std::transform
Defined in header <algorithm>
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template< class InputIterator, class OutputIterator, class UnaryOperation > OutputIterator transform( InputIterator first1, |
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template< class InputIterator1, class InputIterator2, class OutputIterator, class BinaryOperation > OutputIterator transform( InputIterator1 first1, |
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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.
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[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:
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:
The signature does not need to have const &. |
[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
First version |
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template<class InputIterator, class OutputIterator, class UnaryOperation> OutputIterator transform(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 transform(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
applies a function to a range of elements (function template) |