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Standard Template Library Programmer's Guide
(document number: 007-3426-004 / published: 1999-05-21) table of contents | additional info | download
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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.