C++和标准库速成(十二)—

练习1.1

题目

修改下面的Employee结构体，将其放在一个名为HR的名称空间中。你必须对main()中的代码进行那些修改才能使用此新实现？此外，修改代码使用C++20的指派初始化器。

// employee模块接口文件
export module employee;

export struct Employee {
	char firstInitial;
	char lastInitial;
	int employeeNumber;
	int salary;
};

// main
// import <iostream>;
// import <format>;
import std.core;
import employee;

int main() {
	Employee anEmployee;
	anEmployee.firstInitial = 'J';
	anEmployee.lastInitial = 'D';
	anEmployee.employeeNumber = 42;
	anEmployee.salary = 80'000;
	std::cout << std::format("Employee: {}{}\n", anEmployee.firstInitial, anEmployee.lastinitial);
	std::cout << std::format("Number: {}\n", anEmployee.employeeNumber);
	std::cout << std::format("Salary: ${}\n", anEmployee.salary);
}

答案

// employee模块接口文件
export module employee;

namespace HR {
	export struct Employee {
		char firstInitial;
		char lastInitial;
		int employeeNumber;
		int salary;
	};
}

// main()
import std.core;
import employee;

int main() {
	HR::Employee anEmployee{
		.firstInitial = 'J',
		.lastInitial = 'D',
		.employeeNumber = 42,
		.salary = 80'000
	};

	std::cout << std::format("Employee: {}{}\n", anEmployee.firstInitial, anEmployee.lastInitial);
	std::cout << std::format("Number: {}\n", anEmployee.employeeNumber);
	std::cout << std::format("Salary: {}\n", anEmployee.salary);
}

练习1.2

题目

以练习1.1的结果为基础，并向Employee添加一个枚举数据成员title，以指定某个雇员是经理，高级工程师还是工程师。你将选用哪种枚举类型？无论需要添加什么，都将其添加到HR名称空间中。在main()函数中测试新的Employee数据成员。使用switch语句为title打印出易于理解的字符串。

答案

// employee模块接口文件
export module employee;

namespace HR {
	export enum class position {
		MANAGER,
		ENGINEER,
		SENIOR_ENGINEER
	};

	export struct Employee {
		char firstInitial;
		char lastInitial;
		int employeeNumber;
		int salary;
		position title;
	};
}

// main()
import std.core;
import employee;

int main() {
	std::string title;
	HR::Employee anEmployee{
		.firstInitial = 'J',
		.lastInitial = 'D',
		.employeeNumber = 42,
		.salary = 80'000,
		.title = HR::position::ENGINEER
	};

	std::cout << std::format("Employee: {}{}\n", anEmployee.firstInitial, anEmployee.lastInitial);
	std::cout << std::format("Number: {}\n", anEmployee.employeeNumber);
	std::cout << std::format("Salary: {}\n", anEmployee.salary);

	switch (anEmployee.title) {
	case HR::position::ENGINEER:
		title = "Engineer";
		break;
	case HR::position::MANAGER:
		title = "Manager";
		break;
	case HR::position::SENIOR_ENGINEER:
		title = "Senior Engineer";
		break;
	}

	if (!title.empty()) {
		std::cout << std::format("Title: {}\n", title);
	}
}

练习1.3

题目

使用std::array存储练习1.2中具有不同数据的3个Employee实例，然后使用基于范围的for循环打印出array中的雇员。

答案

// main()
import std.core;
import employee;

static const std::string title(HR::position pos) {
	std::string title;

	switch (pos) {
	case HR::position::ENGINEER:
		title = "Engineer";
		break;
	case HR::position::MANAGER:
		title = "Manager";
		break;
	case HR::position::SENIOR_ENGINEER:
		title = "Senior Engineer";
		break;
	}
	return title;
}

static void display(HR::Employee employee) {
	std::cout << std::format("Employee: {} {}\n", employee.firstInitial, employee.lastInitial);
	std::cout << std::format("Number: {}\n", employee.employeeNumber);
	std::cout << std::format("Salary: {}\n", employee.salary);
	std::cout << std::format("Title: {}\n\n", title(employee.title));
}

int main() {
	std::array<HR::Employee, 3> employees{ {
		{'J', 'D', 42, 80'000, HR::position::MANAGER },
		{'A', 'H', 43, 60'000, HR::position::SENIOR_ENGINEER },
		{'C', 'B', 44, 40'000, HR::position::ENGINEER }
	}};

