实验2
实验2
实验结论:
实验任务1:
源码:
T.h
#pragma once
#include <string>
class T
{
public:
T(int x = 0, int y = 0);
T(const T &t);
T(T &&t);
~T();
static const std::string doc;
static const int max_cnt;
void adjust(int ratio);
void display() const;
static int get_cnt();
private:
int m1, m2;
static int cnt;
friend void func();
};
void func();
T.cpp
#include "T.h"
#include <iostream>
#include <string>
const std::string T::doc{"a simple class sample"};
const int T::max_cnt = 999;
int T::cnt = 0;
T::T(int x, int y) : m1{x}, m2{y}
{
cnt++;
std::cout << "T constructor called.\n";
}
T::T(const T &t) : m1{t.m1}, m2{t.m2}
{
cnt++;
std::cout << "T copy constructor called.\n";
}
T::T(T &&t) : m1{t.m1}, m2{t.m2}
{
cnt++;
std::cout << "T move constructor called.\n";
}
T::~T()
{
cnt--;
std::cout << "T destructor called.\n";
}
void T::adjust(int ratio)
{
m1 *= ratio;
m2 *= ratio;
}
void T::display() const
{
std::cout << "(" << m1 << ", " << m2 << ")";
}
int T::get_cnt()
{
return cnt;
}
void func()
{
T t5(42);
t5.m2 = 2049;
std::cout << "t5 = "; t5.display(); std::cout << '\n';
}
task1.cpp
#include "T.h"
#include <iostream>
using namespace std;
void test_T()
{
cout << "T info: " << T::doc << endl;
cout << "T objects'max count: " << T::max_cnt << endl;
cout << "T objects'current count: " << T::get_cnt() << endl
<< endl;
T t1;
cout << "t1 = "; t1.display(); cout << endl;
T t2(3, 4);
cout << "t2 = "; t2.display(); cout << endl;
T t3(t2);
t3.adjust(2);
cout << "t3 = "; t3.display(); cout << endl;
T t4(std::move(t2));
cout << "t4 = "; t4.display(); cout << endl;
cout << "test: T objects'current count: " << T::get_cnt() << endl;
}
int main()
{
std::cout << "test Class T: \n";
test_T();
std::cout << "\ntest friend func: \n";
func();
}
运行测试截图:
回答问题:
问题1:
T.h中，在类T内部，已声明 func 是T的友元函数。在类外部，去掉line36，重新编译，程序能否正常运行。 如果能，回答YES；如果不能，以截图形式提供编译报错信息，说明原因。
原因:
如果代码其他地方调用了 func()，编译器在编译阶段找不到 func() 的声明，就会报错,函数声明告诉编译器某个函数的存在和签名（返回类型、参数等）。如果没有声明，编译器无法识别你在其他地方调用的 func()，就会报错。
问题2:
T.h中，line9-12给出了各种构造函数、析构函数。总结它们各自的功能、调用时机。
这些函数是 C++ 中类 T 的特殊成员函数，分别用于对象的创建、复制、移动和销毁。
-
构造函数
-
功能：用给定的参数初始化对象成员（如
m1和m2），如果没有提供参数，则使用默认值 0。 -
调用时机：当你创建一个新对象时，例如
T a;或T b(1, 2);。
-
-
拷贝构造函数
-
功能：用已有对象
t的内容初始化新对象，实现对象的“复制”。 -
调用时机：当你用已有对象初始化新对象时，例如
T b = a;，或者将对象作为值传递给函数时。
-
-
移动构造函数
-
功能：用右值对象
t初始化新对象，通常用于优化临时对象的转移，避免不必要的深拷贝。 -
调用时机：当你用临时对象或
std::move语义初始化新对象时，例如T c = std::move(a);。
-
-
析构函数
~T()-
功能：在对象生命周期结束时自动调用，负责清理资源（如释放内存、关闭文件等）。
-
调用时机：对象离开作用域、被显式删除（如
delete），或程序结束时。
-
问题3:
T.cpp中，line13-15，剪切到T.h的末尾，重新编译，程序能否正确编译。 如不能，以截图形式给出报错信息，分析原因。
原因:
在多个源文件（T.cpp 和 task1.cpp）中重复定义了同一个类的静态成员变量（如 T::doc、T::max_cnt、T::cnt），导致链接器（ld.exe）报“multiple definition”（多重定义）错误。在 C++ 中，静态成员变量必须在类外进行一次定义（分配内存），通常放在某个 .cpp 文件里。而在头文件 T.h 里，只能声明，不能定义（不能赋初值）。
实验任务2:
源码:
Complex.h
#include <string>
class Complex
{
public:
static const std::string doc;
Complex(double real = 0, double imag = 0);
Complex(const Complex &other);
double get_real() const;
double get_imag() const;
void add(Complex c);
friend void output(Complex c);
friend double abs(Complex c);
friend Complex add(Complex c1, Complex c2);
friend bool is_equal(Complex c1, Complex c2);
friend bool is_not_equal(Complex c1, Complex c2);
private:
