- Qt 5.15
- Qt Core
- Obsolete Members for <QtAlgorithms>
- Qt 5.15.18 Reference Documentation

# Obsolete Members for <QtAlgorithms>

The following members of class <QtAlgorithms> are obsolete. They are provided to keep old source code working. We strongly advise against using them in new code.

## Functions

`(obsolete)` RandomAccessIterator | qBinaryFind(RandomAccessIterator begin, RandomAccessIterator end, const T &value)
`(obsolete)` RandomAccessIterator | qBinaryFind(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)
`(obsolete)` typename Container::const_iterator | qBinaryFind(const Container &container, const T &value)
`(obsolete)` OutputIterator | qCopy(InputIterator begin1, InputIterator end1, OutputIterator begin2)
`(obsolete)` BiIterator2 | qCopyBackward(BiIterator1 begin1, BiIterator1 end1, BiIterator2 end2)
`(obsolete)` void | qCount(InputIterator begin, InputIterator end, const T &value, Size &n)
`(obsolete)` void | qCount(const Container &container, const T &value, Size &n)
`(obsolete)` bool | qEqual(InputIterator1 begin1, InputIterator1 end1, InputIterator2 begin2)
`(obsolete)` void | qFill(ForwardIterator begin, ForwardIterator end, const T &value)
`(obsolete)` void | qFill(Container &container, const T &value)
`(obsolete)` InputIterator | qFind(InputIterator begin, InputIterator end, const T &value)
`(obsolete)` typename Container::const_iterator | qFind(const Container &container, const T &value)
`(obsolete)` LessThan | qGreater()
`(obsolete)` LessThan | qLess()
`(obsolete)` RandomAccessIterator | qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)
`(obsolete)` RandomAccessIterator | qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)
`(obsolete)` typename Container::const_iterator | qLowerBound(const Container &container, const T &value)
`(obsolete)` void | qSort(RandomAccessIterator begin, RandomAccessIterator end)
`(obsolete)` void | qSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)
`(obsolete)` void | qSort(Container &container)
`(obsolete)` void | qStableSort(RandomAccessIterator begin, RandomAccessIterator end)
`(obsolete)` void | qStableSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)
`(obsolete)` void | qStableSort(Container &container)
`(obsolete)` RandomAccessIterator | qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)
`(obsolete)` RandomAccessIterator | qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)
`(obsolete)` typename Container::const_iterator | qUpperBound(const Container &container, const T &value)

## Function Documentation

### template <typename RandomAccessIterator, typename T> RandomAccessIterator qBinaryFind(RandomAccessIterator begin, RandomAccessIterator end, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::binary_search` or `std::lower_bound` instead.

Performs a binary search of the range [begin, end) and returns the position of an occurrence of value. If there are no occurrences of value, returns end.

The items in the range [begin, end) must be sorted in ascending order; see qSort().

If there are many occurrences of the same value, any one of them could be returned. Use qLowerBound() or qUpperBound() if you need finer control.

Example:

     QVector<int> vect;
     vect << 3 << 3 << 6 << 6 << 6 << 8;

     QVector<int>::iterator i =
             qBinaryFind(vect.begin(), vect.end(), 6);
     // i == vect.begin() + 2 (or 3 or 4)

This function requires the item type (in the example above, QString) to implement `operator<()`.

See also qLowerBound(), qUpperBound(), and random access iterators.

### template <typename RandomAccessIterator, typename T, typename LessThan> RandomAccessIterator qBinaryFind(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::binary_search` or `std::lower_bound` instead.

Uses the lessThan function instead of `operator<()` to compare the items.

Note that the items in the range must be sorted according to the order specified by the lessThan object.

### template <typename Container, typename T> typename Container::const_iterator qBinaryFind(const Container &container, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::binary_search` or `std::lower_bound` instead.

This is the same as qBinaryFind(container.begin(), container.end(), value);

### template <typename InputIterator, typename OutputIterator> OutputIterator qCopy(InputIterator begin1, InputIterator end1, OutputIterator begin2)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::copy` instead.

Copies the items from range [begin1, end1) to range [begin2, ...), in the order in which they appear.

The item at position begin1 is assigned to that at position begin2; the item at position begin1 + 1 is assigned to that at position begin2 + 1; and so on.

Example:

     QStringList list;
     list << "one" << "two" << "three";

     QVector<QString> vect1(3);
     qCopy(list.begin(), list.end(), vect1.begin());
     // vect: [ "one", "two", "three" ]

     QVector<QString> vect2(8);
     qCopy(list.begin(), list.end(), vect2.begin() + 2);
     // vect: [ "", "", "one", "two", "three", "", "", "" ]

See also qCopyBackward(), input iterators, and output iterators.

