename Key, typename T, typename Compare, typename Alloc > QDebug operator<<(QDebug debug, const std::map<Key, T, Compare, Alloc> &map)

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

### template < typename Key, typename T, typename Compare, typename Alloc > QDebug operator<<(QDebug debug, const std::multimap<Key, T, Compare, Alloc> &map)

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

### `[since 6.9]` template < typename Key, typename Compare, typename Alloc > QDebug operator<<(QDebug debug, const std::multiset<Key, Compare, Alloc> &multiset)

Writes the contents of multiset to debug. The `Key` type needs to support streaming into QDebug.

This function was introduced in Qt 6.9.

### template <typename T1, typename T2> QDebug operator<<(QDebug debug, const std::pair<T1, T2> &pair)

Writes the contents of pair to debug. Both `T1` and `T2` need to support streaming into QDebug.

### `[since 6.9]` template < typename Key, typename Compare, typename Alloc > QDebug operator<<(QDebug debug, const std::set<Key, Compare, Alloc> &set)

Writes the contents of set to debug. The `Key` type needs to support streaming into QDebug.

This function was introduced in Qt 6.9.

### `[since 6.9]` template < typename Key, typename T, typename Hash, typename KeyEqual, typename Alloc > QDebug operator<<(QDebug debug, const std::unordered_map<Key, T, Hash, KeyEqual, Alloc> &map)

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

This function was introduced in Qt 6.9.

### `[since 6.9]` template < typename Key, typename Hash, typename KeyEqual, typename Alloc > QDebug operator<<(QDebug debug, const std::unordered_set<Key, Hash, KeyEqual, Alloc> &unordered_set)

Writes the contents of unordered_set to debug. The `Key` type needs to support streaming into QDebug.

This function was introduced in Qt 6.9.

### template <typename T, typename Alloc> QDebug operator<<(QDebug debug, const std::vector<T, Alloc> &vec)

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

### `[since 6.9]` template <typename T, QDebug::if_ordering_type<T> = true> QDebug operator<<(QDebug debug, T t)

Prints the Qt or std ordering value t to the debug object.

#### Constraints

Participates in overload resolution only if `T` is one of <Qt/Std>::<weak/partial/strong>_ordering.

This function was introduced in Qt 6.9.

### 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.

### 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.

## Macro Documentation

### QDebug qCritical()

Returns a QDebug object that logs a critical message to the central message handler.

Example:

     qCritical() << "Brush:" << myQBrush << "Other value:" << i;

Using qCritical() is an alternative to qCritical(const char *, ...), which follows the printf paradigm.

Note that QDebug and the type specific stream operators do add various formatting to make the debug message easier to read. See the formatting options documentation for more details.

For debugging purposes, it is sometimes convenient to let the program abort for critical messages. This allows you then to inspect the core dump, or attach a debugger - see also qFatal(). To enable this, set the environment variable `QT_FATAL_CRITICALS` to a number `n`. The program terminates then for the n-th critical message. That is, if the environment variable is set to 1, it will terminate on the first call; if it contains the value 10, it will exit on the 10th call. Any non-numeric value in the environment variable is equivalent to 1.

Note: This macro is thread-safe.

See also qCritical(const char *, ...) and qCCritical().

### QDebug qDebug()

Returns a QDebug object that logs a debug message to the central message handler.

Example:

     qDebug() << "Brush:" << myQBrush << "Other value:" << i;

Using qDebug() is an alternative to qDebug(const char *, ...), which follows the printf paradigm.

Note that QDebug and the type specific stream operators do add various formatting to make the debug message easier to read. See the formatting options documentation for more details.

This function does nothing if `QT_NO_DEBUG_OUTPUT` was defined during compilation.

Note: This macro is thread-safe.

See also qDebug(const char *, ...) and qCDebug().

### QDebug qFatal()

Returns a QDebug object that logs a fatal message to the central message handler.

Using qFatal() is an alternative to qFatal(const char *, ...), which follows the printf paradigm.

Note that QDebug and the type specific stream operators do add various formatting to make the debug message easier to read. See the formatting options documentation for more details.

If you are using the default message handler, the returned stream will abort to create a core dump. On Windows, for debug builds, this function will report a _CRT_ERROR enabling you to connect a debugger to the application.

Note: This macro is thread-safe.

See also qFatal(const char *, ...) and qCFatal().

### QDebug qInfo()

Returns a QDebug object that logs an informational message to the central message handler.

Example:

     qInfo() << "Brush:" << myQBrush << "Other value:" << i;

Using qInfo() is an alternative to qInfo(const char *, ...), which follows the printf paradigm.

Note that QDebug and the type specific stream operators do add various formatting to make the debug message easier to read. See the formatting options documentation for more details.

This function does nothing if `QT_NO_INFO_OUTPUT` was defined during compilation.

Note: This macro is thread-safe.

See also qInfo(const char *, ...) and qCInfo().

### QDebug qWarning()

Returns a QDebug object that logs a warning message to the central message handler.

Example:

     qWarning() << "Brush:" << myQBrush << "Other value:" << i;

Using qWarning() is an alternative to qWarning(const char *, ...), which follows the printf paradigm.

Note that QDebug and the type specific stream operators do add various formatting to make the debug message easier to read. See the formatting options documentation for more details.

This function does nothing if `QT_NO_WARNING_OUTPUT` was defined during compilation.

For debugging purposes, it is sometimes convenient to let the program abort for warning messages. This allows you then to inspect the core dump, or attach a debugger - see also qFatal(). To enable this, set the environment variable `QT_FATAL_WARNINGS` to a number `n`. The program terminates then for the n-th warning. That is, if the environment variable is set to 1, it will terminate on the first call; if it contains the value 10, it will exit on the 10th call. Any non-numeric value in the environment variable is equivalent to 1.

Note: This macro is thread-safe.

See also qWarning(const char *, ...) and qCWarning().