实验3
实验任务1
源代码：
button.hpp:
#pragma once #include <iostream> #include <string> class Button { public: Button(const std::string &label_); const std::string& get_label() const; void click(); private: std::string label; }; Button::Button(const std::string &label_): label{label_} { } inline const std::string& Button::get_label() const { return label; } inline void Button::click() { std::cout << "Button '" << label << "' clicked\n"; }
window.hpp:
#pragma once #include <iostream> #include <vector> #include <algorithm> #include "button.hpp" class Window{ public: Window(const std::string &title_); void display() const; void close(); void add_button(const std::string &label); void click_button(const std::string &label); private: bool has_button(const std::string &label) const; private: std::string title; std::vector<Button> buttons; }; Window::Window(const std::string &title_): title{title_} { buttons.push_back(Button("close")); } inline void Window::display() const { std::string s(40, '*'); std::cout << s << std::endl; std::cout << "window : " << title << std::endl; int cnt = 0; for(const auto &button: buttons) std::cout << ++cnt << ". " << button.get_label() << std::endl; std::cout << s << std::endl; } inline void Window::close() { std::cout << "close window '" << title << "'" << std::endl; click_button("close"); } inline bool Window::has_button(const std::string &label) const { for(const auto &button: buttons) if(button.get_label() == label) return true; return false; } inline void Window::add_button(const std::string &label) { if(has_button(label)) std::cout << "button " << label << " already exists!\n"; else buttons.push_back(Button(label)); } inline void Window::click_button(const std::string &label) { for(auto &button:buttons) if(button.get_label() == label) { button.click(); return; } std::cout << "no button: " << label << std::endl; }
task1.cpp:
#include "window.hpp" #include <iostream> void test(){ Window w("Demo"); w.add_button("add"); w.add_button("remove"); w.add_button("modify"); w.add_button("add"); w.display(); w.close(); } int main() { std::cout << "用组合类模拟简单GUI:\n"; test(); }
运行结果截图：
问题1：
window和Button是组合关系，window中有vector<Button>
问题2：
（1）优点：这个函数可以被外部调用；风险：破坏了类的封装性，会导致内部消息泄露给外部
（2）如果这个成员函数功能会在类外部被用到，并且需要被用户直接使用，则为public；如果这个函数只会在类内被使用，且易破坏对象状态，则为private
问题3：
接口1直接引用，性能高，使用const，数据无法被外部修改，安全性高
接口2需要额外复制，性能不高，使用const，安全性高
问题4：
程序可以正常运行，push_back先构造临时对象，再将其插入容器尾部，emplace_back直接在容器尾部的内存位置原地构造对象，无需临时对象，效率更高
实验任务2
源代码：
task2.cpp:
#include <iostream> #include <vector> void test1(); void test2(); void output1(const std::vector<int> &v); void output2(const std::vector<int> &v); void output3(const std::vector<std::vector<int>>& v); int main() { std::cout << "深复制验证1: 标准库vector<int>\n"; test1(); std::cout << "\n深复制验证2: 标准库vector<int>嵌套使用\n"; test2(); } void test1() { std::vector<int> v1(5, 42); const std::vector<int> v2(v1); std::cout << "**********拷贝构造后**********\n"; std::cout << "v1: "; output1(v1); std::cout << "v2: "; output1(v2); v1.at(0) = -1; std::cout << "**********修改v1[0]后**********\n"; std::cout << "v1: "; output1(v1); std::cout << "v2: "; output1(v2); } void test2() { std::vector<std::vector<int>> v1{{1, 2, 3}, {4, 5, 6, 7}}; const std::vector<std::vector<int>> v2(v1); std::cout << "**********拷贝构造后**********\n"; std::cout << "v1: "; output3(v1); std::cout << "v2: "; output3(v2); v1.at(0).push_back(-1); std::cout << "**********修改v1[0]后**********\n"; std::cout << "v1: \n"; output3(v1); std::cout << "v2: \n"; output3(v2); } void output1(const std::vector<int> &v) { if(v.size() == 0) { std::cout << '\n'; return; } std::cout << v.at(0); for(auto i = 1; i < v.size(); ++i) std::cout << ", " << v.at(i); std::cout << '\n'; } void output2(const std::vector<int> &v) { if(v.size() == 0) { std::cout << '\n'; return; } auto it = v.begin(); std::cout << *it; for(it = v.begin()+1; it != v.end(); ++it) std::cout << ", " << *it; std::cout << '\n'; } void output3(const std::vector<std::vector<int>>& v) { if(v.size() == 0) { std::cout << '\n'; return; } for(auto &i: v) output2(i); }
运行结果截图：
问题1：
std::vector<int> v1(5, 42);构造v1,含有5个42，const std::vector<int> v2(v1);复制v1到v2，因此v2也有5个42
问题2：
v1.size()为2，v2.size()为2，v1[0].size()为3
问题3：
能实现同等效果，v1.at(0)=-1会检查边界，更安全，而v1[0]=-1不会，安全性较低
问题4：
（1）能输出-1，r为v1.at(0)的引用，r.at(r.size()-1)为r的最后一位，即为-1
（2）直接引用，效率更高，但不能修改
问题5：
（1）深复制，将v1修改后，v2没变
（2）当v是vector时v.at(0)返回值类型为int&,当v是const vector时，v.at(0)返回值类型为const int&，所以at()必须提供带const修饰的重载版本以满足const对象的需要
实验任务3
源代码：
vectorlnt.hpp:
#pragma once #include <iostream> class vectorInt{ public: vectorInt(); vectorInt(int n_); vectorInt(int n_, int value); vectorInt(const vectorInt &vi); ~vectorInt(); int size() const; int& at(int index); const int& at(int index) const; vectorInt& assign(const vectorInt &vi); int* begin(); int* end(); const int* begin() const; const int* end() const; private: int n; int *ptr; }; vectorInt::vectorInt():n{0}, ptr{nullptr} { } vectorInt::vectorInt(int n_): n{n_}, ptr{new int[n]} { } vectorInt::vectorInt(int n_, int value): n{n_}, ptr{new int[n_]} { for(auto i = 0; i < n; ++i) ptr[i] = value; } vectorInt::vectorInt(const vectorInt &vi): n{vi.n}, ptr{new int[n]} { for(auto i = 0; i < n; ++i) ptr[i] = vi.ptr[i]; } vectorInt::~vectorInt() { delete [] ptr; } int vectorInt::size() const { return n; } const int& vectorInt::at(int index) const { if(index < 0 || index >= n) { std::cerr << "IndexError: index out of range\n"; std::exit(1); } return ptr[index]; } int& vectorInt::at(int index) { if(index < 0 || index >= n) { std::cerr << "IndexError: index out of range\n"; std::exit(1); } return ptr[index]; } vectorInt& vectorInt::assign(const vectorInt &vi) { if(this == &vi) return *this; int *ptr_tmp; ptr_tmp = new int[vi.n]; for(int i = 0; i < vi.n; ++i) ptr_tmp[i] = vi.ptr[i]; delete[] ptr; n = vi.n; ptr = ptr_tmp; return *this; } int* vectorInt::begin() { return ptr; } int* vectorInt::end() { return ptr+n; } const int* vectorInt::begin() const { return ptr; } const int* vectorInt::end() const { return ptr+n; }
task3.cpp:
#include "vectorInt.hpp" #include <iostream> void test1(); void test2(); void output1(const vectorInt &vi); void output2(const vectorInt &vi); int main() { std::cout << "测试1: \n"; test1(); std::cout << "\n测试2: \n"; test2(); } void test1() { int n; std::cout << "Enter n: "; std::cin >> n; vectorInt x1(n); for(auto i = 0; i < n; ++i) x1.at(i) = (i+1)*10; std::cout << "x1: "; output1(x1); vectorInt x2(n, 42); vectorInt x3(x2); x2.at(0) = -1; std::cout << "x2: "; output1(x2); std::cout << "x3: "; output1(x3); } void test2() { const vectorInt x(5, 42); vectorInt y; y.assign(x); std::cout << "x: "; output2(x); std::cout << "y: "; output2(y); } void output1(const vectorInt &vi) { if(vi.size() == 0) { std::cout << '\n'; return; } std::cout << vi.at(0); for(auto i = 1; i < vi.size(); ++i) std::cout << ", " << vi.at(i); std::cout << '\n'; } void output2(const vectorInt &vi) { if(vi.size() == 0) { std::cout << '\n'; return; } auto it = vi.begin(); std::cout << *it; for(it = vi.begin()+1; it != vi.end(); ++it) std::cout << ", " << *it; std::cout << '\n'; }
