transform知识点小结

一、来源与功能

来自<algorithm>头文件，对序列进行变换操作

二、使用方式

• unary operation(1)

template <class InputIterator, class OutputIterator, class UnaryOperation>
  OutputIterator transform (InputIterator first1, InputIterator last1,
                            OutputIterator result, UnaryOperation op);

• binary operation(2)

template <class InputIterator1, class InputIterator2,
          class OutputIterator, class BinaryOperation>
  OutputIterator transform (InputIterator1 first1, InputIterator1 last1,
                            InputIterator2 first2, OutputIterator result,
                            BinaryOperation binary_op);

三、参数解释

• first1, last1:第一个序列的元素范围[first1,last1)
• first2:第二个序列的元素范围[first2, first2+last1-first1)
• op:一元操作符
• binary_op：二元操作符，可以是函数指针或函数对象

四、返回值

指向结果序列最后一个元素的下一个位置

五、示例程式

#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

namespace sxg00 {
    void printSeq(vector<int>& vec) {
        for (int i = 0; i < vec.size(); i++) {
            cout << vec[i] << " ";
        }
        cout << '\n';
    }

    int op_increase(int i) {
        return ++i;
    }
    void test_transform() {
        vector<int> source;

         for (int i=1; i<6; i++)
            source.push_back (i*10);  

        vector<int> des;
        des.resize(source.size());

        // test transform Unary operation

        /**
         unary operation(1) 
        template <class InputIterator, class OutputIterator, class UnaryOperation>
            OutputIterator transform (InputIterator first1, InputIterator last1,
                                  OutputIterator result, UnaryOperation op);
         */
        vector<int>::iterator it = transform(source.begin(), source.end(), des.begin(), op_increase);
        cout << *(--it) << endl;
        cout << "des contains:";
        printSeq(des);



        // test transform Binary operation
        /**
         binary operation(2)    
    template <class InputIterator1, class InputIterator2,
          class OutputIterator, class BinaryOperation>
                OutputIterator transform (InputIterator1 first1, InputIterator1 last1,
                                          InputIterator2 first2, OutputIterator result,
                                          BinaryOperation binary_op);
         */
        transform(source.begin(), source.end(), des.begin(), source.begin(), std::plus<int>());
        cout << "source contains:";
        printSeq(source);
    }
}

int main() {
    sxg00::test_transform();
    return 0;
}

输出结果

51
des contains:11 21 31 41 51
source contains:21 41 61 81 101

参考链接

http://www.cplusplus.com/reference/algorithm/transform/?kw=transform