QList Class

QList<int> integerList;
QList<QDate> dateList;

QList<QString> list = { "one", "two", "three" };

list << "four" << "five";

if (list[0] == "Bob")
    list[0] = "Robert";

for (int i = 0; i < list.size(); ++i) {
    if (list.at(i) == "Jane")
        cout << "Found Jane at position " << i << endl;
}

QList<QWidget *> list;
...
while (!list.isEmpty())
    delete list.takeFirst();

int i = list.indexOf("Jane");
if (i != -1)
    cout << "First occurrence of Jane is at position " << i << endl;

Member Function Documentation

QList::QList()

Constructs an empty list.

QList::QList(const QList<T> &other)

Constructs a copy of other.

This operation takes constant time, because QList is implicitly shared. This makes returning a QList from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes linear time.

See also operator=().

QList::QList(QList<T> &&other)

Move-constructs a QList instance, making it point at the same object that other was pointing to.

This function was introduced in Qt 5.2.

QList::QList(int args)

Construct a list from the std::initializer_list specified by args.

This constructor is only enabled if the compiler supports C++11 initializer lists.

This function was introduced in Qt 4.8.

QList::~QList()

Destroys the list. References to the values in the list and all iterators of this list become invalid.

void QList::append(const T &value)

Inserts value at the end of the list.

Example:

QList<QString> list;
list.append("one");
list.append("two");
list.append("three");
// list: ["one", "two", "three"]

This is the same as list.insert(size(), value).

If this list is not shared, this operation is typically very fast (amortized constant time), because QList preallocates extra space on both sides of its internal buffer to allow for fast growth at both ends of the list.

See also operator<<(), prepend(), and insert().

void QList::append(const QList<T> &value)

This is an overloaded function.

Appends the items of the value list to this list.

This function was introduced in Qt 4.5.

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

const T &QList::at(int i) const

Returns the item at index position i in the list. i must be a valid index position in the list (i.e., 0 <= i < size()).

This function is very fast (constant time).

See also value() and operator[]().

T &QList::back()

This function is provided for STL compatibility. It is equivalent to last(). The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

const T &QList::back() const

This is an overloaded function.

QList::iterator QList::begin()

Returns an STL-style iterator pointing to the first item in the list.

See also constBegin() and end().

QList::const_iterator QList::begin() const

This is an overloaded function.

QList::const_iterator QList::cbegin() const

Returns a const STL-style iterator pointing to the first item in the list.

This function was introduced in Qt 5.0.

See also begin() and cend().

QList::const_iterator QList::cend() const

Returns a const STL-style iterator pointing to the imaginary item after the last item in the list.

This function was introduced in Qt 5.0.

See also cbegin() and end().

void QList::clear()

Removes all items from the list.

See also removeAll().

QList::const_iterator QList::constBegin() const

Returns a const STL-style iterator pointing to the first item in the list.

See also begin() and constEnd().

QList::const_iterator QList::constEnd() const

Returns a const STL-style iterator pointing to the imaginary item after the last item in the list.

See also constBegin() and end().

const T &QList::constFirst() const

Returns a const reference to the first item in the list. The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

This function was introduced in Qt 5.6.

See also constLast(), isEmpty(), and first().

const T &QList::constLast() const

Returns a reference to the last item in the list. The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

This function was introduced in Qt 5.6.

See also constFirst(), isEmpty(), and last().

bool QList::contains(const T &value) const

Returns true if the list contains an occurrence of value; otherwise returns false.

This function requires the value type to have an implementation of operator==().

See also indexOf() and count().

int QList::count(const T &value) const

Returns the number of occurrences of value in the list.

This function requires the value type to have an implementation of operator==().

See also contains() and indexOf().

int QList::count() const

Returns the number of items in the list. This is effectively the same as size().

QList::const_reverse_iterator QList::crbegin() const

Returns a const STL-style reverse iterator pointing to the first item in the list, in reverse order.

This function was introduced in Qt 5.6.

See also begin(), rbegin(), and rend().

QList::const_reverse_iterator QList::crend() const

Returns a const STL-style reverse iterator pointing to one past the last item in the list, in reverse order.

This function was introduced in Qt 5.6.

See also end(), rend(), and rbegin().

bool QList::empty() const

This function is provided for STL compatibility. It is equivalent to isEmpty() and returns true if the list is empty.

QList::iterator QList::end()

Returns an STL-style iterator pointing to the imaginary item after the last item in the list.

