Qt Reference Documentation

# QFlags Class Reference

The QFlags class provides a type-safe way of storing OR-combinations of enum values. More...

     #include <QFlags>

- List of all members, including inherited members

## Public Types

typedef | enum_type

## Public Functions

| QFlags ( const QFlags & other )
| QFlags ( Enum flag )
| QFlags ( Zero zero = 0 )
| QFlags ( QFlag value )
bool | testFlag ( Enum flag ) const
| operator int () const
bool | operator! () const
QFlags | operator& ( int mask ) const
QFlags | operator& ( uint mask ) const
QFlags | operator& ( Enum mask ) const
QFlags & | operator&= ( int mask )
QFlags & | operator&= ( uint mask )
QFlags & | operator= ( const QFlags & other )
QFlags | operator^ ( QFlags other ) const
QFlags | operator^ ( Enum other ) const
QFlags & | operator^= ( QFlags other )
QFlags & | operator^= ( Enum other )
QFlags | operator| ( QFlags other ) const
QFlags | operator| ( Enum other ) const
QFlags & | operator|= ( QFlags other )
QFlags & | operator|= ( Enum other )
QFlags | operator~ () const

## Macros

| Q_DECLARE_FLAGS ( Flags, Enum )
| Q_DECLARE_OPERATORS_FOR_FLAGS ( Flags )

## Detailed Description

The QFlags class provides a type-safe way of storing OR-combinations of enum values.

The QFlags<Enum> class is a template class, where Enum is an enum type. QFlags is used throughout Qt for storing combinations of enum values.

The traditional C++ approach for storing OR-combinations of enum values is to use an `int` or `uint` variable. The inconvenience with this approach is that there's no type checking at all; any enum value can be OR'd with any other enum value and passed on to a function that takes an `int` or `uint`.

Qt uses QFlags to provide type safety. For example, the Qt::Alignment type is simply a typedef for QFlags<Qt::AlignmentFlag>. QLabel::setAlignment() takes a Qt::Alignment parameter, which means that any combination of Qt::AlignmentFlag values,or 0, is legal:

     label->setAlignment(Qt::AlignLeft | Qt::AlignTop);

If you try to pass a value from another enum or just a plain integer other than 0, the compiler will report an error. If you need to cast integer values to flags in a untyped fashion, you can use the explicit QFlags constructor as cast operator.

If you want to use QFlags for your own enum types, use the Q_DECLARE_FLAGS() and Q_DECLARE_OPERATORS_FOR_FLAGS().

Example:

     class MyClass
     {
     public:
         enum Option {
             NoOptions = 0x0,
             ShowTabs = 0x1,
             ShowAll = 0x2,
             SqueezeBlank = 0x4
         };
         Q_DECLARE_FLAGS(Options, Option)
         ...
     };

     Q_DECLARE_OPERATORS_FOR_FLAGS(MyClass::Options)

You can then use the `MyClass::Options` type to store combinations of `MyClass::Option` values.

### Flags and the Meta-Object System

The Q_DECLARE_FLAGS() macro does not expose the flags to the meta-object system, so they cannot be used by Qt Script or edited in Qt Designer. To make the flags available for these purposes, the Q_FLAGS() macro must be used:

     Q_FLAGS(Options)

### Naming Convention

A sensible naming convention for enum types and associated QFlags types is to give a singular name to the enum type (e.g., `Option`) and a plural name to the QFlags type (e.g., `Options`). When a singular name is desired for the QFlags type (e.g., `Alignment`), you can use `Flag` as the suffix for the enum type (e.g., `AlignmentFlag`).

See also QFlag.

## Member Type Documentation

### typedef QFlags::enum_type

Typedef for the Enum template type.

## Member Function Documentation

### QFlags::QFlags ( const QFlags & other )

Constructs a copy of other.

### QFlags::QFlags ( Enum flag )

Constructs a QFlags object storing the given flag.

### QFlags::QFlags ( Zero zero = 0 )

Constructs a QFlags object with no flags set. zero must be a literal 0 value.

### QFlags::QFlags ( QFlag value )

Constructs a QFlags object initialized with the given integer value.

The QFlag type is a helper type. By using it here instead of `int`, we effectively ensure that arbitrary enum values cannot be cast to a QFlags, whereas untyped enum values (i.e., `int` values) can.

### bool QFlags::testFlag ( Enum flag ) const

Returns true if the flag is set, otherwise false.

This function was introduced in Qt 4.2.

### QFlags::operator int () const

Returns the value stored in the QFlags object as an integer.

### bool QFlags::operator! () const

Returns true if no flag is set (i.e., if the value stored by the QFlags object is 0); otherwise returns false.

### QFlags QFlags::operator& ( int mask ) const

Returns a QFlags object containing the result of the bitwise AND operation on this object and mask.

See also operator&=(), operator|(), operator^(), and operator~().

### QFlags QFlags::operator& ( uint mask ) const

This is an overloaded function.

### QFlags QFlags::operator& ( Enum mask ) const

This is an overloaded function.

### QFlags & QFlags::operator&= ( int mask )

Performs a bitwise AND operation with mask and stores the result in this QFlags object. Returns a reference to this object.

See also operator&(), operator|=(), and operator^=().

### QFlags & QFlags::operator&= ( uint mask )

This is an overloaded function.

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

Assigns other to this object and returns a reference to this object.

### QFlags QFlags::operator^ ( QFlags other ) const

Returns a QFlags object containing the result of the bitwise XOR operation on this object and other.

See also operator^=(), operator&(), operator|(), and operator~().

### QFlags QFlags::operator^ ( Enum other ) const

This is an overloaded function.

### QFlags & QFlags::operator^= ( QFlags other )

Performs a bitwise XOR operation with other and stores the result in this QFlags object. Returns a reference to this object.

See also operator^(), operator&=(), and operator|=().

### QFlags & QFlags::operator^= ( Enum other )

This is an overloaded function.

### QFlags QFlags::operator| ( QFlags other ) const

Returns a QFlags object containing the result of the bitwise OR operation on this object and other.

See also operator|=(), operator^(), operator&(), and operator~().

### QFlags QFlags::operator| ( Enum other ) const

This is an overloaded function.

### QFlags & QFlags::operator|= ( QFlags other )

Performs a bitwise OR operation with other and stores the result in this QFlags object. Returns a reference to this object.

See also operator|(), operator&=(), and operator^=().

### QFlags & QFlags::operator|= ( Enum other )

This is an overloaded function.

### QFlags QFlags::operator~ () const

Returns a QFlags object that contains the bitwise negation of this object.

See also operator&(), operator|(), and operator^().

## Macro Documentation

### Q_DECLARE_FLAGS ( Flags, Enum )

The Q_DECLARE_FLAGS() macro expands to

     typedef QFlags<Enum> Flags;

Enum is the name of an existing enum type, whereas Flags is the name of the QFlags<Enum> typedef.

See the QFlags documentation for details.

See also Q_DECLARE_OPERATORS_FOR_FLAGS().

### Q_DECLARE_OPERATORS_FOR_FLAGS ( Flags )

The Q_DECLARE_OPERATORS_FOR_FLAGS() macro declares global `operator|()` functions for Flags, which is of type QFlags<T>.

See the QFlags documentation for details.

See also Q_DECLARE_FLAGS().