c++ - 定义友元运算符的问题

Question

我的处理 friend > 运算符的代码有问题，但我似乎无法修复它。
我添加了 friend bool operator > (const my_int& c1, const my_int& c2); 代码，我知道它是正确的，但是在我试图实现它的主类中有点错误，不要不知道如何修复。

#include <iostream>
#include <cmath>
using namespace std;
//*********************************************************
// Function: my_int
// Purpose:  Constructor initializes the val to x
// Params:   x - the value for the val
// Calls:    none
// Uses:     none
//*********************************************************
//my_int::my_int(int x);
//*********************************************************
// Function: my_int
// Purpose:  Constructor initializes the val to 0
// Params:   none
// Calls:    none
// Uses:     none
//*********************************************************
//my_int::my_int();
//*********************************************************
// Function: my_int
// Purpose:  Constructor initializes the val to x
// Params:   x - the value for the val
// Calls:    none
// Uses:     none
//*********************************************************
//my_int::my_int();
//*********************************************************
// Function: set
// Purpose:  Sets the val to x
// Params:   x - the new value for the val
// Calls:    none
// Uses:     none
//*********************************************************
// void my_int::set(int x);
//*********************************************************************
// Function: input
// Purpose:  reads and stores a value from inp. if fin is a input
//           stream, then fin is already connected to a file.User enters
//           a value and ask the user to re-enter the data if the
//           user enters an incorrect value.
// Params:   inp -- the input stream
// Calls:    none
// Uses:     istream
//*********************************************************************
//void my_int:: input(istream& inp);
//*********************************************************************
// Function: output
// Purpose:  display the val on fout. if fout is a  output stream
//           then fout is already  connected to a file
// Params:   fout -- the output stream
// Calls:    none
// Uses:     ostream
//*********************************************************************
//void my_int::output(ostream& fout);
//*********************************************************
// Function: get_int
// Purpose:  returns the val
// Params:   none
// Calls:    none
// Uses:     none
//**********************************************************
// int my_int::get_int()
//*********************************************************
// Function: is_prime
// Purpose:  object num contains a valid positive value
//           returns true if num is prime; otherwise
//           returns false
// Params:   num  - the value to be checked for prime
// Calls:    sqrt
// Uses:     cmath
//*********************************************************
// bool is_prime(const my_int& num);

class my_int
{
public:
    my_int(int x);
    my_int();

    void set(int x);

    void input(istream& inp);

    void output(ostream& fout) const;

    int get_int() const;

    friend bool operator >(const my_int& c1, const my_int& c2);

private:
    int val;
};

bool is_prime(const my_int& num);

int main()
{
    my_int value1;

    value1.input(cin);

    value1.output(cout);

    if (is_prime(value1))
        cout << "  is a prime number  \n";
    else
        cout << " is not a prime number \n";

    return 0;
}

my_int::my_int(int x)
{
    val = x;
}

my_int::my_int()
{
    val = 0;
}

void my_int::set(int a)
{
    val = a;
}

void my_int::output(ostream& fout) const
{
    fout << " The value is equal to " << val << endl;
}

int my_int::get_int() const
{
    return val;
}

bool operator >(my_int& c1, my_int& c2)
{
    if (c1.val > c2.val)
        return (true);
    else
        return (false);

}

void my_int::input(istream& inp)
{
    cout << "Enter a positive value greater than 1  ";
    inp >> val;
    while (val <= 1)
    {
        cout << "Entered an Invalid value \n";
        cout << "Enter a positive value greater than 1 \n";
        inp >> val;
    }
}

//num has been given a value and returns true if the value is a
//prime number and false otherwise

bool is_prime(const my_int& num)
{
    double limit;
    int n;      //divisor
    bool prime= true;

    limit = sqrt(static_cast<double>(num.get_int()));

    n = 2;

    while (n <= limit && prime)
    {
        if (num.get_int() % n == 0)
        prime = false;
        else
        n++;
    }
    return prime;
}

Answer 1

你需要这样的东西:

bool operator > (my_int& c1, my_int& c2)
{
  return c1.val > c2.val;
}

然后数据成员的名字是val，他们的类型是int。在 C++ 中调用 c1.int 没有意义。和图案

if (x)
  return true;
else
  return false;

又长又单调。您可以return x;。

除此之外，您应该考虑传递 const 引用。这将允许您绑定(bind)到临时值:

bool operator > (const my_int& c1, const my_int& c2) { ... }

您需要同时修改声明和定义。