### template <typename BiIterator1, typename BiIterator2> BiIterator2 qCopyBackward(BiIterator1 begin1, BiIterator1 end1, BiIterator2 end2)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::copy_backward` instead.

Copies the items from range [begin1, end1) to range [..., end2).

The item at position end1 - 1 is assigned to that at position end2 - 1; the item at position end1 - 2 is assigned to that at position end2 - 2; and so on.

Example:

     QStringList list;
     list << "one" << "two" << "three";

     QVector<QString> vect(5);
     qCopyBackward(list.begin(), list.end(), vect.end());
     // vect: [ "", "", "one", "two", "three" ]

See also qCopy() and bidirectional iterators.

### template <typename InputIterator, typename T, typename Size> void qCount(InputIterator begin, InputIterator end, const T &value, Size &n)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::count` instead.

Returns the number of occurrences of value in the range [begin, end), which is returned in n. n is never initialized, the count is added to n. It is the caller's responsibility to initialize n.

Example:

     QList<int> list;
     list << 3 << 3 << 6 << 6 << 6 << 8;

     int countOf6 = 0;
     qCount(list.begin(), list.end(), 6, countOf6);
     // countOf6 == 3

     int countOf7 = 0;
     qCount(list.begin(), list.end(), 7, countOf7);
     // countOf7 == 0

This function requires the item type (in the example above, `int`) to implement `operator==()`.

See also input iterators.

### template <typename Container, typename T, typename Size> void qCount(const Container &container, const T &value, Size &n)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::count` instead.

Instead of operating on iterators, as in the other overload, this function operates on the specified container to obtain the number of instances of value in the variable passed as a reference in argument n.

### template <typename InputIterator1, typename InputIterator2> bool qEqual(InputIterator1 begin1, InputIterator1 end1, InputIterator2 begin2)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::equal` instead.

Compares the items in the range [begin1, end1) with the items in the range [begin2, ...). Returns `true` if all the items compare equal; otherwise returns `false`.

Example:

     QStringList list;
     list << "one" << "two" << "three";

     QVector<QString> vect(3);
     vect[0] = "one";
     vect[1] = "two";
     vect[2] = "three";

     bool ret1 = qEqual(list.begin(), list.end(), vect.begin());
     // ret1 == true

     vect[2] = "seven";
     bool ret2 = qEqual(list.begin(), list.end(), vect.begin());
     // ret2 == false

This function requires the item type (in the example above, QString) to implement `operator==()`.

See also input iterators.

### template <typename ForwardIterator, typename T> void qFill(ForwardIterator begin, ForwardIterator end, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::fill` instead.

Fills the range [begin, end) with value.

Example:

     QStringList list;
     list << "one" << "two" << "three";

     qFill(list.begin(), list.end(), "eleven");
     // list: [ "eleven", "eleven", "eleven" ]

     qFill(list.begin() + 1, list.end(), "six");
     // list: [ "eleven", "six", "six" ]

See also qCopy() and forward iterators.

### template <typename Container, typename T> void qFill(Container &container, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::fill` instead.

This is the same as qFill(container.begin(), container.end(), value);

### template <typename InputIterator, typename T> InputIterator qFind(InputIterator begin, InputIterator end, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::find` instead.

Returns an iterator to the first occurrence of value in a container in the range [begin, end). Returns end if value isn't found.

Example:

     QStringList list;
     list << "one" << "two" << "three";

     QStringList::iterator i1 = qFind(list.begin(), list.end(), "two");
     // i1 == list.begin() + 1

     QStringList::iterator i2 = qFind(list.begin(), list.end(), "seventy");
     // i2 == list.end()

This function requires the item type (in the example above, QString) to implement `operator==()`.

If the items in the range are in ascending order, you can get faster results by using qLowerBound() or qBinaryFind() instead of qFind().

See also qBinaryFind() and input iterators.

### template <typename Container, typename T> typename Container::const_iterator qFind(const Container &container, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::find` instead.

This is the same as qFind(container.constBegin(), container.constEnd(), value);

### template <typename T> LessThan qGreater()

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::greater` instead.

Returns a functional object, or functor, that can be passed to qSort() or qStableSort().

Example:

     QList<int> list;
     list << 33 << 12 << 68 << 6 << 12;
     qSort(list.begin(), list.end(), qGreater<int>());
     // list: [ 68, 33, 12, 12, 6 ]

See also qLess<T>().

