Namespace
Varianti

std::transform

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< cpp‎ | algorithm

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C++
 
Algoritmo libreria
Funzioni
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Functions
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Non modifica le operazioni di sequenza
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Non-modifying sequence operations
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Modifica delle operazioni di sequenza
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Modifying sequence operations
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Partizionamento operazioni
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Partitioning operations
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Ordinamento delle operazioni (su intervalli ordinati)
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Sorting operations (on sorted ranges)
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Binarie (le operazioni di ricerca sui campi ordinati)
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Binary search operations (on sorted ranges)
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Impostare le operazioni (su intervalli ordinati)
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Set operations (on sorted ranges)
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Heap operazioni
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Heap operations
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Minimo / massimo le operazioni
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Minimum/maximum operations
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Operazioni numeriche
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Numeric operations
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Libreria C
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C library
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Elemento definito nell'header <algorithm>
template< class InputIt, class OutputIt, class UnaryOperation >

OutputIt transform( InputIt first1, InputIt last1, OutputIt d_first,

                    UnaryOperation unary_op );
 (1)
template< class InputIt1, class InputIt2, class OutputIt, class BinaryOperation >

OutputIt transform( InputIt1 first1, InputIt1 last1, InputIt2 first2,

                    OutputIt d_first, BinaryOperation binary_op );
 (2)
std::transform applica la funzione specificata a una vasta e memorizza il risultato in un altro campo, con inizio alle d_first.
Original:
std::transform applies the given function to a range and stores the result in another range, beginning at d_first.
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Nella prima versione unary_op operazione unaria viene applicato alla serie definita da [first1, last1). Nella seconda versione del binary_op operazione binaria viene applicata a coppie di elementi da due intervalli: uno definito dal [first1, last1) e l'altro a inizio first2.
Original:
In the first version unary operation unary_op is applied to the range defined by [first1, last1). In the second version the binary operation binary_op is applied to pairs of elements from two ranges: one defined by [first1, last1) and the other beginning at first2.
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Indice

[modifica] Parametri

first1, last1 -
la prima gamma di elementi per trasformare
Original:
the first range of elements to transform
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first2 -
all'inizio del secondo intervallo di elementi da trasformare
Original:
the beginning of the second range of elements to transform
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d_first -
l'inizio del campo di destinazione, può essere uguale o first1 first2
Original:
the beginning of the destination range, may be equal to first1 or first2
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unary_op - unary operation function object that will be applied.

The signature of the function should be equivalent to the following:

 Ret fun(const Type &a);

The signature does not need to have const &.
The type  Type must be such that an object of type InputIt can be dereferenced and then implicitly converted to  Type. The type  Ret must be such that an object of type OutputIt can be dereferenced and assigned a value of type  Ret. ​

binary_op - binary operation function object that will be applied.

The signature of the function should be equivalent to the following:

 Ret fun(const Type1 &a, const Type2 &b);

The signature does not need to have const &.
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. The type  Ret must be such that an object of type OutputIt can be dereferenced and assigned a value of type  Ret. ​

Type requirements
-
InputIt must meet the requirements of InputIterator.
-
InputIt1 must meet the requirements of InputIterator.
-
InputIt2 must meet the requirements of InputIterator.
-
OutputIt must meet the requirements of OutputIterator.

[modifica] Valore di ritorno

iteratore uscita all'elemento passato l'ultimo elemento trasformato.
Original:
output iterator to the element past the last element transformed.
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[modifica] Complessità

1)
esattamente std::distance(first1, last1) applicazioni di unary_op
Original:
exactly std::distance(first1, last1) applications of unary_op
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2)
esattamente std::distance(first1, last1) applicazioni di binary_op
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exactly std::distance(first1, last1) applications of binary_op
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[modifica] Requisiti

unary_op binary_op e non hanno effetti collaterali. (fino al c++11)
Original:
unary_op and binary_op have no side effects. (fino al c++11)
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unary_op e binary_op non invalidare le iteratori, inclusi gli iteratori finali, o modificare tutti gli elementi delle catene coinvolte. (dal C++11)
Original:
unary_op and binary_op do not invalidate any iterators, including the end iterators, or modify any elements of the ranges involved. (dal C++11)
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L'intento di questi requisiti è quello di consentire implementazioni parallele o out-of-order di std::transform. Per applicare una funzione a una sequenza in ordine, utilizzare std::for_each.
Original:
The intent of these requirements is to allow parallel or out-of-order implementations of std::transform. To apply a function to a sequence in-order, use std::for_each.
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[modifica] Possibile implementazione

First version 
template<class InputIt, class OutputIt, class UnaryOperation>
OutputIt transform(InputIt first1, InputIt last1, OutputIt d_first, 
                   UnaryOperation unary_op)
{
    while (first1 != last1) {
        *d_first++ = unary_op(*first1++);
    }
    return d_first;
}
Second version 
template<class InputIt1, class InputIt2, 
         class OutputIt, class BinaryOperation>
OutputIt transform(InputIt first1, InputIt last1, InputIt first2, 
                   OutputIt d_first, BinaryOperation binary_op)
{
    while (first1 != last1) {
        *d_first++ = binary_op(*first1++, *first2++);
    }
    return d_first;
}

[modifica] Esempio

Il codice seguente utilizza trasformazione per convertire una stringa in lettere maiuscole utilizzando la funzione toupper:
Original:
The following code uses transform to convert a string to uppercase using the toupper function:
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#include <string>
#include <cctype>
#include <algorithm>
#include <iostream>
 
int main()
{
    std::string s("hello");
    std::transform(s.begin(), s.end(), s.begin(), (int (*)(int))std::toupper);
    std::cout << s;
 }

Output: 

HELLO

[modifica] Vedi anche
applica una funzione ad una serie di elementi
Original:
applies a function to a range of elements
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(funzione di modello) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/algorithm/transform&oldid=24998"