c++ 基于文件的增删改查

╰半夏微凉° 2022-06-05 09:19 264阅读 0赞

wuzhixiang

#include <iostream>
    #include <fstream>
    #include <sstream>
    #include <string>
    #include <iomanip>
    #include <windows.h>
    #define WIDTH 20
    #define space setw(WIDTH)
    #define NEWLINE "\r\n"
    using namespace std;
    
    void write(const char *filename)
    {
        ofstream out;
        out.open(filename,ios::app);
        if(!out.is_open())
        {
            cout<<"open error"<<endl;
            return ;
        }
        else
        {
            int id,age;
            string name;
            cout<<"请输入id、姓名、年龄："<<endl;
            cin>>id>>name>>age;
            out.fill(' ');
            out.setf(ios::left);
            out<<space<<id<<space<<name<<space<<age<<NEWLINE;
            out.close();
            cout<<"添加成功！！"<<endl;
        }
    }
    
    void read(const char *filename)
    {
        ifstream in;
        in.open(filename,ios::in);
        if(!in.is_open())
        {
            cout<<"file open error"<<endl;
            return ;
        }
        else
        {
            stringstream ss;
            char line[100];
            cout.setf(ios::left);
            cout.fill(' ');
            cout<<space<<"id"<<space<<"name"<<space<<"age"<<endl;
            while(in.peek()!=EOF)
            {
                in.getline(line,100);
                ss<<line;
                int id,age;
                string name;
                ss>>id>>name>>age;
                cout<<space<<id<<space<<name<<space<<age<<endl;
                ss.str("");
                ss.clear();
            }
            in.close();
        }
    }
    
    void del(const char *filename)
    {
        int id;
        cout<<"请输入您要删除学生的编号"<<endl;
        cin>>id;
        ifstream in;
        in.open(filename,ios::in);
        if(!in.is_open())
        {
            cout<<"file open error"<<endl;
            return ;
        }
        else
        {
            string temp;
            stringstream ss;
            int curId;;
            while(in.peek()!=EOF)
            {
                string line;
                getline(in,line);
                ss<<line;
                ss>>curId;
                if(curId!=id)
                {
                    temp += line + NEWLINE;
                }
                ss.str("");
                ss.clear();
            }
            in.close();
            ofstream out;
            out.open("G:\\students.txt",ios::out);
            if(!out.is_open())
            {
                cout<<"file open error"<<endl;
                return ;
            }
            else
            {
                out<<temp;
                out.close();
                cout<<"删除成功！！"<<endl;
            }
        }
    
    }
    
    
    
    int search_pos(const char *filename,int id)
    {
        ifstream in;
        in.open(filename,ios::in|ios::binary);
        if(!in.is_open())
        {
            cout<<"file open error"<<endl;
            return -1;
        }
        else
        {
            stringstream ss;
            while(in.peek()!=EOF)
            {
                int start = in.tellg();
                string line;
                getline(in,line);
                ss<<line;
                int curID;
                ss>>curID;
                if(curID == id)
                {
                    in.close();
                    return start;
                }
                ss.str("");
            }
            cout<<"对不起您查找的同学信息不存在!"<<endl;
            in.close();
        }
        return -1;
    }
    
    void search(const char *filename)
    {
        cout<<"请输入您要查找的学生id："<<endl;
        int id;
        cin>>id;
        int pos = search_pos(filename,id);
        string line;
        fstream in;
        in.open(filename,ios::in|ios::binary);
        in.seekg(pos,ios::beg);
        getline(in,line);
        cout.setf(ios::left);
        cout<<space<<"id"<<space<<"name"<<space<<"age"<<endl;
        cout<<line<<endl;
    }
    
    void edit(const char *filename)
    {
        int id,age;
        string name;
        cout<<"请输入您要修改的学生id"<<endl;
        cin>>id;
        cout<<"请输入该学生新的姓名、年龄"<<endl;
        cin>>name>>age;
        stringstream infoTemp;
        infoTemp.fill(' ');
        infoTemp.setf(ios::left);
        infoTemp<<space<<id<<space<<name<<space<<age;
        string newInfo;
        getline(infoTemp,newInfo);
        fstream file;
        file.open(filename,ios::in|ios::out|ios::binary);
        if(!file.is_open())
        {
            cout<<"file open error"<<endl;
            return ;
        }
        else
        {
            int pos = search_pos(filename,id);
            file.seekg(pos,ios::beg);
            file<<newInfo;
            cout<<"修改后信息为："<<endl;
            cout<<newInfo<<endl;
            file.close();
        }
    }
    
    int main()
    {
        const char *filename = "G:\\students.txt";
        while(true)
        {
            cout<<"--------------------------"<<endl;
            cout<<"0、查看全部信息"<<endl;
            cout<<"1、新增学生信息"<<endl;
            cout<<"2、删除学生信息"<<endl;
            cout<<"3、修改学生信息"<<endl;
            cout<<"4、查找学生信息"<<endl;
            int cmd;
            cin>>cmd;
            system("cls");
            switch(cmd)
            {
                case 0:read(filename);break;
                case 1:write(filename);break;
                case 2:del(filename);break;
                case 3:edit(filename);break;
                case 4:search(filename);break;
            }
        }
        return 0;
    }