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std::transform

From cppreference.com
 
 
 
Defined in header <algorithm>
template< class InputIterator, class OutputIterator, class UnaryOperation >

OutputIterator transform( InputIterator first1,
                          InputIterator last1,
                          OutputIterator d_first,

                          UnaryOperation unary_op );
(1)
template< class InputIterator1, class InputIterator2, class OutputIterator, class BinaryOperation >

OutputIterator transform( InputIterator1 first1,
                          InputIterator1 last1,
                          InputIterator2 first2,
                          OutputIterator d_first,

                          BinaryOperation binary_op );
(2)

Applies the given function to a range and stores the result in another range, beginning at d_first. In the first version unary operation unary_op is applied to the range, defined by [first1, last1). In the second version binary operation binary_op is applied to pairs of elements from two ranges: one defined by [first1, last1) and other beginning at first2.

Contents

[edit] Parameters

first1, last1 - the first range of elements to transform
first2 - the beginning of the second range of elements to transform
d_first - the beginning of the destination range, may be equal to first1 or first2
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 InputIterator can be dereferenced and then implicitly converted to  Type. The type  Ret must be such that an object of type OutputIterator 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 InputIterator1 and InputIterator2 can be dereferenced and then implicitly converted to  Type1 and  Type2 respectively. The type  Ret must be such that an object of type OutputIterator can be dereferenced and assigned a value of type  Ret. ​

[edit] Return value

output iterator to the element past the last element transformed.

[edit] Complexity

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

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

[edit] Requirements

unary_op and binary_op have no side effects. (until C++11)

unary_op and binary_op do not invalidate any iterators, including the end iterators, or modify any elements of the ranges involved. (since C++11)

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.

[edit] Possible implementation

[edit] Example

The following code uses transform to convert a string to uppercase using the toupper function:

#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

[edit] See also

applies a function to a range of elements
(function template) [edit]