请求转换为非标量类型

Question

在泛型编程的家庭作业中，程序未编译。我应该通过仅将代码插入指定位置而不更改任何其他内容来解决此问题。我试图通过重载运算符来使编译器理解它们对于该自定义类型的含义，但我仍然遇到相同的错误。我现在很茫然。

#include <iostream>

using namespace std;

template <typename T>
struct TripleData {
    T m_first;
    T m_second;
    T m_third;  
    T getMean() {
        return (m_first + m_second + m_third)/3;
    }

    // INSERT CODE HERE
    void operator = (const T & value) {
        m_first = m_second = m_third = value;  
    }

    void operator += (const TripleData & tridata) {
        m_first += tridata.m_first;
        m_second += tridata.m_second;
        m_third += tridata.m_third;
    }

    T & operator / (const T & divisor) {
        return m_first/divisor;
    }
    //END OF INSERTED CODE
};

template <typename T, int N>
class GenericStaticMatrix {
    T m_data[N];
public:
    T & operator()(int i) {
        return m_data[i];
    }
    int getSize() const {
        return N;
    }
    T getMean() const {
        T sum = 0;                            //Error: conversion from 'int' to non-scalar type 'TripleData<double>' requested
        for (int i=0;i<N;i++) sum+=m_data[i]; 
        T ret = sum/(double)N;                //Error: conversion from 'double' to non-scalar type 'TripleData<double>' requested
        return ret;
    }
};


int main() {

    const int size = 10;
    int i;     
    GenericStaticMatrix<TripleData<double>,size> gsm_tdd;

    for (i=0;i<size;i++) {
        gsm_tdd(i).m_first = 1.1 + i;
        gsm_tdd(i).m_second = 2.2 + i;
        gsm_tdd(i).m_third = 3.3 + i;
    }

    cout << gsm_tdd.getMean().m_first <<endl;
    cout << gsm_tdd.getMean().m_second <<endl;
    cout << gsm_tdd.getMean().m_third <<endl;

    return 0;
}

提前致谢！

Answer 1

TripleData<double> 需要运行的代码是：

T sum = 0;                // (A)
sum += m_data[i];         // (B)
T ret = sum / (double)N;  // (C)

只需从这段代码暗示的隐式接口向后工作。

// (A) implies non-explicit construction from an int
TripleData(int ); 

// (B) implies operator+=, you have this one almost right
TripleData& operator+=(const TripleData& rhs);

// (C) implies division by a **scalar** - this should NOT modify the object
TripleData operator/(double ) const;

您完全遗漏了 (A) - 您编写了一个赋值运算符，但 T x = y; 不是赋值，它是 copy-initialization。 (B) 基本上没问题，而 (C) 您使用了错误的操作数类型。我们除以 double，而不是 TripleData<double>。

请求转换为非标量类型

Conversion to non-scalar type requested

c++

templates

generic-programming