double real, imag;
};
Complex.cpp
#include "Complex.h"
#include <iostream>
#include <string>
#include <math.h>
const std::string Complex::doc = "a simplified complex class";
Complex::Complex(double real, double imag)
{
this->real = real;
this->imag = imag;
}
Complex::Complex(const Complex &other)
{
this->real = other.real;
this->imag = other.imag;
}
double Complex::get_real() const
{
return this->real;
}
double Complex::get_imag() const
{
return this->imag;
}
void Complex::add(Complex c)
{
this->real += c.real;
this->imag += c.imag;
}
void output(Complex c)
{
int r = (int)c.real;
int i = (int)c.imag;
if (i >= 0)
{
printf("%d + %di", r, i);
}
else
{
printf("%d - %di", r, -i);
}
}
double abs(Complex c)
{
return sqrt(c.real * c.real + c.imag * c.imag);
}
Complex add(Complex c1, Complex c2)
{
return Complex(c1.real + c2.real, c1.imag + c2.imag);
}
bool is_equal(Complex c1, Complex c2)
{
return c1.real == c2.real && c1.imag == c2.imag;
}
bool is_not_equal(Complex c1, Complex c2)
{
return c1.real != c2.real || c1.imag != c2.imag;
}
task2.cpp
#include "Complex.h"
#include <iostream>
#include <iomanip>
#include <complex>
void test_Complex();
void test_std_complex();
int main()
{
std::cout << "*******测试1: 自定义类Complex*******\n";
test_Complex();
std::cout << "\n*******测试2: 标准库模板类complex*******\n";
test_std_complex();
}
void test_Complex()
{
using std::boolalpha;
using std::cout;
using std::endl;
cout << "类成员测试: " << endl;
cout << Complex::doc << endl << endl;
cout << "Complex对象测试: " << endl;
Complex c1;
Complex c2(3, -4);
Complex c3(c2);
Complex c4 = c2;
const Complex c5(3.5);
cout << "c1 = "; output(c1); cout << endl;
cout << "c2 = "; output(c2); cout << endl;
cout << "c3 = "; output(c3); cout << endl;
cout << "c4 = "; output(c4); cout << endl;
cout << "c5.real = " << c5.get_real()
<< ", c5.imag = " << c5.get_imag() << endl << endl;
cout << "复数运算测试: " << endl;
cout << "abs(c2) = " << abs(c2) << endl;
c1.add(c2); cout << "c1 += c2, c1 = "; output(c1); cout << endl; cout << boolalpha;
cout << "c1 == c2 : " << is_equal(c1, c2) << endl;
cout << "c1 != c2 : " << is_not_equal(c1, c2) << endl;
c4 = add(c2, c3);
cout << "c4 = c2 + c3, c4 = "; output(c4); cout << endl;
}
void test_std_complex()
{
using std::boolalpha;
using std::cout;
using std::endl;
cout << "std::complex<double>对象测试: " << endl;
std::complex<double> c1;
std::complex<double> c2(3, -4);
std::complex<double> c3(c2);
std::complex<double> c4 = c2;
const std::complex<double> c5(3.5);
cout << "c1 = " << c1 << endl;
cout << "c2 = " << c2 << endl;
cout << "c3 = " << c3 << endl;
cout << "c4 = " << c4 << endl;
cout << "c5.real = " << c5.real()
<< ", c5.imag = " << c5.imag() << endl
<< endl;
cout << "复数运算测试: " << endl;
cout << "abs(c2) = " << abs(c2) << endl;
c1 += c2;
cout << "c1 += c2, c1 = " << c1 << endl;
cout << boolalpha;
cout << "c1 == c2 : " << (c1 == c2) << endl;
cout << "c1 != c2 : " << (c1 != c2) << endl;
c4 = c2 + c3;
cout << "c4 = c2 + c3, c4 = " << c4 << endl;
}
运行测试截图:
回答问题:
问题1:
比较自定义类Complex和标准库模板类complex的用法，在使用形式上，哪一种更简洁？函数和运算内在有关联吗？
- 标准库模板类
std::complex用法更简洁。
因为它直接支持各种运算符（如+、-、*、/），并且相关函数（如abs、real、imag）都是标准库接口，无需额外声明或友元设置，直接调用即可。而自定义类Complex通常需要自己实现运算符重载和相关函数，代码更繁琐。 - 函数和运算有内在关联。
