binary_search (3C++std) - Tru64 UNIX
Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc.
NAME
binary_search - Performs a binary search for a value on a container.
SYNOPSIS
#include <algorithm>
template <class ForwardIterator, class T>
bool
binary_search(ForwardIterator first, ForwardIterator last,
const T& value);
template <class ForwardIterator, class T, class Compare>
bool
binary_search(ForwardIterator first, ForwardIterator last,
const T& value, Compare comp);
DESCRIPTION
The binary_search algorithm, like other related algorithms (equal_range,
lower_bound and upper_bound) performs a binary search on ordered
containers. All binary search algorithms have two versions. The first
version uses the less than operator (operator<) to perform the comparison,
and assumes that the sequence has been sorted using that operator. The
second version allows you to include a function object of type Compare,
which it assumes was the function used to sort the sequence. The function
object must be a binary predicate.
The binary_search algorithm returns true if a sequence contains an element
equivalent to the argument value. The first version of binary_search
returns true if the sequence contains at least one element that is equal to
the search value. The second version of the binary_search algorithm
returns true if the sequence contains at least one element that satisfies
the conditions of the comparison function. Formally, binary_search returns
true if there is an iterator i in the range [first, last) that satisfies
the corresponding conditions:
!(*i < value) && !(value < *i)
or
comp(*i, value) == false && comp(value, *i) == false
COMPLEXITY
binary_search performs at most log(last - first) + 2 comparisons.
EXAMPLE
//
// b_search.cpp
//
#include <vector>
#include <algorithm>
#include <iostream.h>
int main()
{
typedef vector<int>::iterator iterator;
int d1[10] = {0,1,2,2,3,4,2,2,6,7};
//
// Set up a vector
//
vector<int> v1(d1,d1 + 10);
//
// Try binary_search variants
//
sort(v1.begin(),v1.end());
bool b1 = binary_search(v1.begin(),v1.end(),3);
bool b2 =
binary_search(v1.begin(),v1.end(),11,less<int>());
//
// Output results
//
cout << "In the vector: ";
copy(v1.begin(),v1.end(),
ostream_iterator<int,char>(cout," "));
cout << endl << "The number 3 was "
<< (b1 ? "FOUND" : "NOT FOUND");
cout << endl << "The number 11 was "
<< (b2 ? "FOUND" : "NOT FOUND") << endl;
return 0;
}
Output :
In the vector: 0 1 2 2 2 2 3 4 6 7
The number 3 was FOUND
The number 11 was NOT FOUND
WARNINGS
If your compiler does not support default template parameters, then you
need to always supply the Allocator template argument. For instance,
you'll have to write:
vector<int,allocator<int> >
instead of:
vector<int>
SEE ALSO
equal_range, lower_bound, upper_bound
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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