C++ std::multiplies实现无视类型执行乘法

怼烎@ 2022-10-05 14:52 78阅读 0赞

`std::multiplies`是乘法的二元函数对象。

常被用于`std::transform`或者`std::accumulate`等的运算算子。  
**例子一.实现两个数组元素的相乘**

// C++ program to illustrate std::multiplies 
    // by multiplying the respective elements of 2 arrays 
    #include <iostream> // std::cout 
    #include <functional> // std::multiplies 
    #include <algorithm> // std::transform 
      
    int main() 
    { 
        // First array 
        int first[] = { 1, 2, 3, 4, 5 }; 
      
        // Second array 
        int second[] = { 10, 20, 30, 40, 50 }; 
      
        // Result array 
        int results[5]; 
      
        // std::transform applies std::multiplies to the whole array 
        std::transform(first, first + 5, second, results, std::multiplies<int>()); 
      
        // Printing the result array 
        for (int i = 0; i < 5; i++) 
            std::cout << results[i] << " "; 
      
        return 0; 
    }
    
    //output:10 40 90 160 250

**例子二.实现多个数字的累乘**

#include <bits/stdc++.h> 
      
    int main() 
    { 
        // Array with elements to be multiplying 
        int arr[] = { 10, 20, 30 }; 
      
        // size of array 
        int size = sizeof(arr) / sizeof(arr[0]); 
      
        // Variable with which array is to be multiplied 
        int num = 10; 
      
        // Variable to store result 
        int result; 
      
        // using std::accumulate to perform multiplication on array with num 
        // using std::multiplies 
        result = std::accumulate(arr, arr + size, num, std::multiplies<int>()); 
      
        // Printing the result 
        std::cout << "The result of 10 * 10 * 20 * 30 is " << result; 
      
        return 0; 
    }
    //output:The result of 10 * 10 * 20 * 30 is 60000

**例子三.两个vector数组元素相乘**

#include <iostream>
    #include <vector>
    #include <algorithm>
    #include <functional>
    
    int main()
    {
        std::vector<int> v1 = {10, 20, 30, 40, 50};
        std::vector<int> v2 = { 1, 2, 3, 4, 5 };
    
        std::vector<int> result(5);
        std::transform(v1.begin(), v1.end(), v2.begin(), result.begin(), std::multiplies<int>());
    
        for (int i : result) {
            std::cout << i << "\t";
        }
        std::cout << std::endl;
    
        return 0;
    }