实验6

3.1 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();
}

3.2 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";
}

更改为char之后：

int类型的数据占用四个字节，而char型的数据只占用一个字节，array<char, N> x中的x只占用5个字节，而array<int, N> x占用20个字节。
  所以在用array<char, N> x中x的地址来读取文件流中的数据，第一个数据97会占用四个字节，97对应的char型数据为a,98为b，只能读取两个数据，而且内存越界了。

vector.hpp:

#include<iostream>
using namespace std;

template<typename T>
class Vector {
private:
    int size;  //储存数据项个数
    T* p;
public:
    Vector(int n):size{n}{ p = new T[size]; }
    Vector(int n, T value): size{ n } 
    {
    p = new T[size];
    for (int i = 0; i < size; i++)
        p[i] = value;
    }
    Vector(const Vector<T>& obj):size{obj.size} 
    {
    p = new T[size];
    for (auto i = 0; i < size; i++)
        p[i] = obj.p[i];
    }
    ~Vector() { delete []p; }
    int get_size() { return size; }
    T &at(int index);
    T &operator[](int i);
    template<typename T1>
    friend void output(const Vector<T1>&p1);
};

template<typename T>
T& Vector<T>::at(int index) {
        if (index >= 0 && index < size)
        return p[index];
}

template<typename T>
T& Vector<T>::operator[](int i) {
    return p[i];
}

template<typename T1>
void output(const Vector<T1>& p1) {
    for (int i = 0; i < p1.size; i++)
        cout << p1.p[i] << ", ";
    cout << "\b\b\n";
}

task4：
#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 * 0.7;

    output(x1);

    Vector<int> x2(n, 42);
    Vector<int> x3(x2);

    output(x2);
    output(x3);

    x2.at(0) = 77;
    output(x2);

    x3[0] = 999;
    output(x3);
}

int main() {
    test();
}

更改task4：
#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 * 0.5;

    output(x1);

    Vector<int> x2(n, 25);
    Vector<int> x3(x2);

    output(x2);
    output(x3);

    x2.at(0) = 101;
    output(x2);

    x3[0] = 333;
    output(x3);
}

int main() {
    test();
}

task5：

#include<fstream>
#include<iostream>
#include<iomanip>
using std::ofstream;
using std::ios_base;
using std::setw;
using namespace std;
void output(std::ostream& out)
{
    char a[26];
    char change1;
    cout << "  ";
    out << "  ";
    for (int i = 0; i < 26; i++)
        a[i] = char(i+65);
    for (int i = 97; i <= 122; i++)
    {
        cout << setw(2) << char(i);
        out << setw(2) << char(i);
    }
    cout << endl;
    out << endl;
    for (int i = 0; i < 26; i++)
    {
        cout << setw(2)<<i + 1;
        out << setw(2) << i + 1;        
        for (int k = 0; k < 25; k++)
        {
            change1 = a[k];
            a[k] = a[k + 1];
            a[k + 1] = change1;
        }
        for (int j = 0; j < 26; j++)
        {
            cout <<setw(2)<< a[j];
            out  << setw(2)<<a[j];
        }
        cout << endl;
        out << endl;
    }
}


int main()
{
    ofstream out;
    out.open("cipher_key.txt", ios::out);
    if (!out.is_open()) {
        std::cout << "fail to open file cipher_key.txt" << std::endl;
        return 1;
    }
    output(out);
    out.close();
}