### template <typename T> LessThan qLess()

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::less` instead.

Returns a functional object, or functor, that can be passed to qSort() or qStableSort().

Example:

     QList<int> list;
     list << 33 << 12 << 68 << 6 << 12;
     qSort(list.begin(), list.end(), qLess<int>());
     // list: [ 6, 12, 12, 33, 68 ]

See also qGreater<T>().

### template <typename RandomAccessIterator, typename T> RandomAccessIterator qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::lower_bound` instead.

Performs a binary search of the range [begin, end) and returns the position of the first occurrence of value. If no such item is found, returns the position where it should be inserted.

The items in the range [begin, end) must be sorted in ascending order; see qSort().

Example:

     QList<int> list;
     list << 3 << 3 << 6 << 6 << 6 << 8;

     QList<int>::iterator i = qLowerBound(list.begin(), list.end(), 5);
     list.insert(i, 5);
     // list: [ 3, 3, 5, 6, 6, 6, 8 ]

     i = qLowerBound(list.begin(), list.end(), 12);
     list.insert(i, 12);
     // list: [ 3, 3, 5, 6, 6, 6, 8, 12 ]

This function requires the item type (in the example above, `int`) to implement `operator<()`.

qLowerBound() can be used in conjunction with qUpperBound() to iterate over all occurrences of the same value:

     QVector<int> vect;
     vect << 3 << 3 << 6 << 6 << 6 << 8;
     QVector<int>::iterator begin6 =
             qLowerBound(vect.begin(), vect.end(), 6);
     QVector<int>::iterator end6 =
             qUpperBound(begin6, vect.end(), 6);

     QVector<int>::iterator i = begin6;
     while (i != end6) {
         *i = 7;
         ++i;
     }
     // vect: [ 3, 3, 7, 7, 7, 8 ]

See also qUpperBound() and qBinaryFind().

### template <typename RandomAccessIterator, typename T, typename LessThan> RandomAccessIterator qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::lower_bound` instead.

Uses the lessThan function instead of `operator<()` to compare the items.

Note that the items in the range must be sorted according to the order specified by the lessThan object.

### template <typename Container, typename T> typename Container::const_iterator qLowerBound(const Container &container, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::lower_bound` instead.

For read-only iteration over containers, this function is broadly equivalent to qLowerBound(container.begin(), container.end(), value). However, since it returns a const iterator, you cannot use it to modify the container; for example, to insert items.

### template <typename RandomAccessIterator> void qSort(RandomAccessIterator begin, RandomAccessIterator end)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::sort` instead.

Sorts the items in range [begin, end) in ascending order using the quicksort algorithm.

Example:

     QList<int> list;
     list << 33 << 12 << 68 << 6 << 12;
     qSort(list.begin(), list.end());
     // list: [ 6, 12, 12, 33, 68 ]

The sort algorithm is efficient on large data sets. It operates in linear-logarithmic time, O(n log n).

This function requires the item type (in the example above, `int`) to implement `operator<()`.

If neither of the two items is "less than" the other, the items are taken to be equal. It is then undefined which one of the two items will appear before the other after the sort.

See also qStableSort() and random access iterators.

### template <typename RandomAccessIterator, typename LessThan> void qSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::sort` instead.

Uses the lessThan function instead of `operator<()` to compare the items.

For example, here's how to sort the strings in a QStringList in case-insensitive alphabetical order:

     bool caseInsensitiveLessThan(const QString &s1, const QString &s2)
     {
         return s1.toLower() < s2.toLower();
     }

     int doSomething()
     {
         QStringList list;
         list << "AlPha" << "beTA" << "gamma" << "DELTA";
         qSort(list.begin(), list.end(), caseInsensitiveLessThan);
         // list: [ "AlPha", "beTA", "DELTA", "gamma" ]
     }

To sort values in reverse order, pass qGreater<T>() as the lessThan parameter. For example:

     QList<int> list;
     list << 33 << 12 << 68 << 6 << 12;
     qSort(list.begin(), list.end(), qGreater<int>());
     // list: [ 68, 33, 12, 12, 6 ]

If neither of the two items is "less than" the other, the items are taken to be equal. It is then undefined which one of the two items will appear before the other after the sort.

An alternative to using qSort() is to put the items to sort in a QMap, using the sort key as the QMap key. This is often more convenient than defining a lessThan function. For example, the following code shows how to sort a list of strings case insensitively using QMap:

     QStringList list;
     list << "AlPha" << "beTA" << "gamma" << "DELTA";

     QMap<QString, QString> map;
     foreach (const QString &str, list)
         map.insert(str.toLower(), str);

     list = map.values();

See also QMap.