	for (auto& employee : employees) {
		display(employee);
	}
}

练习1.4

题目

进行与练习1.3相同的操作，但使用std::vector而不是array，并使用push_back()将元素插入vector中。

答案

// main()
import std.core;
import employee;

static const std::string title(HR::position pos) {
	std::string title;

	switch (pos) {
	case HR::position::ENGINEER:
		title = "Engineer";
		break;
	case HR::position::MANAGER:
		title = "Manager";
		break;
	case HR::position::SENIOR_ENGINEER:
		title = "Senior Engineer";
		break;
	}
	return title;
}

static void display(HR::Employee employee) {
	std::cout << std::format("Employee: {} {}\n", employee.firstInitial, employee.lastInitial);
	std::cout << std::format("Number: {}\n", employee.employeeNumber);
	std::cout << std::format("Salary: {}\n", employee.salary);
	std::cout << std::format("Title: {}\n\n", title(employee.title));
}

int main() {
	HR::Employee employee1 { 'J', 'D', 42, 80'000, HR::position::MANAGER };
	HR::Employee employee2 { 'A', 'H', 43, 60'000, HR::position::SENIOR_ENGINEER };
	HR::Employee employee3 { 'C', 'B', 44, 40'000, HR::position::ENGINEER };

	std::vector<HR::Employee> employees;
	employees.push_back(employee1);
	employees.push_back(employee2);
	employees.push_back(employee3);

	for ( auto& employee : employees ) {
		display(employee);
	}
}

练习1.5

题目

修改下面的AirlineTicket类，以尽可能地使用引用，并正确使用const。

// airline_ticket模块接口文件
export module airline_ticket;

// import <string>;
import std.core; // MSVC

export class AirlineTicket {
public:
	AirlineTicket(); // constructor
	~AirlineTicket(); // destructor

	double calculatePriceInDollars();

	std::string getPassengerName();
	void setPassengerName(std::string name);

	int getNumberOfMiles();
	void setNumberOfMiles(int miles);

	bool hasEliteSuperRewardsStatus();
	void setHasEliteSuperRewardsStatus(bool status);

private:
	std::string m_passengerName;
	int m_numberOfMiles;
	bool m_hasEliteSuperRewardsStatus;
};

// airline_ticket模块实现文件
module airline_ticket;

AirlineTicket::AirlineTicket() :
	m_passengerName{ "Unknown Passenger" },
	m_numberOfMiles{ 0 },
	m_hasEliteSuperRewardsStatus{ false } {
}

AirlineTicket::~AirlineTicket() {
	// nothong to do in terms of cleanup.
}

double AirlineTicket::calculatePriceInDollars() {
	if (hasEliteSuperRewardsStatus()) {
		// elite super rewards customers fly for free!
		return 0;
	}
	// the cost of the ticket is  the number of milies times 0.1.
	// real airlines probably have a more complicated formula!
	return getNumberOfMiles() * 0.1;
}

std::string AirlineTicket::getPassengerName() {
	return m_passengerName;
}

void AirlineTicket::setPassengerName(std::string name) {
	m_passengerName = name;
}

int AirlineTicket::getNumberOfMiles() {
	return m_numberOfMiles;
}

void AirlineTicket::setNumberOfMiles(int miles) {
	m_numberOfMiles = miles;
}

bool AirlineTicket::hasEliteSuperRewardsStatus() {
	return m_hasEliteSuperRewardsStatus;
}

void AirlineTicket::setHasEliteSuperRewardsStatus(bool status) {
	m_hasEliteSuperRewardsStatus = status;
}

答案

// airline_ticket模块接口文件
export module airline_ticket;

// import <string>;
import std.core; // MSVC

export class AirlineTicket {
public:
	AirlineTicket(); // constructor
	~AirlineTicket(); // destructor

	double calculatePriceInDollars() const;

	const std::string& getPassengerName() const;
	void setPassengerName(const std::string& name);

	int getNumberOfMiles() const;
	void setNumberOfMiles(int miles);

	bool hasEliteSuperRewardsStatus() const;
	void setHasEliteSuperRewardsStatus(bool status);

private:
	std::string m_passengerName;
	int m_numberOfMiles;
	bool m_hasEliteSuperRewardsStatus;
};

// airline_ticket模块实现文件
module airline_ticket;

AirlineTicket::AirlineTicket() :
	m_passengerName{ "Unknown Passenger" },
	m_numberOfMiles{ 0 },
	m_hasEliteSuperRewardsStatus{ false } {
}