运行结果截图：
问题1：
版本2先释放了内存，在分配新内存，此时vi就是assign指向的对象，vi.ptr指向的是已经释放的内存，存在问题
问题2：
（1）static_cast<const vectorInt*>(this)的作用是将this指针从vectorInt*类型转换为const vectorInt*类型,转换目的是转换后可以使用const类型
（2）const_caet<int&>的作用是将const int&类型转换为int&类型，转换目的是使其可以修改
问题3：
（1）非const类型调用v1，const类型调用v2
问题4：
可以，std::fill_n(ptr, n, value);功能是将ptr后的n个元素赋值为value；std::copy_n(vi.ptr, vi.n, ptr);功能是将vi.ptr后的vi.n个元素复制到ptr；std::copy_n(vi.ptr, vi.n, ptr_tmp);功能是将vi.ptr后的vi.n个元素复制到ptr_tmp
实验任务4
源代码：
matrix.hpp:
#pragma once #include <iostream> #include <algorithm> #include <cstdlib> class Matrix { public: Matrix(int rows_, int cols_, double value = 0); Matrix(int rows_, double value = 0); Matrix(const Matrix &x); ~Matrix(); void set(const double *pvalue, int size); void clear(); const double& at(int i, int j) const; double& at(int i, int j); int rows() const; int cols() const; void print() const; private: int n_rows; int n_cols; double *ptr; };
matrix.cpp:
#include <iostream> #include <cstdlib> #include "matrix.hpp" Matrix::Matrix(int rows_, int cols_, double value):n_rows(rows_),n_cols(cols_),ptr(new double[rows_*cols_]){ for(int i=0;i<rows_*cols_;i++){ ptr[i]=value; } } Matrix::Matrix(int rows_, double value):n_rows(rows_),n_cols(rows_),ptr(new double[rows_*rows_]){ for(int i=0;i<rows_*rows_;i++){ ptr[i]=value; } } Matrix::Matrix(const Matrix &x):n_rows(x.n_rows),n_cols(x.n_cols),ptr(new double[x.n_rows*x.n_cols]){ for(int i=0;i<x.n_rows*x.n_cols;i++){ ptr[i]=x.ptr[i]; } } Matrix::~Matrix(){ delete[] ptr; } void Matrix::set(const double *pvalue, int size){ if(size!=n_rows*n_cols){ std::cout<<"error"; return; } else{ for(int i=0;i<n_rows*n_cols;i++){ ptr[i]=pvalue[i]; } } } void Matrix::clear(){ for(int i=0;i<n_rows*n_cols;i++){ ptr[i]=0; } } const double& Matrix::at(int i, int j) const{ if(i<0||i>=n_rows||j<0||j>=n_cols){ std::cout<<"error"; } else{ return ptr[i*n_cols+j]; } } double& Matrix::at(int i, int j){ if(i<0||i>=n_rows||j<0||j>=n_cols){ std::cout<<"error"; } else{ return ptr[i*n_cols+j]; } } int Matrix::rows() const{ return n_rows; } int Matrix::cols() const{ return n_cols; } void Matrix::print() const{ for(int i=0;i<n_rows;i++){ for(int j=0;j<n_cols;j++){ std::cout<<at(i,j); if(j<n_cols-1){ std::cout<<", "; } } std::cout<<"\n"; } }
task4.cpp:
#include <iostream> #include <cstdlib> #include "matrix.hpp" void test1(); void test2(); void output(const Matrix &m, int row_index); int main() { std::cout << "测试1: \n"; test1(); std::cout << "\n测试2: \n"; test2(); } void test1() { double x[1000] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; int n, m; std::cout << "Enter n and m: "; std::cin >> n >> m; Matrix m1(n, m); m1.set(x, n*m); Matrix m2(m, n); m2.set(x, m*n); Matrix m3(n); m3.set(x, n*n); std::cout << "矩阵对象m1: \n"; m1.print(); std::cout << "矩阵对象m2: \n"; m2.print(); std::cout << "矩阵对象m3: \n"; m3.print(); } void test2() { Matrix m1(2, 3, -1); const Matrix m2(m1); std::cout << "矩阵对象m1: \n"; m1.print(); std::cout << "矩阵对象m2: \n"; m2.print(); m1.clear(); m1.at(0, 0) = 1; std::cout << "m1更新后: \n"; std::cout << "矩阵对象m1第0行 "; output(m1, 0); std::cout << "矩阵对象m2第0行: "; output(m2, 0); } void output(const Matrix &m, int row_index) { if(row_index < 0 || row_index >= m.rows()) { std::cerr << "IndexError: row index out of range\n"; exit(1); } std::cout << m.at(row_index, 0); for(int j = 1; j < m.cols(); ++j) std::cout << ", " << m.at(row_index, j); std::cout << '\n'; }
