std::transform

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle  (C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in 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 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 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.

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

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 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.

Return value

Output iterator to the element past the last element transformed.

Complexity

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

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

Possible implementation

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; }

Notes

std::transform does not guarantee in-order application of unary_op or binary_op. To apply a function to a sequence in-order or to apply a function that modifies the elements of a sequence, use std::for_each

Example

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

Run this code

#include <string>
#include <cctype>
#include <algorithm>
#include <functional>
#include <iostream>
 
int main()
{
    std::string s("hello");
    std::transform(s.begin(), s.end(), s.begin(), std::ptr_fun<int, int>(std::toupper));
    std::cout << s;
}

Output:

HELLO

See also

for_each

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