AirlineTicket::~AirlineTicket() {
	// nothong to do in terms of cleanup.
}

double AirlineTicket::calculatePriceInDollars() const {
	if (hasEliteSuperRewardsStatus()) {
		// elite super rewards customers fly for free!
		return 0;
	}
	// the cost of the ticket is  the number of milies times 0.1.
	// real airlines probably have a more complicated formula!
	return getNumberOfMiles() * 0.1;
}

const std::string& AirlineTicket::getPassengerName() const {
	return m_passengerName;
}

void AirlineTicket::setPassengerName(const std::string& name) {
	m_passengerName = name;
}

int AirlineTicket::getNumberOfMiles() const {
	return m_numberOfMiles;
}

void AirlineTicket::setNumberOfMiles(int miles) {
	m_numberOfMiles = miles;
}

bool AirlineTicket::hasEliteSuperRewardsStatus() const {
	return m_hasEliteSuperRewardsStatus;
}

void AirlineTicket::setHasEliteSuperRewardsStatus(bool status) {
	m_hasEliteSuperRewardsStatus = status;
}

练习1.6

题目

修改练习1.5中的AirlineTicket类，使其包含一个可选的常旅客号码。表示此可选数据成员的最佳方法是什么？添加一个设置器和获取器来设置和获取常旅客号码。修改main()函数以测试你的实现。

答案

// airline_ticket模块接口文件
export module airline_ticket;

// import <string>;
import std.core; // MSVC

export class AirlineTicket {
public:
	AirlineTicket(); // constructor
	~AirlineTicket(); // destructor

	double calculatePriceInDollars();

	std::string getPassengerName();
	void setPassengerName(std::string name);

	int getNumberOfMiles();
	void setNumberOfMiles(int miles);

	void setFrequentFlyerNumber(int frequentFlyerNumber);
	std::optional<int> getFrequentFlyerNumber() const;

	bool hasEliteSuperRewardsStatus();
	void setHasEliteSuperRewardsStatus(bool status);

private:
	std::string m_passengerName;
	int m_numberOfMiles;
	std::optional<int> m_frequentFlyerNumber;
	bool m_hasEliteSuperRewardsStatus;
};

// airline_ticket模块实现文件
module airline_ticket;

AirlineTicket::AirlineTicket() :
	m_passengerName{ "Unknown Passenger" },
	m_numberOfMiles{ 0 },
	m_hasEliteSuperRewardsStatus{ false } {
}

AirlineTicket::~AirlineTicket() {
	// nothong to do in terms of cleanup.
}

double AirlineTicket::calculatePriceInDollars() {
	if (hasEliteSuperRewardsStatus()) {
		// elite super rewards customers fly for free!
		return 0;
	}
	// the cost of the ticket is  the number of milies times 0.1.
	// real airlines probably have a more complicated formula!
	return getNumberOfMiles() * 0.1;
}

std::string AirlineTicket::getPassengerName() {
	return m_passengerName;
}

void AirlineTicket::setPassengerName(std::string name) {
	m_passengerName = name;
}

int AirlineTicket::getNumberOfMiles() {
	return m_numberOfMiles;
}

void AirlineTicket::setNumberOfMiles(int miles) {
	m_numberOfMiles = miles;
}

void AirlineTicket::setFrequentFlyerNumber(int frequentFlyerNumber) {
	m_frequentFlyerNumber = frequentFlyerNumber;
}
std::optional<int> AirlineTicket::getFrequentFlyerNumber() const {
	return m_frequentFlyerNumber;
}

bool AirlineTicket::hasEliteSuperRewardsStatus() {
	return m_hasEliteSuperRewardsStatus;
}

void AirlineTicket::setHasEliteSuperRewardsStatus(bool status) {
	m_hasEliteSuperRewardsStatus = status;
}

// main()
import std.core;
import airline_ticket;

int main() {
	AirlineTicket myTicket;
	myTicket.setPassengerName("Sherman T. Socketwrench");
	myTicket.setNumberOfMiles(700);
	myTicket.setFrequentFlyerNumber(123'456);
	const double cost{ myTicket.calculatePriceInDollars() };
	std::cout << std::format("This ticket will cost ${}\n", cost);

	const auto frequentFlyerNumber{ myTicket.getFrequentFlyerNumber() };
	if (frequentFlyerNumber) {
		std::cout << std::format("Frequent flyer number: {}\n", frequentFlyerNumber.value());
	}
	else {
		std::cout << "No frequent flyer number.\n";
	}
}