- Qt 6.9
- Qt Core
- C++ Classes
- QMetaContainer
- Qt 6.9.3 Reference Documentation

# QMetaContainer Class

The QMetaContainer class provides common functionality for sequential and associative containers. More...

Header: | `#include <QMetaContainer>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`
Since: | Qt 6.0
Inherited By: | QMetaSequence

- List of all members, including inherited members

This class is equality-comparable.

## Public Functions

void | advanceConstIterator(void *iterator, qsizetype step) const
void | advanceIterator(void *iterator, qsizetype step) const
void * | begin(void *container) const
bool | canClear() const
void | clear(void *container) const
bool | compareConstIterator(const void *i, const void *j) const
bool | compareIterator(const void *i, const void *j) const
void * | constBegin(const void *container) const
void * | constEnd(const void *container) const
void | copyConstIterator(void *target, const void *source) const
void | copyIterator(void *target, const void *source) const
void | destroyConstIterator(const void *iterator) const
void | destroyIterator(const void *iterator) const
qsizetype | diffConstIterator(const void *i, const void *j) const
qsizetype | diffIterator(const void *i, const void *j) const
void * | end(void *container) const
bool | hasBidirectionalIterator() const
bool | hasConstIterator() const
bool | hasForwardIterator() const
bool | hasInputIterator() const
bool | hasIterator() const
bool | hasRandomAccessIterator() const
bool | hasSize() const
qsizetype | size(const void *container) const

## Detailed Description

QMetaContainer is part of Qt's meta-type system that allows type-erased access to container-like types at runtime.

It serves as a common base for accessing properties of containers in a generic way, such as size, iteration, and clearing operations, without knowing the actual container type.

Derived classes, such as QMetaSequence, provide specialized interfaces for sequential containers.

## Member Function Documentation

### void QMetaContainer::advanceConstIterator(void *iterator, qsizetype step) const

Advances the const iterator by step steps. If step is negative the iterator is moved backwards, towards the beginning of the container. The behavior is unspecified for negative values of step if hasBidirectionalIterator() returns false.

See also constBegin() and constEnd().

### void QMetaContainer::advanceIterator(void *iterator, qsizetype step) const

Advances the non-const iterator by step steps. If step is negative the iterator is moved backwards, towards the beginning of the container. The behavior is unspecified for negative values of step if hasBidirectionalIterator() returns false.

See also begin() and end().

### void *QMetaContainer::begin(void *container) const

Creates and returns a non-const iterator pointing to the beginning of container. The iterator is allocated on the heap using new. It has to be destroyed using destroyIterator eventually, to reclaim the memory.

Returns `nullptr` if the container doesn't offer any non-const iterators.

See also end(), constBegin(), constEnd(), and destroyIterator().

### bool QMetaContainer::canClear() const

Returns `true` if the container can be cleared, `false` otherwise.

See also clear().

### void QMetaContainer::clear(void *container) const

Clears the given container if it can be cleared.

See also canClear().

### bool QMetaContainer::compareConstIterator(const void *i, const void *j) const

Returns `true` if the const iterators i and j point to the same value in the container they are iterating over, otherwise returns `false`.

See also constBegin() and constEnd().

### bool QMetaContainer::compareIterator(const void *i, const void *j) const

Returns `true` if the non-const iterators i and j point to the same value in the container they are iterating over, otherwise returns `false`.

See also begin() and end().

### void *QMetaContainer::constBegin(const void *container) const

Creates and returns a const iterator pointing to the beginning of container. The iterator is allocated on the heap using new. It has to be destroyed using destroyConstIterator eventually, to reclaim the memory.

Returns `nullptr` if the container doesn't offer any const iterators.

See also constEnd(), begin(), end(), and destroyConstIterator().

### void *QMetaContainer::constEnd(const void *container) const

Creates and returns a const iterator pointing to the end of container. The iterator is allocated on the heap using new. It has to be destroyed using destroyConstIterator eventually, to reclaim the memory.

Returns `nullptr` if the container doesn't offer any const iterators.