运行结果截图：
实验任务5
源代码：
contact.hpp:
#pragma once #include <iostream> #include <string> class Contact { public: Contact(const std::string &name_, const std::string &phone_); const std::string &get_name() const; const std::string &get_phone() const; void display() const; private: std::string name; std::string phone; }; Contact::Contact(const std::string &name_, const std::string &phone_):name{name_}, phone{phone_} { } const std::string& Contact::get_name() const { return name; } const std::string& Contact::get_phone() const { return phone; } void Contact::display() const { std::cout << name << ", " << phone; }
contactBook.hpp:
# pragma once #include <iostream> #include <string> #include <vector> #include <algorithm> #include "contact.hpp" class ContactBook { public: void add(const std::string &name, const std::string &phone); void remove(const std::string &name); void find(const std::string &name) const; void display() const; size_t size() const; private: int index(const std::string &name) const; void sort(); private: std::vector<Contact> contacts; }; void ContactBook::add(const std::string &name, const std::string &phone) { if(index(name) == -1) { contacts.push_back(Contact(name, phone)); std::cout << name << " add successfully.\n"; sort(); return; } std::cout << name << " already exists. fail to add!\n"; } void ContactBook::remove(const std::string &name) { int i = index(name); if(i == -1) { std::cout << name << " not found, fail to remove!\n"; return; } contacts.erase(contacts.begin()+i); std::cout << name << " remove successfully.\n"; } void ContactBook::find(const std::string &name) const { int i = index(name); if(i == -1) { std::cout << name << " not found!\n"; return; } contacts[i].display(); std::cout << '\n'; } void ContactBook::display() const { for(auto &c: contacts) { c.display(); std::cout << '\n'; } } size_t ContactBook::size() const { return contacts.size(); } int ContactBook::index(const std::string &name) const{ for(int i=0;i<contacts.size();i++){ if(contacts[i].get_name()==name){ return i; } } return -1; } bool comparename(Contact &a,Contact &b){ return a.get_name()<b.get_name(); } void ContactBook::sort(){ std::sort(contacts.begin(),contacts.end(),comparename); }
task5.cpp:
#include "contactBook.hpp" void test() { ContactBook contactbook; std::cout << "1. add contacts\n"; contactbook.add("Bob", "18199357253"); contactbook.add("Alice", "17300886371"); contactbook.add("Linda", "18184538072"); contactbook.add("Alice", "17300886371"); std::cout << "\n2. display contacts\n"; std::cout << "There are " << contactbook.size() << " contacts.\n"; contactbook.display(); std::cout << "\n3. find contacts\n"; contactbook.find("Bob"); contactbook.find("David"); std::cout << "\n4. remove contact\n"; contactbook.remove("Bob"); contactbook.remove("David"); } int main() { test(); }
运行结果截图：
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