C++级联函数调用

级联函数调用就是类似于下面这种调用函数的方式：

t.setHour(18).setMinute(30).setSecond(22);

它可以把原来需要三行的语句压缩到一行，而且很具有可读性

要实现这样的调用，就必须在类的成员函数之中，返回一个*this指针，这也是实现级联函数调用的关键。

所以，代码实现就像下面这样子：

Time.h

#pragma once
class Time
{
public:
	explicit Time(int h = 0, int m = 0, int s = 0);

	//set functions(the Time& return types enable cascading)
	Time& setTime(int h, int m, int s);
	Time& setHour(int h);
	Time& setMinute(int m);
	Time& setSecond(int s);

	//get functions
	unsigned int getHour()const;
	unsigned int getMinute() const;
	unsigned int getSecond() const;

	void printUniversal() const;
	void printStandard() const;
private:
	unsigned int hour, minute, second;
};

Time.cpp

#include "Time.h"
#include<iostream>
#include<stdexcept>
#include<iomanip>
using namespace std;

Time::Time(int h, int m, int s)
{
	setTime(h, m, s);
}

Time& Time::setTime(int h, int m, int s)
{
	setHour(h);
	setMinute(m);
	setSecond(s);
	return *this;
}

Time& Time::setHour(int h)
{
	if (h >= 0 && h < 24)
		hour = h;
	else throw invalid_argument("hour must be 0-23");

	return *this;//enable cascading
}
Time& Time::setMinute(int m)
{
	if (m >= 0 && m < 60)
		minute = m;
	else throw invalid_argument("minute must be 0-59");

	return *this;//enable cascading
}

Time& Time::setSecond(int s)
{
	if (s >= 0 && s < 60)
		second = s;
	else throw invalid_argument("second must be 0-59");

	return *this;//enable cascading
}

unsigned int Time::getHour() const
{
	return this->hour;
}

unsigned int Time::getMinute() const
{
	return this->minute;
}

unsigned int Time::getSecond() const
{
	return this->second;
}

//print universal-time format (HH:MM:SS)
void Time::printUniversal() const
{
	cout << setfill('0') << setw(2) << this->hour << ":" << setw(2) << this->minute << ":" << setw(2) << this->second;
}

//print standard-time format (HH:MM:SS AM or PM)
void Time::printStandard() const
{
	cout << ((hour == 0 || hour == 12) ? 12 : hour % 12) << ":" << setfill('0') << setw(2) << minute << ":" 
		<< setw(2) << second << setw(2) << ((hour < 12) ? " AM" : " PM");
}

main.cpp

#include<iostream>
#include"Time.h"
using namespace std;

int main()
{
	Time t;
	
	//级联函数调用
	t.setHour(18).setMinute(30).setSecond(22);

	cout << "Universal time: ";
	t.printUniversal();

	cout << "\nStandard time: ";
	t.printStandard();

	cout << "\n\nNew standard time: ";
	t.setTime(20, 20, 20).printStandard();

}

最终程序输出结果：

Universal time: 18:30:22
Standard time: 6:30:22 PM

New standard time: 8:20:20 PM

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