std::equal

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Defined in header <algorithm>

template< class InputIterator1, class InputIterator2 >

bool equal( InputIterator1 first1, InputIterator1 last1,

            InputIterator2 first2 );
(1)
template< class InputIterator1, class InputIterator2, class BinaryPredicate >

bool equal( InputIterator1 first1, InputIterator1 last1,

            InputIterator2 first2, BinaryPredicate p );
(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:

bool pred(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The types Type1 and Type2 must be such that objects of types InputIterator1 and InputIterator2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively.

[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

[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
find
find_if
find_if_not


(C++11)
finds the first element satisfying specific criteria
(function template)
lexicographical_compare
returns true if one range is lexicographically less than another
(function template)
mismatch
finds the first position where two ranges differ
(function template)
search
searches for a range of elements
(function template)