运算符重载和相关函数（如abs）都需要访问复数的实部和虚部，因此它们实现时往往需要访问类的成员数据。
问题2:
2-1：自定义Complex中, output/abs/add/ 等均设为友元，它们真的需要访问私有数据吗？（回答“是/否”并 给出理由）
是。
理由：这些函数如果不是类成员函数，而是独立的普通函数（如 abs(const Complex&)），要访问 Complex 的私有成员（如 real、imag），就必须设为友元，否则无法访问。
2-2：标准库 std::complex 是否把 abs 设为友元？（查阅 cppreference后回答）
否。
查阅 cppreference std::complex可知，abs 是一个普通的非友元函数，通过公有接口（如 real()、imag()）访问数据，不需要友元。
2-3：什么时候才考虑使用 friend？总结你的思考。
-
只有当非成员函数需要访问类的私有或保护成员时，才考虑使用
friend。 -
如果可以通过公有接口完成操作，则不建议用
friend，这样更安全、封装性更好。 -
友元常用于：
-
运算符重载（如
operator<<） -
需要高效访问内部数据的工具函数
-
两个类之间需要紧密协作时
-
问题3:
如果构造对象时禁用=形式，即遇到Complex c4 = c2;编译报错，类Complex的设计应如何调整？
-
需要为
Complex类实现拷贝构造函数Complex(const Complex& other); -
如果没有显式定义，编译器会自动生成一个默认的拷贝构造函数。但如果你显式禁用了或声明了其他构造函数，建议补充拷贝构造函数。
实验任务3:
源码:
PlayerControl.h
#pragma once
#include <string>
enum class ControlType
{
Play,
Pause,
Next,
Prev,
Stop,
Unknown
};
class PlayerControl
{
public:
PlayerControl();
ControlType parse(const std::string &control_str);
void execute(ControlType cmd) const;
static int get_cnt();
private:
static int total_cnt;
};
PlayerControl.cpp
#include "PlayerControl.h"
#include <iostream>
#include <algorithm>
#include <cctype>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
ControlType PlayerControl::parse(const std::string &control_str)
{
std::string lower_str = control_str;
std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(),
[](unsigned char c)
{ return std::tolower(c); });
ControlType type = ControlType::Unknown;
if (lower_str == "play")
{
type = ControlType::Play;
}
else if (lower_str == "pause")
{
type = ControlType::Pause;
}
else if (lower_str == "next")
{
type = ControlType::Next;
}
else if (lower_str == "prev")
{
type = ControlType::Prev;
}
else if (lower_str == "stop")
{
type = ControlType::Stop;
}
if (type != ControlType::Unknown)
{
total_cnt++;
}
return type;
}
void PlayerControl::execute(ControlType cmd) const
{
switch (cmd)
{
case ControlType::Play:
std::cout << "[play] Playing music...\n";
break;
case ControlType::Pause:
std::cout << "[Pause] Music paused\n";
break;
case ControlType::Next:
std::cout << "[Next] Skipping to next track\n";
break;
case ControlType::Prev:
std::cout << "[Prev] Back to previous track\n";
break;
case ControlType::Stop:
std::cout << "[Stop] Music stopped\n";
break;
default:
std::cout << "[Error] unknown control\n";
break;
}
}
int PlayerControl::get_cnt()
{
return total_cnt;
}
task3.cpp
#include "PlayerControl.h"
#include <iostream>
void test()
{
PlayerControl controller;
std::string control_str;
std::cout << "Enter Control: (play/pause/next/prev/stop/quit):\n";
while (std::cin >> control_str)
{
if (control_str == "quit")
break;
ControlType cmd = controller.parse(control_str);
controller.execute(cmd);
std::cout << "Current Player control: " << PlayerControl::get_cnt() << "\n\n";
}
}
int main()
{
test();
return 0;
}
运行测试截图:
思考选做:
源码:
PlayerControl.h
#pragma once
#include <string>
enum class ControlType
{
Play,
Pause,
Next,
Prev,
Stop,
Unknown
};
class PlayerControl
{
public:
PlayerControl();
ControlType parse(const std::string &control_str);
void execute(ControlType cmd) const;
static int get_cnt();
private:
static int total_cnt;
};
PlayerControl.cpp
