stl transform algorithm example

最新推荐文章于 2023-05-17 11:24:11 发布

君记否

最新推荐文章于 2023-05-17 11:24:11 发布

阅读量852

点赞数

分类专栏： stl 文章标签： algorithm iterator class function returning input

stl 专栏收录该内容

13 篇文章

订阅专栏

本文详细介绍了 C++ 标准库中的 transform 函数用法，包括单输入单输出及双输入单输出两种模板形式。提供了具体的代码示例，展示了如何使用自定义函数对容器内的元素进行操作。

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:

1 2 3 4 5 6 7 8

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) .

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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

// 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;

}