std::transform

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Defined in header `<algorithm>`

template< class InputIterator, class OutputIterator, class UnaryOperation > OutputIterator transform( InputIterator first1, InputIterator1 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.

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] Equivalent function

First version

template<class InputIterator, class OutputIterator, class UnaryOperation>
OutputIterator copy(InputIterator first1, 
                    InputIterator last1,
                    OutputIterator d_first, 
                    UnaryOperation unary_op)
{
    while (first1 != last1) {
        *d_first++ = unary_op(*first1++);
    }
    return d_first;
}

Second version

template<class InputIterator1, class InputIterator2, 
         class OutputIterator, class BinaryOperation>
OutputIterator copy(InputIterator first1, 
                    InputIterator last1,
                    InputIterator first2, 
                    OutputIterator d_first, 
                    BinaryOperation binary_op)
{
    while (first1 != last1) {
        *d_first++ = binary_op(*first1++, *first2++);
    }
    return d_first;
}

[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

for_each

applies a function to a range of elements
(function template)