std::transform - cppreference.com

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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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Parametri

first1, last1	-	la prima gamma di elementi per trasformare Original: the first range of elements to transform The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
first2	-	all'inizio del secondo intervallo di elementi da trasformare Original: the beginning of the second range of elements to transform 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, può essere uguale o `first1` `first2` Original: the beginning of the destination range, may be equal to `first1` or `first2` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
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`.

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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Complessità

esattamente std::distance(first1, last1) applicazioni di unary_op

Original:

exactly std::distance(first1, last1) applications of unary_op

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esattamente std::distance(first1, last1) applicazioni di binary_op

Original:

exactly std::distance(first1, last1) applications of binary_op

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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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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; }

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;
}

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:

Vedi anche


	applica una funzione ad una serie di elementi Original: applies a function to a range of elements 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]