See also constBegin(), begin(), end(), and destroyConstIterator().

### void QMetaContainer::copyConstIterator(void *target, const void *source) const

Copies the const iterator source into the const iterator target. Afterwards compareConstIterator(target, source) returns `true`.

See also constBegin() and constEnd().

### void QMetaContainer::copyIterator(void *target, const void *source) const

Copies the non-const iterator source into the non-const iterator target. Afterwards compareIterator(target, source) returns `true`.

See also begin() and end().

### void QMetaContainer::destroyConstIterator(const void *iterator) const

Destroys a const iterator previously created using constBegin() or constEnd().

See also constBegin(), constEnd(), and destroyIterator().

### void QMetaContainer::destroyIterator(const void *iterator) const

Destroys a non-const iterator previously created using begin() or end().

See also begin(), end(), and destroyConstIterator().

### qsizetype QMetaContainer::diffConstIterator(const void *i, const void *j) const

Returns the distance between the const iterators i and j, the equivalent of i `-` j. If j is closer to the end of the container than i, the returned value is negative. The behavior is unspecified in this case if hasBidirectionalIterator() returns false.

See also constBegin() and constEnd().

### qsizetype QMetaContainer::diffIterator(const void *i, const void *j) const

Returns the distance between the non-const iterators i and j, the equivalent of i `-` j. If j is closer to the end of the container than i, the returned value is negative. The behavior is unspecified in this case if hasBidirectionalIterator() returns false.

See also begin() and end().

### void *QMetaContainer::end(void *container) const

Creates and returns a non-const iterator pointing to the end of container. The iterator is allocated on the heap using new. It has to be destroyed using destroyIterator eventually, to reclaim the memory.

Returns `nullptr` if the container doesn't offer any non-const iterators.

See also hasIterator(), begin(), constBegin(), constEnd(), and destroyIterator().

### bool QMetaContainer::hasBidirectionalIterator() const

Returns `true` if the underlying container provides a bi-directional iterator or a random access iterator as defined by std::bidirectional_iterator_tag and std::random_access_iterator_tag, respectively. Otherwise returns `false`.

QMetaSequence assumes that const and non-const iterators for the same container have the same iterator traits.

### bool QMetaContainer::hasConstIterator() const

Returns `true` if the underlying container offers a const iterator, `false` otherwise.

See also constBegin(), constEnd(), destroyConstIterator(), compareConstIterator(), diffConstIterator(), advanceConstIterator(), and copyConstIterator().

### bool QMetaContainer::hasForwardIterator() const

Returns `true` if the underlying container provides at least a forward iterator as defined by std::forward_iterator_tag, otherwise returns `false`. Bi-directional iterators and random access iterators are specializations of forward iterators. This method will also return `true` if the container provides one of those.

QMetaSequence assumes that const and non-const iterators for the same container have the same iterator traits.

### bool QMetaContainer::hasInputIterator() const

Returns `true` if the underlying container provides at least an input iterator as defined by std::input_iterator_tag, otherwise returns `false`. Forward, Bi-directional, and random access iterators are specializations of input iterators. This method will also return `true` if the container provides one of those.

QMetaSequence assumes that const and non-const iterators for the same container have the same iterator traits.

### bool QMetaContainer::hasIterator() const

Returns `true` if the underlying container offers a non-const iterator, `false` otherwise.

See also begin(), end(), destroyIterator(), compareIterator(), diffIterator(), advanceIterator(), and copyIterator().

### bool QMetaContainer::hasRandomAccessIterator() const

Returns `true` if the underlying container provides a random access iterator as defined by std::random_access_iterator_tag, otherwise returns `false`.

QMetaSequence assumes that const and non-const iterators for the same container have the same iterator traits.

### bool QMetaContainer::hasSize() const

Returns `true` if the container can be queried for its size, `false` otherwise.

See also size().

### qsizetype QMetaContainer::size(const void *container) const

Returns the number of values in the given container if it can be queried for its size. Otherwise returns `-1`.

See also hasSize().