c++ 文件流

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
using namespace std;
class A{
    string name;
    int age;
public:
    A()=default;
    A(string name,int age):name(name),age(age){};
    string getName()const{
        return name;
    }
    int getAge()const{
        return age;
    }
    virtual ~A(){};
};
int main()
{
    fstream file("D:\\a.txt",ios::in|ios::out|ios::trunc);
    vector<A> v(3,{"张三",1}),ans;
    if(!file) cerr<<"file打开失败"<<endl;
    for(const auto it:v) file<<it.getName()<<" "<<it.getAge()<<endl;
    file.seekg(0,ios::beg);
    string line;
    while(getline(file,line)){
        istringstream iss(line);
        string name,age;
        iss>>name>>age;
        ans.push_back({name,atoi(age.c_str())});
    }
    for(const auto it:ans) cout<<it.getName()<<" "<<it.getAge()<<endl;
    file.close();
    return 0;
}