std::equal
From Cppreference
| Defined in header <algorithm>
| ||
| template< class InputIterator1, class InputIterator2 >
bool equal( InputIterator1 first1, InputIterator1 last1, | (1) | |
| template< class InputIterator1, class InputIterator2, class BinaryPredicate >
bool equal( InputIterator1 first1, InputIterator1 last1, | (2) | |
Returns true if the elements are the same in two ranges: one defined by [first1, last1) and another starting at first2. The first version of the function uses operator== to compare the elements, the second uses the given binary predicate p.
Contents |
[edit] Parameters
| first1, last1 | - | the first range of the elements to compare | |||||||||
| first2 | - | beginning of the second range of the elements to compare | |||||||||
| p | - | binary predicate which returns true if the elements should be treated as equal. The signature of the predicate function should be equivalent to the following:
The signature does not need to have const &, but the function must not modify the objects passed to it. | |||||||||
[edit] Return value
true if the elements in the two ranges are equal
[edit] Complexity
At most last1 - first1 applications of the predicate
[edit] Equivalent function
| First version |
|---|
template<class InputIterator1, class InputIterator2> bool equal(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2) { for (; first1 != last1; ++first1, ++first2) { if (!(*first1 == *first2)) { return false; } } return true; } |
| Second version |
template<class InputIterator1, class InputIterator2, class BinaryPredicate> bool equal(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, BinaryPredicate p) { for (; first1 != last1; ++first1, ++first2) { if (!p(*first1, *first2)) { return false; } } return true; } |
[edit] Example
The following code uses equal() to compare two vectors of integers:
#include <algorithm> #include <vector> int main() { std::vector<int> v1{1, 2, 3, 4, 5}; std::vector<int> v2{1, 2, 3, 4, 5}; std::vector<int> v3{5, 4, 3, 2, 1}; if (std::equal(v1.begin(), v1.end(), v2.begin())) { std::cout << "v1 == v2\n"; } else { std::cout << "v1 != v2\n"; } if (std::equal(v1.begin(), v1.end(), v3.begin())) { std::cout << "v1 == v3\n"; } else { std::cout << "v1 != v3\n"; } }
Output:
v1 == v2 v1 != v3
| finds the first element satisfying specific criteria (function template) | ||
| returns true if one range is lexicographically less than another (function template) | ||
| finds the first position where two ranges differ (function template) | ||
| searches for a range of elements (function template) | ||
