实验六 模板类和文件

• task3

  //task3_1.cpp
  #include <iostream>
  #include <fstream>
  #include <array>
  #define N 5
  int main() {
  	using namespace std;
  	array<int, N> x{ 97, 98, 99, 100, 101 };
  	ofstream out;
  	out.open("data1.dat", ios::binary);
  	if (!out.is_open()) {
  		cout << "fail to open data1.dat\n";
  		return 1;
  	}
  	// 把从地址&x开始连续sizeof(x)个字节的数据块以字节数据块方式写入文件data1.txt
  	out.write(reinterpret_cast<char*>(&x), sizeof(x));
  	out.close();
  }
  

  

  //task3_2.cpp
  #include <iostream>
  #include <fstream>
  #include <array>
  #define N 5
  int main() {
  	using namespace std;
  	array<int, N> x;
  	ifstream in;
  	in.open("data1.dat", ios::binary);
  	if (!in.is_open()) {
  		cout << "fail to open data1.dat\n";
  		return 1;
  	}
  	// 从文件流对象in关联的文件data1.dat中读取sizeof(x)字节数据写入&x开始的地址单元
  	in.read(reinterpret_cast<char*>(&x), sizeof(x));
  	in.close();
  	for (auto i = 0; i < N; ++i)
  		cout << x[i] << ", ";
  	cout << "\b\b \n";
  }
  

  

   将task3_2中第八行修改为array<char,N> x,得到的输出结果为：

          

 

 　　　原因：先读取97默认为ascii码，输出a，因为int占4个字节，所以之后连着读取了三个\0，输出0，再读取98默认为ascii码，输出b

• task4

//Vector.hpp
#pragma once

#include<iostream>
using namespace std;
template<typename T>
class Vector
{
public:
    Vector(int n);
    Vector(int n, T value);
    Vector(const Vector<T>& v);
    ~Vector() = default;
    T& at(int index) const;
    int get_size() const;
    T& operator[](int i) const { return p[i]; }
    template<typename T1>
    friend void output(const Vector<T1>& v);
private:
    T* p;
    int size;
};

template<typename T>
Vector<T>::Vector(int n) :size{ n }
{
    p = new T[size];
}
template<typename T>
Vector<T>::Vector(int n, T value) : size{ n }
{
    p = new T[size];
    for (auto i = 0; i < size; i++)
        p[i] = value;
}
template<typename T>
Vector<T>::Vector(const Vector& v)
{
    size = v.size;
    p = new T[size];
    for (auto i = 0; i < size; i++)
        p[i] = v.p[i];
}
template<typename T>
T& Vector<T>::at(int index) const
{
    return p[index];
}
template<typename T>
int Vector<T>::get_size() const
{
    return size;
}
template<typename T1>
void output(const Vector<T1>& v)
{
    for (auto i = 0; i < v.size; i++)
        cout << v.p[i] << ",";
    cout << "\b " << endl;
}

　　

//task4.cpp
#include <iostream>
#include "Vector.hpp"
void test() {
	using namespace std;
	int n;
	cin >> n;
	Vector<double> x1(n);
	for (auto i = 0; i < n; ++i)
		x1.at(i) = i * 1.3;
	output(x1);
	Vector<int> x2(n, 42);
	Vector<int> x3(x2);
	output(x2);
	output(x3);
	x2.at(0) = 25;
	output(x2);
	x3[0] = 897;
	output(x3);
}
int main() {
	test();
}

　　

 

•  task5

 

#include<iostream>
#include<iomanip>
#include<fstream>
#define N 26
void output(std::ostream& out) {
	using namespace std;
	char a[N][N];
	cout << "  ";
	out << "  ";
	for (char i = 'a'; i <= 'z'; i++) {
			cout << setw(2) << i;
			out << setw(2) << i;
	}
	cout << endl;
	out << endl;
	for (int i = 0; i < N; i++) {
		cout << setw(2) << i+1;
		out << setw(2) << i+1;
		for (int j = 0; j < N; j++) {
			a[i][j] = (char)(65 + (i + j + 1) % 26);
			cout << setw(2) << a[i][j];
			out << setw(2) << a[i][j];
		}
		cout << endl;
		out << endl;
	}
}
int main() {
	using namespace std;
	ofstream out;
	out.open("cipher_key.txt");
	if (!out.is_open()) {
		cout << "fail to open cipher_key.txt\n";
		return 1;
	}
	output(out);
	out.close();
}