See also begin() and constEnd().

QList::const_iterator QList::end() const

This is an overloaded function.

bool QList::endsWith(const T &value) const

Returns true if this list is not empty and its last item is equal to value; otherwise returns false.

This function was introduced in Qt 4.5.

See also isEmpty() and contains().

QList::iterator QList::erase(QList::iterator pos)

Removes the item associated with the iterator pos from the list, and returns an iterator to the next item in the list (which may be end()).

See also insert() and removeAt().

QList::iterator QList::erase(QList::iterator begin, QList::iterator end)

This is an overloaded function.

Removes all the items from begin up to (but not including) end. Returns an iterator to the same item that end referred to before the call.

T &QList::first()

Returns a reference to the first item in the list. The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

See also constFirst(), last(), and isEmpty().

const T &QList::first() const

This is an overloaded function.

[static] QList<T> QList::fromSet(const QSet<T> &set)

Returns a QList object with the data contained in set. The order of the elements in the QList is undefined.

Example:

QSet<int> set;
set << 20 << 30 << 40 << ... << 70;

QList<int> list = QList<int>::fromSet(set);
qSort(list);

See also fromVector(), toSet(), and QSet::toList().

[static] QList<T> QList::fromStdList(const int &list)

Returns a QList object with the data contained in list. The order of the elements in the QList is the same as in list.

Example:

std::list<double> stdlist;
list.push_back(1.2);
list.push_back(0.5);
list.push_back(3.14);

QList<double> list = QList<double>::fromStdList(stdlist);

See also toStdList() and QVector::fromStdVector().

[static] QList<T> QList::fromVector(const QVector<T> &vector)

Returns a QList object with the data contained in vector.

Example:

QVector<double> vect;
vect << 20.0 << 30.0 << 40.0 << 50.0;

QList<double> list = QVector<T>::fromVector(vect);
// list: [20.0, 30.0, 40.0, 50.0]

See also fromSet(), toVector(), and QVector::toList().

T &QList::front()

This function is provided for STL compatibility. It is equivalent to first(). The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

const T &QList::front() const

This is an overloaded function.

int QList::indexOf(const T &value, int from = ...) const

Returns the index position of the first occurrence of value in the list, searching forward from index position from. Returns -1 if no item matched.

Example:

QList<QString> list;
list << "A" << "B" << "C" << "B" << "A";
list.indexOf("B");          // returns 1
list.indexOf("B", 1);       // returns 1
list.indexOf("B", 2);       // returns 3
list.indexOf("X");          // returns -1

This function requires the value type to have an implementation of operator==().

Note that QList uses 0-based indexes, just like C++ arrays. Negative indexes are not supported with the exception of the value mentioned above.

See also lastIndexOf() and contains().

void QList::insert(int i, const T &value)

Inserts value at index position i in the list. If i <= 0, the value is prepended to the list. If i >= size(), the value is appended to the list.

Example:

QList<QString> list;
list << "alpha" << "beta" << "delta";
list.insert(2, "gamma");
// list: ["alpha", "beta", "gamma", "delta"]

See also append(), prepend(), replace(), and removeAt().

QList::iterator QList::insert(QList::iterator before, const T &value)

This is an overloaded function.

Inserts value in front of the item pointed to by the iterator before. Returns an iterator pointing at the inserted item. Note that the iterator passed to the function will be invalid after the call; the returned iterator should be used instead.

bool QList::isEmpty() const

Returns true if the list contains no items; otherwise returns false.

See also size().

T &QList::last()

Returns a reference to the last item in the list. The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

See also constLast(), first(), and isEmpty().

const T &QList::last() const

This is an overloaded function.

int QList::lastIndexOf(const T &value, int from = ...) const

Returns the index position of the last occurrence of value in the list, searching backward from index position from. If from is -1 (the default), the search starts at the last item. Returns -1 if no item matched.

Example:

QList<QString> list;
list << "A" << "B" << "C" << "B" << "A";
list.lastIndexOf("B");      // returns 3
list.lastIndexOf("B", 3);   // returns 3
list.lastIndexOf("B", 2);   // returns 1
list.lastIndexOf("X");      // returns -1

This function requires the value type to have an implementation of operator==().

Note that QList uses 0-based indexes, just like C++ arrays. Negative indexes are not supported with the exception of the value mentioned above.

See also indexOf().

int QList::length() const

This function is identical to count().

This function was introduced in Qt 4.5.

See also count().

