std::transform
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<td><algorithm>
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<td >OutputIt transform( InputIt first1, InputIt last1, OutputIt d_first,
<td > (1) </td> <td class="tdclnopad"> </td> </tr> <tr class="tdcl ">
<td >OutputIt transform( InputIt1 first1, InputIt1 last1, InputIt2 first2,
<td > (2) </td> <td class="tdclnopad"> </td> </tr> Template:ddcl list end
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
.
Contents 
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 &. 
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 &. 
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
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 outoforder implementations of std::transform. To apply a function to a sequence inorder, use std::for_each.
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; } 
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