实验六

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};
    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;
    }

    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();

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

改动后

 在写入文件时写入int类型，在内存中占4个字节，读入文件时读入char类型，在内存中占一个字节。

所以读入后会有三个字节的空缺空间。

Vector.hpp

#include<bits/stdc++.h>
using namespace std;
template <class T>
class Vector{
	public:
	Vector(int n);
	Vector(int n,T v);
	~Vector();
	Vector(Vector<T>& v);
	int get_size()const;
	T &at(int index);
	T &operator[](int index);
	 template<class A> friend void output(Vector<A> &xx);
	 private:
	 	int size;
	 	T *a;
}; 
template <class T>
Vector<T>::Vector(int n):size{n}{
   //  cout<<"constructor 1 called."<<endl;
     a = new T[n];
}
template <class T>
Vector<T>::Vector(int n,T v):size{n}{
  //  cout<<"constructor 2 called."<<endl;
    a = new T[n];
    for(int i=0;i<n;i++)
    a[i] = v;
}
template <class T>
Vector<T>::Vector(Vector<T>& v){
//	cout<<"copy constructor  called."<<endl;
	size = v.size;
	a = new T[size];
	for(int i=0;i<size;i++)
    a[i] = v[i];
}
template <class T>
Vector<T>::~Vector(){ 
      delete[] a;
     // cout<<"destructor called."<<endl;
}
template <class T>
int Vector< T>::get_size()const{
    return size;
}
template <class T>
T &Vector<T>::at(int index){
	return a[index];
}
template <class T>
T &Vector<T>::operator[](int index){
    assert(index >= 0 && index < size);
    return a[index];
}
template<class A>
void output(Vector<A> &xx){
    for(int i=0;i<xx.get_size();i++)
    cout<<xx[i]<<" ";
    cout<<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 * 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();
}

task5.cpp

#include<bits/stdc++.h>
using namespace std;
void output(std::ofstream &out)
{   
   int i,j;
	out.open("cipher_key.txt");
	if(!out.is_open()) {
       cout << "fail to open cipher_key.txt\n";
       return;
    }
     for(i=0;i<27;i++){
       //
       if(i==0){
       cout<<setw(2)<<" ";
       out<<setw(2)<<" ";
       for(j=97;j<123;j++){  
       cout<<setw(2)<<char(j);
       out<<setw(2)<<char(j);
	   }
       cout << endl;
       out<< endl;  
		 
	   }
	   
    else{
    	for(j=0;j<27;j++){ 
	 if(j==0){
	   cout<<setw(2)<<i;
	   out<<setw(2)<<i;
	   continue;
	   }
	   cout<<setw(2)<<char(65+(i+j-1)%26);
		out<<setw(2)<<char(65+(i+j-1)%26);
	}
		cout<<endl;
		out<<endl;
    }
}
	
	out.close();	

}
int main(){
	ofstream out;
   	output(out);
}

小结

任务4中，对于友元函数的模板类声明必须换一个模板类字符。对每个成员函数类外定义前也要声明模板类。

任务五中，按行写入文件，基本思路是输出一行写一行。对于这种矩阵的基本循环控制也要熟悉。