Binary Search

Collaboration diagram for Binary Search:

Functions
template<typename _ForwardIterator , typename _Tp >
constexpr bool	std::binary_search (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val)
template<typename _ForwardIterator , typename _Tp , typename _Compare >
constexpr bool	std::binary_search (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val, _Compare __comp)
template<typename _ForwardIterator , typename _Tp >
constexpr pair< _ForwardIterator, _ForwardIterator >	std::equal_range (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val)
template<typename _ForwardIterator , typename _Tp , typename _Compare >
constexpr pair< _ForwardIterator, _ForwardIterator >	std::equal_range (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val, _Compare __comp)
template<typename _ForwardIterator , typename _Tp >
constexpr _ForwardIterator	std::lower_bound (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val)
template<typename _ForwardIterator , typename _Tp , typename _Compare >
constexpr _ForwardIterator	std::lower_bound (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val, _Compare __comp)
template<typename _ForwardIterator , typename _Tp >
constexpr _ForwardIterator	std::upper_bound (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val)
template<typename _ForwardIterator , typename _Tp , typename _Compare >
constexpr _ForwardIterator	std::upper_bound (_ForwardIterator __first, _ForwardIterator __last, const _Tp &__val, _Compare __comp)

Detailed Description

These algorithms are variations of a classic binary search, and all assume that the sequence being searched is already sorted.

The number of comparisons will be logarithmic (and as few as possible). The number of steps through the sequence will be logarithmic for random-access iterators (e.g., pointers), and linear otherwise.

The LWG has passed Defect Report 270, which notes: The proposed resolution reinterprets binary search. Instead of thinking about searching for a value in a sorted range, we view that as an important special case of a more general algorithm: searching for the partition point in a partitioned range. We also add a guarantee that the old wording did not: we ensure that the upper bound is no earlier than the lower bound, that the pair returned by equal_range is a valid range, and that the first part of that pair is the lower bound.

The actual effect of the first sentence is that a comparison functor passed by the user doesn't necessarily need to induce a strict weak ordering relation. Rather, it partitions the range.

Function Documentation

binary_search() [1/2]

template<typename _ForwardIterator , typename _Tp >

constexpr bool std::binary_search ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val  )

constexpr

Determines whether an element exists in a range.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.

Returns

True if __val (or its equivalent) is in [__first,__last ].

Note that this does not actually return an iterator to __val. For that, use std::find or a container's specialized find member functions.

Definition at line 2225 of file stl_algo.h.

binary_search() [2/2]

template<typename _ForwardIterator , typename _Tp , typename _Compare >

constexpr bool std::binary_search ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val, _Compare  __comp  )

constexpr

Determines whether an element exists in a range.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.
__comp	A functor to use for comparisons.

Returns

True if __val (or its equivalent) is in [__first,__last].

Note that this does not actually return an iterator to __val. For that, use std::find or a container's specialized find member functions.

The comparison function should have the same effects on ordering as the function used for the initial sort.

Definition at line 2259 of file stl_algo.h.

equal_range() [1/2]

template<typename _ForwardIterator , typename _Tp >

constexpr pair<_ForwardIterator, _ForwardIterator> std::equal_range ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val  )

inlineconstexpr

Finds the largest subrange in which __val could be inserted at any place in it without changing the ordering.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.

Returns

An pair of iterators defining the subrange.

This is equivalent to

std::make_pair(lower_bound(__first, __last, __val),
               upper_bound(__first, __last, __val))

but does not actually call those functions.

Definition at line 2154 of file stl_algo.h.

equal_range() [2/2]

template<typename _ForwardIterator , typename _Tp , typename _Compare >

constexpr pair<_ForwardIterator, _ForwardIterator> std::equal_range ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val, _Compare  __comp  )

inlineconstexpr

Finds the largest subrange in which __val could be inserted at any place in it without changing the ordering.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.
__comp	A functor to use for comparisons.

Returns

An pair of iterators defining the subrange.

This is equivalent to

std::make_pair(lower_bound(__first, __last, __val, __comp),
               upper_bound(__first, __last, __val, __comp))

but does not actually call those functions.

Definition at line 2191 of file stl_algo.h.

lower_bound() [1/2]

template<typename _ForwardIterator , typename _Tp >

constexpr _ForwardIterator std::lower_bound ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val  )

inlineconstexpr

Finds the first position in which val could be inserted without changing the ordering.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.

Returns

An iterator pointing to the first element not less than val, or end() if every element is less than val.

Definition at line 1489 of file stl_algobase.h.

lower_bound() [2/2]

template<typename _ForwardIterator , typename _Tp , typename _Compare >

constexpr _ForwardIterator std::lower_bound ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val, _Compare  __comp  )

inlineconstexpr

Finds the first position in which __val could be inserted without changing the ordering.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.
__comp	A functor to use for comparisons.

Returns

An iterator pointing to the first element not less than __val, or end() if every element is less than __val.

The comparison function should have the same effects on ordering as the function used for the initial sort.

Definition at line 1994 of file stl_algo.h.

upper_bound() [1/2]

template<typename _ForwardIterator , typename _Tp >

constexpr _ForwardIterator std::upper_bound ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val  )

inlineconstexpr

Finds the last position in which __val could be inserted without changing the ordering.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.

Returns

An iterator pointing to the first element greater than __val, or end() if no elements are greater than __val.

Definition at line 2050 of file stl_algo.h.

upper_bound() [2/2]

template<typename _ForwardIterator , typename _Tp , typename _Compare >

constexpr _ForwardIterator std::upper_bound ( _ForwardIterator  __first, _ForwardIterator  __last, const _Tp &  __val, _Compare  __comp  )

inlineconstexpr

Finds the last position in which __val could be inserted without changing the ordering.

Parameters

__first	An iterator.
__last	Another iterator.
__val	The search term.
__comp	A functor to use for comparisons.

Returns

An iterator pointing to the first element greater than __val, or end() if no elements are greater than __val.

The comparison function should have the same effects on ordering as the function used for the initial sort.

Definition at line 2081 of file stl_algo.h.