### template <typename Container> void qSort(Container &container)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::sort` instead.

This is the same as qSort(container.begin(), container.end());

### template <typename RandomAccessIterator> void qStableSort(RandomAccessIterator begin, RandomAccessIterator end)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::stable_sort` instead.

Sorts the items in range [begin, end) in ascending order using a stable sorting algorithm.

If neither of the two items is "less than" the other, the items are taken to be equal. The item that appeared before the other in the original container will still appear first after the sort. This property is often useful when sorting user-visible data.

Example:

     QList<int> list;
     list << 33 << 12 << 68 << 6 << 12;
     qStableSort(list.begin(), list.end());
     // list: [ 6, 12, 12, 33, 68 ]

The sort algorithm is efficient on large data sets. It operates in linear-logarithmic time, O(n log n).

This function requires the item type (in the example above, `int`) to implement `operator<()`.

See also qSort() and random access iterators.

### template <typename RandomAccessIterator, typename LessThan> void qStableSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::stable_sort` instead.

Uses the lessThan function instead of `operator<()` to compare the items.

For example, here's how to sort the strings in a QStringList in case-insensitive alphabetical order:

     bool caseInsensitiveLessThan(const QString &s1, const QString &s2)
     {
         return s1.toLower() < s2.toLower();
     }

     int doSomething()
     {
         QStringList list;
         list << "AlPha" << "beTA" << "gamma" << "DELTA";
         qStableSort(list.begin(), list.end(), caseInsensitiveLessThan);
         // list: [ "AlPha", "beTA", "DELTA", "gamma" ]
     }

Note that earlier versions of Qt allowed using a lessThan function that took its arguments by non-const reference. From 4.3 and on this is no longer possible, the arguments has to be passed by const reference or value.

To sort values in reverse order, pass qGreater<T>() as the lessThan parameter. For example:

     QList<int> list;
     list << 33 << 12 << 68 << 6 << 12;
     qStableSort(list.begin(), list.end(), qGreater<int>());
     // list: [ 68, 33, 12, 12, 6 ]

If neither of the two items is "less than" the other, the items are taken to be equal. The item that appeared before the other in the original container will still appear first after the sort. This property is often useful when sorting user-visible data.

### template <typename Container> void qStableSort(Container &container)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::stable_sort` instead.

This is the same as qStableSort(container.begin(), container.end());

### template <typename RandomAccessIterator, typename T> RandomAccessIterator qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

Use `std::upper_bound` instead.

Performs a binary search of the range [begin, end) and returns the position of the one-past-the-last occurrence of value. If no such item is found, returns the position where the item should be inserted.

The items in the range [begin, end) must be sorted in ascending order; see qSort().

Example:

     QList<int> list;
     list << 3 << 3 << 6 << 6 << 6 << 8;

     QList<int>::iterator i = qUpperBound(list.begin(), list.end(), 5);
     list.insert(i, 5);
     // list: [ 3, 3, 5, 6, 6, 6, 8 ]

     i = qUpperBound(list.begin(), list.end(), 12);
     list.insert(i, 12);
     // list: [ 3, 3, 5, 6, 6, 6, 8, 12 ]

This function requires the item type (in the example above, `int`) to implement `operator<()`.

qUpperBound() can be used in conjunction with qLowerBound() to iterate over all occurrences of the same value:

     QVector<int> vect;
     vect << 3 << 3 << 6 << 6 << 6 << 8;
     QVector<int>::iterator begin6 =
             qLowerBound(vect.begin(), vect.end(), 6);
     QVector<int>::iterator end6 =
             qUpperBound(vect.begin(), vect.end(), 6);

     QVector<int>::iterator i = begin6;
     while (i != end6) {
         *i = 7;
         ++i;
     }
     // vect: [ 3, 3, 7, 7, 7, 8 ]

See also qLowerBound() and qBinaryFind().

### template <typename RandomAccessIterator, typename T, typename LessThan> RandomAccessIterator qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::upper_bound` instead.

Uses the lessThan function instead of `operator<()` to compare the items.

Note that the items in the range must be sorted according to the order specified by the lessThan object.

### template <typename Container, typename T> typename Container::const_iterator qUpperBound(const Container &container, const T &value)

This function is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This is an overloaded function.

Use `std::upper_bound` instead.

This is the same as qUpperBound(container.begin(), container.end(), value);