实验六

6.3

#include <iostream>
#include <fstream>
#include <array>
#define N 5
void test1(){
    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";
        
    }
    // 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();
}
void test2() {
    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";
        
    }
    // 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";
}
int main() {
    test1();
    test2();
    return 0;
}

修改后结果如下：

char型占1个字节，而int型占4个字节。

6.4

#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();
}


#pragma once
#include<iostream>
using namespace std;
template<typename T>
class vector{
    template<typename T>
    friend void output(vector<T>& v);
public:
    vector(int n);
    vector(int n, T value);
    vector(const vector<T>& v) ;
    ~vector()=default;

    T& at(int i) const{ return vec[i]; };
    T& operator[](int i)const { return vec[i]; };
    int get_size()const { return size; };
private:
    int size;
    T* vec;
};

//构造函数接口
template<typename T>
vector<T>::vector(int n) {
    size = n;
    cout << "constructor called \n";
    vec = new T[size];
}
//构造函数接口
template<typename T>
vector<T>::vector(int n, T value) {
    cout << "constructor called" << endl;
    size = n;
    vec = new T[size];
    for (int i = 0; i < size; i++) {
        vec[i] = value;
    }
}
//复制构造函数接口
template<typename T>
vector<T>::vector(const vector<T>& v) {
    cout << "copyconstructor called \n";
    size = v.size;
    vec = new T[size];
    for (int i = 0; i < size; i++)
        vec[i] = v.vec[i];
}

//输出数组元素函数接口
template<typename T>
void output(vector<T>& v) {
    for (int i = 0; i < v.size; i++)
        cout << v.vec[i] << " ";
    cout << endl;
}

6.5

#include<iostream>
#include<fstream>
#include<iomanip>
using namespace std;
void output(std::ostream& output) {
    output << "  ";
    for (int i = 97; i < 123; i++) {
        output << setw(2) << char(i);
    }
    output << endl;
    for (int i = 1; i <= 26; i++) {
        output << setw(2) << i;
        for (int j = i; j < i + 26; j++) {
            output << setw(2) << char(65 + j % 26);
        }
        output << endl;
    }
}
int main() {
    ofstream out;
    output(cout);
    out.open("cipher_key.txt");
    if (!out.is_open()) {
        cout << "fail to open file cipher_key.txt to write\n";
        return 0;
    }
    output(out);
    out.close();
    return 0;
}