stl transform algorithm example

template < class InputIterator, class OutputIterator, class UnaryOperator >

  OutputIterator transform ( InputIterator first1, InputIterator last1,

                             OutputIterator result, UnaryOperator op );



template < class InputIterator1, class InputIterator2,

           class OutputIterator, class BinaryOperator >

  OutputIterator transform ( InputIterator1 first1, InputIterator1 last1,

                             InputIterator2 first2, OutputIterator result,

                             BinaryOperator binary_op );      

Apply function to range

The first version applies op to all the elements in the input range ([first1,last1) ) and stores each returned value in the range beginning at result .

The second version uses as argument for each call to binary_op one element from the first input range ([first1,last1) ) and one element from the second input range (beginning at first2 ).

The behavior of this function template is equivalent to:

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template < class InputIterator, class OutputIterator, class UnaryOperator > OutputIterator transform ( InputIterator first1, InputIterator last1, OutputIterator result, UnaryOperator op ) { while (first1 != last1) *result++ = op(*first1++); // or: *result++=binary_op(*first1++,*first2++); return result; }

The function allows for the destination range to be the same as one of the input ranges to make transformations in place .

Parameters

first1, last1

Input iterators to the initial and final positions of the first sequence. The range used is [first1,last1) , which contains all the elements between first1 and last1 , including the element pointed by first1 but not the element pointed by last1 .

first2

Input iterator to the initial position of the second range. The range includes as many elements as [first1,last1) .

result

Output iterator to the initial position of the range where function results are stored. The rangeincludes as many elements as [first1,last1) .

op

Unary function taking one element as argument, and returning some result value. This can either be a pointer to a function or an object whose class overloads operator() .

binary_op

Binary function taking two elements as argument (one of each of the two sequences), and returning some result value. This can either be a pointer to a function or an object whose class overloads operator() .

Return value

An iterator pointing to the element that follows the last element written in the result sequence.

Example

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// transform algorithm example #include <iostream> #include <algorithm> #include <vector> using namespace std; int op_increase (int i) { return ++i; } int op_sum (int i, int j) { return i+j; } int main () { vector<int > first; vector<int > second; vector<int >::iterator it; // set some values: for (int i=1; i<6; i++) first.push_back (i*10); // first: 10 20 30 40 50 second.resize(first.size()); // allocate space transform (first.begin(), first.end(), second.begin(), op_increase); // second: 11 21 31 41 51 transform (first.begin(), first.end(), second.begin(), first.begin(), op_sum); // first: 21 41 61 81 101 cout << "first contains:" ; for (it=first.begin(); it!=first.end(); ++it) cout << " " << *it; cout << endl; return 0; }

Output:

first contains: 21 41 61 81 101

Complexity

Linear: Performs as many assignments and applications of op or binary_op as the number of elements in the range [first1,last1) .

http://www.cplusplus.com/reference/algorithm/transform/