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std::equal - cppreference.com

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Definido no cabeçalho

<algorithm>

template< class InputIt1, class InputIt2 > bool equal( InputIt1 first1, InputIt1 last1, InputIt2 first2 );

 (1)

template< class InputIt1, class InputIt2, class BinaryPredicate > bool equal( InputIt1 first1, InputIt1 last1, InputIt2 first2, BinaryPredicate p );

 (2)

Retorna true se os elementos são os mesmos em duas gamas: uma definida por [first1, last1) e outra a partir de first2. A primeira versão da função usa operator== para comparar os elementos, o segundo usa o predicado binário dado p.

Original:

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.

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Parâmetros

first1, last1 -

a primeira gama de elementos para comparar

Original:

the first range of the elements to compare

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first2 -

no início do segundo intervalo de elementos para comparar

Original:

beginning of the second range of the elements to compare

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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 InputIt1 and InputIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively.

​

Type requirements
-InputIt1, InputIt2 must meet the requirements of InputIterator.

Valor de retorno

true se os elementos dos dois intervalos são iguais

Original:

true if the elements in the two ranges are equal

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Notas

std::equal não pode ser usado para comparar os intervalos formados pelos iteradores de std::unordered_set, std::unordered_multiset, std::unordered_map, std::unordered_multimap ou porque a ordem em que os elementos são armazenados nos recipientes podem ser diferentes mesmo se os dois recipientes de armazenar os mesmos elementos.

Original:

std::equal may not be used to compare the ranges formed by the iterators from std::unordered_set, std::unordered_multiset, std::unordered_map, or std::unordered_multimap because the order in which the elements are stored in those containers may be different even if the two containers store the same elements.

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{{{1}}}

Original:

{{{2}}}

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Complexidade

No máximo last1 - first1 aplicações do predicado

Original:

At most last1 - first1 applications of the predicate

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Possível implementação

First version 
template<class InputIt1, class InputIt2>
bool equal(InputIt1 first1, InputIt1 last1, 
           InputIt2 first2)
{
    for (; first1 != last1; ++first1, ++first2) {
        if (!(*first1 == *first2)) {
            return false;
        }
    }
    return true;
}
Second version 
template<class InputIt1, class InputIt2, class BinaryPredicate>
bool equal(InputIt1 first1, InputIt1 last1, 
           InputIt2 first2, BinaryPredicate p)
{
    for (; first1 != last1; ++first1, ++first2) {
        if (!p(*first1, *first2)) {
            return false;
        }
    }
    return true;
}

Exemplo

O código a seguir usa equal() para testar se uma string é um palíndromo

Original:

The following code uses equal() to test if a string is a palindrome

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#include <iostream>
#include <algorithm>
#include <string>

void test(const std::string& s)
{
    if(std::equal(s.begin(), s.begin() + s.size()/2, s.rbegin())) {
        std::cout << "\"" << s << "\" is a palindrome\n";
    } else {
        std::cout << "\"" << s << "\" is not palindrome\n";
    }
}
int main()
{
    test("radar");
    test("hello");
}

Saída: 

"radar" is a palindrome
"hello" is not palindrome

encontra o primeiro elemento satisfazer critérios específicos

Original:

finds the first element satisfying specific criteria

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(modelo de função) [edit]

retorna true se um intervalo é lexicograficamente menor do que outro

Original:

returns true if one range is lexicographically less than another

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(modelo de função) [edit]

encontra a primeira posição em que dois intervalos diferentes

Original:

finds the first position where two ranges differ

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(modelo de função) [edit]
searches for a range of elements
(modelo de função) [edit]