QList<T> QList::mid(int pos, int length = -1) const

Returns a sub-list which includes elements from this list, starting at position pos. If length is -1 (the default), all elements from pos are included; otherwise length elements (or all remaining elements if there are less than length elements) are included.

void QList::move(int from, int to)

Moves the item at index position from to index position to.

Example:

QList<QString> list;
list << "A" << "B" << "C" << "D" << "E" << "F";
list.move(1, 4);
// list: ["A", "C", "D", "E", "B", "F"]

This is the same as insert(to, takeAt(from)).This function assumes that both from and to are at least 0 but less than size(). To avoid failure, test that both from and to are at least 0 and less than size().

See also swap(), insert(), and takeAt().

void QList::pop_back()

This function is provided for STL compatibility. It is equivalent to removeLast(). The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

void QList::pop_front()

This function is provided for STL compatibility. It is equivalent to removeFirst(). The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

void QList::prepend(const T &value)

Inserts value at the beginning of the list.

Example:

QList<QString> list;
list.prepend("one");
list.prepend("two");
list.prepend("three");
// list: ["three", "two", "one"]

This is the same as list.insert(0, value).

If this list is not shared, this operation is typically very fast (amortized constant time), because QList preallocates extra space on both sides of its internal buffer to allow for fast growth at both ends of the list.

See also append() and insert().

void QList::push_back(const T &value)

This function is provided for STL compatibility. It is equivalent to append(value).

void QList::push_front(const T &value)

This function is provided for STL compatibility. It is equivalent to prepend(value).

QList::reverse_iterator QList::rbegin()

Returns a STL-style reverse iterator pointing to the first item in the list, in reverse order.

This function was introduced in Qt 5.6.

See also begin(), crbegin(), and rend().

QList::const_reverse_iterator QList::rbegin() const

This is an overloaded function.

This function was introduced in Qt 5.6.

int QList::removeAll(const T &value)

Removes all occurrences of value in the list and returns the number of entries removed.

Example:

QList<QString> list;
list << "sun" << "cloud" << "sun" << "rain";
list.removeAll("sun");
// list: ["cloud", "rain"]

This function requires the value type to have an implementation of operator==().

See also removeOne(), removeAt(), takeAt(), and replace().

void QList::removeAt(int i)

Removes the item at index position i. i must be a valid index position in the list (i.e., 0 <= i < size()).

See also takeAt(), removeFirst(), removeLast(), and removeOne().

void QList::removeFirst()

Removes the first item in the list. Calling this function is equivalent to calling removeAt(0). The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

See also removeAt() and takeFirst().

void QList::removeLast()

Removes the last item in the list. Calling this function is equivalent to calling removeAt(size() - 1). The list must not be empty. If the list can be empty, call isEmpty() before calling this function.

See also removeAt() and takeLast().

bool QList::removeOne(const T &value)

Removes the first occurrence of value in the list and returns true on success; otherwise returns false.

Example:

QList<QString> list;
list << "sun" << "cloud" << "sun" << "rain";
list.removeOne("sun");
// list: ["cloud", "sun", "rain"]

This function requires the value type to have an implementation of operator==().

This function was introduced in Qt 4.4.

See also removeAll(), removeAt(), takeAt(), and replace().

QList::reverse_iterator QList::rend()

Returns a STL-style reverse iterator pointing to one past the last item in the list, in reverse order.

This function was introduced in Qt 5.6.

See also end(), crend(), and rbegin().

QList::const_reverse_iterator QList::rend() const

This is an overloaded function.

This function was introduced in Qt 5.6.

void QList::replace(int i, const T &value)

Replaces the item at index position i with value. i must be a valid index position in the list (i.e., 0 <= i < size()).

See also operator[]() and removeAt().

void QList::reserve(int alloc)

Reserve space for alloc elements.

If alloc is smaller than the current size of the list, nothing will happen.

Use this function to avoid repetetive reallocation of QList's internal data if you can predict how many elements will be appended. Note that the reservation applies only to the internal pointer array.

This function was introduced in Qt 4.7.

int QList::size() const

Returns the number of items in the list.

See also isEmpty() and count().

bool QList::startsWith(const T &value) const

Returns true if this list is not empty and its first item is equal to value; otherwise returns false.

This function was introduced in Qt 4.5.

See also isEmpty() and contains().

void QList::swap(QList<T> &other)

Swaps list other with this list. This operation is very fast and never fails.