#include "PlayerControl.h"
#include <iostream>
#include <algorithm>
#include <cctype>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
ControlType PlayerControl::parse(const std::string &control_str)
{
std::string lower_str = control_str;
std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(),
[](unsigned char c)
{ return std::tolower(c); });
ControlType type = ControlType::Unknown;
if (lower_str == "play")
{
type = ControlType::Play;
}
else if (lower_str == "pause")
{
type = ControlType::Pause;
}
else if (lower_str == "next")
{
type = ControlType::Next;
}
else if (lower_str == "prev")
{
type = ControlType::Prev;
}
else if (lower_str == "stop")
{
type = ControlType::Stop;
}
if (type != ControlType::Unknown)
{
total_cnt++;
}
return type;
}
void PlayerControl::execute(ControlType cmd) const
{
switch (cmd)
{
case ControlType::Play:
std::cout << "🎵 Playing music...\n";
break;
case ControlType::Pause:
std::cout << "⏸ Music paused\n";
break;
case ControlType::Next:
std::cout << "⏩ Skipping to next track\n";
break;
case ControlType::Prev:
std::cout << "⏪ Back to previous track\n";
break;
case ControlType::Stop:
std::cout << "⏹ Music stopped\n";
break;
default:
std::cout << "❌ unknown control\n";
break;
}
}
int PlayerControl::get_cnt()
{
return total_cnt;
}
task3.cpp
#include "PlayerControl.h"
#include <iostream>
void test()
{
PlayerControl controller;
std::string control_str;
std::cout << "Enter Control: (play/pause/next/prev/stop/quit):\n";
while (std::cin >> control_str)
{
if (control_str == "quit")
break;
ControlType cmd = controller.parse(control_str);
controller.execute(cmd);
std::cout << "Current Player control: " << PlayerControl::get_cnt() << "\n\n";
}
}
int main()
{
test();
return 0;
}
运行测试截图:
实验任务4:
源码:
Fraction.h
#pragma once
#include <string>
#include <stdexcept>
class Fraction
{
public:
static const std::string doc;
Fraction(int up = 0, int down = 1);
Fraction(const Fraction &other);
int get_up() const;
int get_down() const;
Fraction negative() const;
friend void output(const Fraction &f);
friend Fraction add(const Fraction &f1, const Fraction &f2);
friend Fraction sub(const Fraction &f1, const Fraction &f2);
friend Fraction mul(const Fraction &f1, const Fraction &f2);
friend Fraction div(const Fraction &f1, const Fraction &f2);
private:
int up;
int down;
int gcd(int a, int b) const;
void reduce();
};
Fraction.cpp
#include "Fraction.h"
#include <iostream>
#include <algorithm>
const std::string Fraction::doc = "Fraction类 v0.01版.\n目前仅支持分数对象的构造、输出、加/减/乘/除运算.";
Fraction::Fraction(int up, int down) : up(up), down(down)
{
if (down == 0)
{
throw std::invalid_argument("分母不能为0");
}
reduce();
}
Fraction::Fraction(const Fraction &other) : up(other.up), down(other.down) {}
int Fraction::get_up() const
{
return up;
}
int Fraction::get_down() const
{
return down;
}
Fraction Fraction::negative() const
{
return Fraction(-up, down);
}
int Fraction::gcd(int a, int b) const
{
a = std::abs(a);
b = std::abs(b);
return b == 0 ? a : gcd(b, a % b);
}
void Fraction::reduce()
{
if (down < 0)
{
up = -up;
down = -down;
}
int g = gcd(up, down);
if (g != 0)
{
up /= g;
down /= g;
}
}
void output(const Fraction &f)
{
