## binary_search
## Prototype
template <class ForwardIterator, class LessThanComparable> bool binary_search(ForwardIterator first, ForwardIterator last, const LessThanComparable& value); template <class ForwardIterator, class T, class StrictWeakOrdering> bool binary_search(ForwardIterator first, ForwardIterator last, const T& value, StrictWeakOrdering comp); ## Description
Specifically, the first version returns ## DefinitionDefined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h. ## Requirements on typesFor the first version: -
`ForwardIterator` is a model of ForwardIterator. -
`LessThanComparable` is a model of LessThanComparable. -
The ordering on objects of type
`LessThanComparable` is a*strict weak ordering*, as defined in the LessThanComparable requirements. -
`ForwardIterator` 's value type is the same type as`LessThanComparable` .
For the second version: -
`ForwardIterator` is a model of ForwardIterator. -
`StrictWeakOrdering` is a model of StrictWeakOrdering. -
`ForwardIterator` 's value type is the same type as`T` . -
`ForwardIterator` 's value type is convertible to`StrictWeakOrdering` 's argument type.
## PreconditionsFor the first version: -
`[first, last)` is a valid range. -
`[first, last)` is ordered in ascending order according to`operator<` . That is, for every pair of iterators`i` and`j` in`[first, last)` such that`i` precedes`j` ,`*j < *i` is`false` .
For the second version: -
`[first, last)` is a valid range. -
`[first, last)` is ordered in ascending order according to the functors`comp` . That is, for every pair of iterators`i` and`j` in`[first, last)` such that`i` precedes`j` ,`comp(*j, *i)` is`false` .
## ComplexityThe number of comparisons is logarithmic: at most ## Exampleint main() { int A[] = { 1, 2, 3, 3, 3, 5, 8 }; const int N = sizeof(A) / sizeof(int); for (int i = 1; i <= 10; ++i) { cout << "Searching for " << i << ": " << (binary_search(A, A + N, i) ? "present" : "not present") << endl; } } The output is: Searching for 1: present Searching for 2: present Searching for 3: present Searching for 4: not present Searching for 5: present Searching for 6: not present Searching for 7: not present Searching for 8: present Searching for 9: not present Searching for 10: not present ## Notes[1] Note that you may use an ordering that is a strict weak ordering but not a total ordering; that is, there might be values [2] Note that this is not necessarily the information you are interested in! Usually, if you're testing whether an element is present in a range, you'd like to know where it is (if it's present), or where it should be inserted (if it's not present). The functions [3] This difference between RandomAccessIterator and ForwardIterator is simply because ## See also |