This function was introduced in Qt 4.8.

void QList::swap(int i, int j)

Exchange the item at index position i with the item at index position j. This function assumes that both i and j are at least 0 but less than size(). To avoid failure, test that both i and j are at least 0 and less than size().

Example:

QList<QString> list;
list << "A" << "B" << "C" << "D" << "E" << "F";
list.swap(1, 4);
// list: ["A", "E", "C", "D", "B", "F"]

See also move().

T QList::takeAt(int i)

Removes the item at index position i and returns it. i must be a valid index position in the list (i.e., 0 <= i < size()).

If you don't use the return value, removeAt() is more efficient.

See also removeAt(), takeFirst(), and takeLast().

T QList::takeFirst()

Removes the first item in the list and returns it. This is the same as takeAt(0). This function assumes the list is not empty. To avoid failure, call isEmpty() before calling this function.

If this list is not shared, this operation takes constant time.

If you don't use the return value, removeFirst() is more efficient.

See also takeLast(), takeAt(), and removeFirst().

T QList::takeLast()

Removes the last item in the list and returns it. This is the same as takeAt(size() - 1). This function assumes the list is not empty. To avoid failure, call isEmpty() before calling this function.

If this list is not shared, this operation takes constant time.

If you don't use the return value, removeLast() is more efficient.

See also takeFirst(), takeAt(), and removeLast().

QSet<T> QList::toSet() const

Returns a QSet object with the data contained in this QList. Since QSet doesn't allow duplicates, the resulting QSet might be smaller than the original list was.

Example:

QStringList list;
list << "Julia" << "Mike" << "Mike" << "Julia" << "Julia";

QSet<QString> set = list.toSet();
set.contains("Julia");  // returns true
set.contains("Mike");   // returns true
set.size();             // returns 2

See also toVector(), fromSet(), and QSet::fromList().

int QList::toStdList() const

Returns a std::list object with the data contained in this QList. Example:

QList<double> list;
list << 1.2 << 0.5 << 3.14;

std::list<double> stdlist = list.toStdList();

See also fromStdList() and QVector::toStdVector().

QVector<T> QList::toVector() const

Returns a QVector object with the data contained in this QList.

Example:

QStringList list;
list << "Sven" << "Kim" << "Ola";

QVector<QString> vect = list.toVector();
// vect: ["Sven", "Kim", "Ola"]

See also toSet(), fromVector(), and QVector::fromList().

T QList::value(int i) const

Returns the value at index position i in the list.

If the index i is out of bounds, the function returns a default-constructed value. If you are certain that the index is going to be within bounds, you can use at() instead, which is slightly faster.

See also at() and operator[]().

T QList::value(int i, const T &defaultValue) const

This is an overloaded function.

If the index i is out of bounds, the function returns defaultValue.

bool QList::operator!=(const QList<T> &other) const

Returns true if other is not equal to this list; otherwise returns false.

Two lists are considered equal if they contain the same values in the same order.

This function requires the value type to have an implementation of operator==().

See also operator==().

QList<T> QList::operator+(const QList<T> &other) const

Returns a list that contains all the items in this list followed by all the items in the other list.

See also operator+=().

QList<T> &QList::operator+=(const QList<T> &other)

Appends the items of the other list to this list and returns a reference to this list.

See also operator+() and append().

QList<T> &QList::operator+=(const T &value)

This is an overloaded function.

Appends value to the list.

See also append() and operator<<().

QList<T> &QList::operator<<(const QList<T> &other)

Appends the items of the other list to this list and returns a reference to this list.

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

QList<T> &QList::operator<<(const T &value)

This is an overloaded function.

Appends value to the list.

QList<T> &QList::operator=(const QList<T> &other)

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

QList<T> &QList::operator=(QList<T> &&other)

Move-assigns other to this QList instance.

This function was introduced in Qt 5.2.

bool QList::operator==(const QList<T> &other) const

Returns true if other is equal to this list; otherwise returns false.

Two lists are considered equal if they contain the same values in the same order.

This function requires the value type to have an implementation of operator==().

See also operator!=().

T &QList::operator[](int i)

Returns the item at index position i as a modifiable reference. i must be a valid index position in the list (i.e., 0 <= i < size()).

If this function is called on a list that is currently being shared, it will trigger a copy of all elements. Otherwise, this function runs in constant time. If you do not want to modify the list you should use QList::at().

See also at() and value().

const T &QList::operator[](int i) const

This is an overloaded function.

Same as at(). This function runs in constant time.