c++ - 范围界定错误并且不能有 cv 限定符？

Question

我的问题与 Time 项目有关，我将在下面完整发布该项目以提供背景信息。我所做的大部分都是正确的，但是当涉及到加法和减法运算符定义时，我遇到了范围界定错误的问题。编译器找不到我的私有(private)成员。 (运算符用于如果用户在小时内输入 25，它会循环回到一。)整个项目正在创建已定义方法的实例。无论如何，第二个错误与运算符(operator)本身有关。我得到一个错误

 non-member function cannot have cv-qualifier

做研究告诉我这个错误是由于改变常量而发生的，在我的例子中是时间本身。我看不出我在哪里做的。我希望我很清楚，如果需要可以澄清。 .h 文件来自练习本身，除了添加私有(private)成员外，我无法更改它。

 #ifndef TIME_H_
#define TIME_H_

#include <iostream>
#include <string>
/***  Time class**  The Time class contains time as   
hours:minutes:seconds:milliseconds (AM/PM).*/

class Time {
public:
/** *  Constructor with zero values */
Time();

/** *  Constructors with arguments */
Time(long long time);
Time(int hours, int minutes, int seconds, int milli);

/** *  Deconstructor */
virtual ~Time();

/** *  Return time as   a  long long value representing time in milliseconds */
long long asLong() const;

/** *  Provide a  string in the format hours:minutes:seconds:milliseconds. *  For example 1:45:30:56 PM */
std::string toString() const;

/** *  Output the time to   an   output stream as hours:minutes:seconds:milliseconds AM/PM */
friend std::ostream& operator <<(std::ostream&, const Time&);

// Output a Time to an output stream

/** *  Declare ordering relationships */
friend bool operator <(const Time&, const Time&);
friend bool operator >(const Time&, const Time&);
friend bool operator ==(const Time &a, const Time &b);

/** *  Declare addition and subtraction */
Time operator +(const Time&) const;
Time operator -(const Time&) const;

private:
int hours;
int minutes;
int seconds;
int millis;
};

 #endif /*   TIME_H_ */

然后是源本身。

#include "Time.h"
#include <sstream>
#include <string>

using namespace std;

// Defualt Constructor
Time::Time() {
    hours = 0;
    minutes = 0;
    seconds = 0;
    millis = 0;
}

// Constructors with arguments

Time::Time(long long timeValue) {
    long long tempValue = timeValue;
    millis = tempValue % 1000;
    tempValue /= 1000;
    seconds = tempValue % 60;
    tempValue /= 60;
    minutes = tempValue % 60;
    tempValue /= 60;
    hours = tempValue;
}

Time::Time(int hours, int minutes, int seconds, int millis) {
    this->hours = hours;
    this ->minutes = minutes;
    this -> seconds = seconds;
    this -> millis = millis;

}

// Destructor
Time::~Time() {

}

// Return time in term of milliseconds.

long long Time::asLong() const {
    long long timeValue = (long long) hours;
    timeValue = (timeValue * 60) + minutes;
    timeValue = (timeValue * 60) + seconds;
    timeValue = (timeValue * 1000) + millis;
    return timeValue;
}

// Formatting

std::string Time::toString() const {
    ostringstream  v1;
    string ph;

    if (hours <= 12)
        ph = "am";
    else
        ph = "pm";

    v1 << hours % 12 << ":" << minutes << ":" << seconds << ":" << millis << ph;

    return v1.str();
}

// Time to Output Stream
ostream& operator <<(ostream& a, const Time& b)
{
    return a << b.toString();
}

// Ordering Relationships
bool operator <(const Time&t1, const Time&t2)
{
    return t1.asLong() < t2.asLong();
}

bool operator >(const Time&t1, const Time&t2)
  {
    return t1.asLong() > t2.asLong();
 }
bool operator ==(const Time &a, const Time &b)
{
    return a.asLong() == b.asLong();
}

// Declare addition and Subtraction
Time operator +(const Time&) const
{
    int a,b,c,d;
    a = t1.hours+t2.hours;
    b = t1.minutes+t2.minutes;
    c = t1.seconds+t2.seconds;
    d = t1.millis+t2.millis;
    if (d > 999)
    {
        c = c+1;
        d = d - 1000;
    }
    if (c > 59)
    {
        b = b + 1;
        c = c - 60;
    }
    if (b > 59)
    {
        a = a+1;
        b = b-60;
    }
    if (a > 24)
    {
        a = a - 24;
    }
    return Time(a,b,c,d);
}
  Time operator -(const Time&) const
   {
       int a,b,c,d;
       a = t1.hours-t2.hours;
       b = t1.minutes-t2.minutes;
       c = t1.seconds-t2.seconds;
       d = t1.millis - t2.millis;
       if (d < 0)
       {
           c = c -1;
           d = d + 1000;
       }
       if (c < 0)
       {
           b = b - 1;
           c = c + 60;
       }
       if (b < 0)
       {
           a = a + 1;
           b = b - 60;
       }
       if (a < 24)
       {
       a = a + 24;
       }

       return Time(a,b,c,d);
   } 

Answer 1

以防万一，非成员函数是友元函数。在非成员函数中，没有this参数。他们不需要简历限定符。你为什么不改变:

friend bool operator <(const Time&, const Time&);
friend bool operator >(const Time&, const Time&);
friend bool operator ==(const Time &a, const Time &b);

到

bool operator <(const Time &a);
bool operator >(const Time &a);
bool operator ==(const Time &a);