实验6 模板类和文件OL

task3-1

#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

#include <iostream>
#include <fstream>
#include <array>
#define N 5

int main() {
    using namespace std;
    array<int, N> x;
    /*array<char, N> x;*/

    ifstream in;
    in.open("data1.dat", ios::binary);
    if (!in.is_open()) {
        cout << "fail to open data1.dat\n";
        return 1;
    }

    in.read(reinterpret_cast<char*>(&x), sizeof(x));
    in.close();

    // 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
    for (auto i = 0; i < N; ++i)
        cout << x[i] << ", ";
    cout << "\b\b \n";
}

实验结果为：

array<int, N> x; ----> 修改成: array<char, N> x;

修改之后的实验结果为：

出现该结果的主要原因为，修改之前array进行读取文件的时候，针对的是整型，从文本中就依次读取97 98 99 100 101

但在修改之后array在读取的时候，针对的是单个字符，其在内存中所占取的大小为一个字节，而文件中的为整数，而每个整数占取得是4个字节，在读取的会依次读取97 0 0 0 98，所以出现了上述的情况。

task4 Vector.h

#pragma once

#include<iostream>

using namespace std;

template<typename T>
class Vector {
public:
    Vector(int n);
    Vector(int n, T value);
    Vector(const Vector& vp);
    ~Vector();

public:
    T& at(int index);

    T get_size(T p[]) { return sizeof(p); }

    friend void output(Vector& x){
    for (auto i = 0; i < x.size; i++)
        cout << x.p[i] << ", ";
    cout << "\b\b \n";
    }

    T& operator[](int index) {
        return p[index];
    }

private:
    int size;
    T* p;
};

template<typename T>
Vector<T>::Vector(int n) :size{ n } {
    p = new T[n];
}

template<typename T>
Vector<T>::Vector(int n, T value) :size{ n } {
    p = new T[n];
    for (auto i = 0; i < n; i++) {
        p[i] = value;
    }
}

template<typename T>
Vector<T>::Vector(const Vector& vp) :size{ vp.size } {
    p = new int[size];
    for (auto i = 0; i < size; ++i) {
        p[i] = vp.p[i];
    }
}

template <typename T>
Vector<T>::~Vector()
{
    delete[] p;
}

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

task4.cpp

#include <iostream>
#include "Vector.h"

void test() {
    using namespace std;

    int n;
    cin >> n;

    Vector<double> x1(n);
    for (auto i = 0; i < n; ++i)
        x1.at(i) = i * 0.8;

    output(x1);

    Vector<int> x2(n, 44);
    Vector<int> x3(x2);

    output(x2);
    output(x3);

    x2.at(0) = 88;
    output(x2);

    x3[0] = 888;
    output(x3);
}

int main() {
    test();
}

实验结果：

task 6

#include<iostream>
#include<fstream>
#include<iomanip>

using namespace std;


void output(ostream& out) {
    char a[27][27];
    a[0][0] = ' ';
    for (int i = 1; i < 27; i++) {
        a[0][i] = 'a' + i - 1;
        a[i][0] = '0' + i;
    }

    int n = 0;
    for (int i = 1; i < 27; i++) {
        n = i;
        for (int j = 1; j < 27; j++) {
            if (65 + n > 90)
            {
                a[i][j] = 'A' + n - 26;
            }
            else {
                a[i][j] = 'A' + n;
            }
            n++;
        }
    }
    for (int i = 0; i < 27; i++) {
        if (i == 0) {
            cout <<setw(2) <<' ';
        }
        else {
            cout << setw(2) << a[i][0]-'0';
            out << setw(2) << a[i][0]-'0';
        }
        for (int j = 1; j < 27; j++) {
            cout << setw(2) << a[i][j];
            out << setw(2) << a[i][j];
        }
        cout << endl;
        out << endl;
    }
}


int main() {
    ofstream out;
    out.open("cipher_key.txt");
    if (!out.is_open())
    {
        cout << "fail to open data1.dat\n";
        return 1;
    }
    output(out);
    out.close();
}

实验结果：