std::copy, std::copy_if - cppreference.com

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Elemento definito nell'header `<algorithm>`

`template< class InputIt, class OutputIt > OutputIt copy( InputIt first, InputIt last, OutputIt d_first );`	(1)

`template< class InputIt, class OutputIt, class UnaryPredicate > OutputIt copy_if( InputIt first, InputIt last, OutputIt d_first, UnaryPredicate pred );`	(2)	(dal C++11)

Copia gli elementi della gamma, definiti da [first, last), a un altro inizio gamma a d_first. La seconda funzione copia solo gli elementi per i quali il predicato pred ritorna true.

Original:

Copies the elements in the range, defined by [first, last), to another range beginning at d_first. The second function only copies the elements for which the predicate pred returns true.

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Parametri

first, last	-	dell'intervallo di elementi da copiare Original: the range of elements to copy The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
d_first	-	l'inizio del campo di destinazione. Se `d_first` è all'interno `[first, last)`, std::copy_backward deve essere usato al posto di std::copy . Original: the beginning of the destination range. If `d_first` is within `[first, last)`, std::copy_backward must be used instead of std::copy. The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
pred	-	unary predicate which returns `true` per gli elementi richiesti Original: for the required elements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. . The signature of the predicate function should be equivalent to the following: `bool pred(const Type &a);` The signature does not need to have `const &`, but the function must not modify the objects passed to it. The type `Type` must be such that an object of type `InputIt` can be dereferenced and then implicitly converted to `Type`.
Type requirements
-`InputIt` must meet the requirements of `InputIterator`.
-`OutputIt` must meet the requirements of `OutputIterator`.

Valore di ritorno

Iteratore di uscita per l'elemento nel campo di destinazione, un passato l'ultimo elemento copiato.

Original:

Output iterator to the element in the destination range, one past the last element copied.

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Complessità

Esattamente last - first assegnazioni

Original:

Exactly last - first assignments

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Esattamente last - first applicazioni del predicato

Original:

Exactly last - first applications of the predicate

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Note

In pratica, le implementazioni di std::copy evitare assegnazioni multiple e l'uso di copia di massa funzioni come std::memcpy se il tipo di valore è TriviallyCopyable

Original:

In practice, implementations of std::copy avoid multiple assignments and use bulk copy functions such as std::memcpy if the value type is TriviallyCopyable

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Possibile implementazione

First version
template<class InputIt, class OutputIt> OutputIt copy(InputIt first, InputIt last, OutputIt d_first) { while (first != last) { d_first++ = first++; } return d_first; }
Second version
template<class InputIt, class OutputIt, class UnaryPredicate> OutputIt copy_if(InputIt first, InputIt last, OutputIt d_first, UnaryPredicate pred) { while (first != last) { if(pred(first)) d_first++ = *first; first++; } return d_first; }

First version

template<class InputIt, class OutputIt>
OutputIt copy(InputIt first, InputIt last, 
              OutputIt d_first)
{
    while (first != last) {
        *d_first++ = *first++;
    }
    return d_first;
}

Second version

template<class InputIt, class OutputIt, class UnaryPredicate>
OutputIt copy_if(InputIt first, InputIt last, 
                 OutputIt d_first, UnaryPredicate pred)
{
    while (first != last) {
        if(pred(*first))
            *d_first++ = *first;
         first++;
    }
    return d_first;
}

Esempio

Il codice seguente utilizza copia sia a copiare il contenuto di un vettore ad un altro e per visualizzare il vettore risultante:

Original:

The following code uses copy to both copy the contents of one vector to another and to display the resulting vector:

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#include <algorithm>
#include <iostream>
#include <vector>
#include <iterator>
 
int main()
{
    std::vector<int> from_vector;
    for (int i = 0; i < 10; i++) {
        from_vector.push_back(i);
    }
 
    std::vector<int> to_vector(10);
 
    std::copy(from_vector.begin(), from_vector.end(), to_vector.begin());
 
    std::cout << "to_vector contains: ";
    std::copy(to_vector.begin(), to_vector.end(), 
              std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;
}

Output:

to_vector contains: 0 1 2 3 4 5 6 7 8 9

Vedi anche


	una serie di elementi in ordine inverso Original: copies a range of elements in backwards order The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]

	copia un intervallo di elementi omettendo quelli che soddisfano criteri specifici Original: copies a range of elements omitting those that satisfy specific criteria The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]