if (f.down == 1)
{
std::cout << f.up;
}
else
{
std::cout << f.up << "/" << f.down;
}
}
Fraction add(const Fraction &f1, const Fraction &f2)
{
int new_up = f1.up * f2.down + f2.up * f1.down;
int new_down = f1.down * f2.down;
return Fraction(new_up, new_down);
}
Fraction sub(const Fraction &f1, const Fraction &f2)
{
int new_up = f1.up * f2.down - f2.up * f1.down;
int new_down = f1.down * f2.down;
return Fraction(new_up, new_down);
}
Fraction mul(const Fraction &f1, const Fraction &f2)
{
int new_up = f1.up * f2.up;
int new_down = f1.down * f2.down;
return Fraction(new_up, new_down);
}
Fraction div(const Fraction &f1, const Fraction &f2)
{
if (f2.up == 0)
{
throw std::invalid_argument("除数不能为0");
}
int new_up = f1.up * f2.down;
int new_down = f1.down * f2.up;
return Fraction(new_up, new_down);
}
task4.cpp
#include "Fraction.h"
#include <iostream>
void test1();
void test2();
int main()
{
std::cout << "测试1：Fraction类基础功能测试\n";
try
{
test1();
}
catch (const std::exception &e)
{
std::cout << "错误：" << e.what() << std::endl;
}
std::cout << "\n测试2：分母为0测试：\n";
try
{
test2();
}
catch (const std::exception &e)
{
std::cout << "错误：" << e.what() << std::endl;
}
return 0;
}
void test1()
{
using std::cout;
using std::endl;
cout << "Fraction类测试：" << endl;
cout << Fraction::doc << endl
<< endl;
Fraction f1(5);
Fraction f2(3, -4), f3(-18, 12);
Fraction f4(f3);
cout << "f1 = ";
output(f1);
cout << endl;
cout << "f2 = ";
output(f2);
cout << endl;
cout << "f3 = ";
output(f3);
cout << endl;
cout << "f4 = ";
output(f4);
cout << endl;
const Fraction f5(f4.negative());
cout << "f5 = ";
output(f5);
cout << endl;
cout << "f5.get_up() = " << f5.get_up()
<< ", f5.get_down() = " << f5.get_down() << endl;
cout << "f1 + f2 = ";
output(add(f1, f2));
cout << endl;
cout << "f1 - f2 = ";
output(sub(f1, f2));
cout << endl;
cout << "f1 * f2 = ";
output(mul(f1, f2));
cout << endl;
cout << "f1 / f2 = ";
output(div(f1, f2));
cout << endl;
cout << "f4 + f5 = ";
output(add(f4, f5));
cout << endl;
}
void test2()
{
using std::cout;
using std::endl;
Fraction f6(42, 55), f7(0, 3);
cout << "f6 = ";
output(f6);
cout << endl;
cout << "f7 = ";
output(f7);
cout << endl;
cout << "f6 / f7 = ";
try
{
output(div(f6, f7));
}
catch (const std::invalid_argument &e)
{
cout << "分母不能为0";
}
cout << endl;
}
运行测试截图:
回答问题:
分数的输出和计算， 由函数/类+static) output/add/sub/mul/div ，你选择的是哪一种设计方案？（友元/自由函数/命名空间+自由函数/类+static)
你的决策理由？如友元方案的优缺点、静态成员函数方案的适用场景、命名空间方案的考虑因素等。
我选择：命名空间+自由函数方案。
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如果操作不需要访问私有成员，优先用自由函数或命名空间下的自由函数，保证封装性和可维护性。
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如果确实需要访问私有成员，且操作与类紧密相关，可考虑友元，但要控制数量，避免滥用。
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静态成员函数适合工具类、工厂类等场景，但对于分数运算，通常自由函数更灵活。
决策理由：
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友元优点：可访问私有成员，代码简洁。
缺点：破坏封装，增加耦合，维护难度提升。
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静态成员函数优点：归属明确，调用方便。
缺点：不能访问私有成员，只能操作公有接口。
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命名空间方案优点：结构清晰，避免命名冲突，适合扩展。
缺点：实现时仍需通过公有接口访问数据。
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自由函数优点：封装性好，灵活，易于测试和复用。
缺点：有时实现不够高效。
总结：
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