equal


Category: algorithms	Component type: function

Prototype

Equal is an overloaded name; there are actually two equal functions.

template <class InputIterator1
class InputIterator2>
bool equal(InputIterator1 first1
InputIterator1 last1

           InputIterator2 first2);

template <class InputIterator1
class InputIterator2

          class BinaryPredicate>
bool equal(InputIterator1 first1
InputIterator1 last1

           InputIterator2 first2
BinaryPredicate binary_pred);

Description

Equal returns true if the two ranges [first1 last1) and [first2 first2 + (last1 - first1)) are identical when compared element-by-element and otherwise returns false. [1]

The first version of equal returns true if and only if for every iterator i in [first1 last1) *i == *(first2 + (i - first1)). The second version of equal returns true if and only if for every iterator i in [first1 last1) binary_pred(*i *(first2 + (i - first1)) is true.

Definition

Defined in the standard header algorithm and in the nonstandard backward-compatibility header algo.h.

Requirements on types

For the first version:

InputIterator1 is a model of Input Iterator.
InputIterator2 is a model of Input Iterator.
InputIterator1's value type is a model of Equality Comparable.
InputIterator2's value type is a model of Equality Comparable.
InputIterator1's value type can be compared for equality with InputIterator2's value type.

For the second version:

InputIterator1 is a model of Input Iterator.
InputIterator2 is a model of Input Iterator.
BinaryPredicate is a model of Binary Predicate.
InputIterator1's value type is convertible to BinaryPredicate's first argument type.
InputIterator2's value type is convertible to BinaryPredicate's second argument type.

Preconditions

[first1 last1) is a valid range.
[first2 first2 + (last2 - last1)) is a valid range.

Complexity

Linear. At most last1 - first1 comparisons.

Example

int A1[] = { 3
1
4
1
5
9
3 };
int A2[] = { 3
1
4
2
8
5
7 };
const int N = sizeof(A1) / sizeof(int);

cout << "Result of comparison: " << equal(A1
A1 + N
A2) << endl;

Notes

[1] Note that this is very similar to the behavior of mismatch: The only real difference is that while equal will simply return false if the two ranges differ mismatch returns the first location where they do differ. The expression equal(f1 l1 f2) is precisely equivalent to the expression mismatch(f1 l1 f2).first == l1 and this is in fact how equal could be implemented.