Qt 5.11 | Qt Core | C++ Classes | iterator

Qt 5.11.3 Reference Documentation

# iterator Class

(QJsonObject::iterator)

The QJsonObject::iterator class provides an STL-style non-const iterator for QJsonObject. More...

Header: | #include <iterator>
qmake: | QT += core
Since: | Qt 5.0

- List of all members, including inherited members

## Public Types

typedef | iterator_category

## Public Functions

| iterator()
QString | key() const
QJsonValueRef | value() const
bool | operator!=(const iterator &other) const
bool | operator!=(const const_iterator &other) const
QJsonValueRef | operator*() const
iterator | operator+(int j) const
iterator & | operator++()
iterator | operator++(int)
iterator & | operator+=(int j)
iterator | operator-(int j) const
iterator & | operator--()
iterator | operator--(int)
iterator & | operator-=(int j)
QJsonValueRef * | operator->() const
bool | operator==(const iterator &other) const
bool | operator==(const const_iterator &other) const

## Detailed Description

The QJsonObject::iterator class provides an STL-style non-const iterator for QJsonObject.

QJsonObject::iterator allows you to iterate over a QJsonObject and to modify the value (but not the key) stored under a particular key. If you want to iterate over a const QJsonObject, you should use QJsonObject::const_iterator. It is generally good practice to use QJsonObject::const_iterator on a non-const QJsonObject as well, unless you need to change the QJsonObject through the iterator. Const iterators are slightly faster, and improve code readability.

The default QJsonObject::iterator constructor creates an uninitialized iterator. You must initialize it using a QJsonObject function like QJsonObject::begin(), QJsonObject::end(), or QJsonObject::find() before you can start iterating.

Multiple iterators can be used on the same object. Existing iterators will however become dangling once the object gets modified.

See also QJsonObject::const_iterator, JSON Support in Qt, and JSON Save Game Example.

## Member Type Documentation

### typedef iterator::iterator_category

A synonym for std::random_access_iterator_tag indicating this iterator is a random-access iterator.

Note: In Qt versions before 5.6, this was set by mistake to std::bidirectional_iterator_tag.

## Member Function Documentation

### bool iterator::operator!=(const iterator &other) const

### bool iterator::operator!=(const const_iterator &other) const

Returns `true` if other points to a different item than this iterator; otherwise returns `false`.

See also operator==().

### bool iterator::operator==(const iterator &other) const

### bool iterator::operator==(const const_iterator &other) const

Returns `true` if other points to the same item as this iterator; otherwise returns `false`.

See also operator!=().

### iterator::iterator()

Constructs an uninitialized iterator.

Functions like key(), value(), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.

See also QJsonObject::begin() and QJsonObject::end().

### QString iterator::key() const

Returns the current item's key.

There is no direct way of changing an item's key through an iterator, although it can be done by calling QJsonObject::erase() followed by QJsonObject::insert().

See also value().

### QJsonValueRef iterator::value() const

Returns a modifiable reference to the current item's value.

You can change the value of an item by using value() on the left side of an assignment.

The return value is of type QJsonValueRef, a helper class for QJsonArray and QJsonObject. When you get an object of type QJsonValueRef, you can use it as if it were a reference to a QJsonValue. If you assign to it, the assignment will apply to the element in the QJsonArray or QJsonObject from which you got the reference.

See also key() and operator*().

### QJsonValueRef iterator::operator*() const

Returns a modifiable reference to the current item's value.

Same as value().

The return value is of type QJsonValueRef, a helper class for QJsonArray and QJsonObject. When you get an object of type QJsonValueRef, you can use it as if it were a reference to a QJsonValue. If you assign to it, the assignment will apply to the element in the QJsonArray or QJsonObject from which you got the reference.

See also key().

### iterator iterator::operator+(int j) const

Returns an iterator to the item at j positions forward from this iterator. If j is negative, the iterator goes backward.

See also operator-().

### iterator &iterator::operator++()

The prefix ++ operator, `++i`, advances the iterator to the next item in the object and returns an iterator to the new current item.

Calling this function on QJsonObject::end() leads to undefined results.

See also operator--().

### iterator iterator::operator++(int)

This is an overloaded function.

The postfix ++ operator, `i++`, advances the iterator to the next item in the object and returns an iterator to the previously current item.

### iterator &iterator::operator+=(int j)

Advances the iterator by j items. If j is negative, the iterator goes backward.

See also operator-=() and operator+().

### iterator iterator::operator-(int j) const

Returns an iterator to the item at j positions backward from this iterator. If j is negative, the iterator goes forward.

See also operator+().

### iterator &iterator::operator--()

The prefix -- operator, `--i`, makes the preceding item current and returns an iterator pointing to the new current item.

Calling this function on QJsonObject::begin() leads to undefined results.

See also operator++().

### iterator iterator::operator--(int)

This is an overloaded function.

The postfix -- operator, `i--`, makes the preceding item current and returns an iterator pointing to the previously current item.

### iterator &iterator::operator-=(int j)

Makes the iterator go back by j items. If j is negative, the iterator goes forward.

See also operator+=() and operator-().

### QJsonValueRef *iterator::operator->() const

Returns a pointer to a modifiable reference to the current item.