关于seekg失效的问题

当file.eof()=1的时候seekg就不好用了，
当file.eof()=0的时候seekg是好用的。

也就是说当一个文件读到尾部以后，
不能再用seekg来移动或者定位了。
通过建立该文件新的对象能解决这个问题。

如果只是输出的话可以用streambuf的rdbuf

#include<fstream>
#include<iostream>
#include<string>
using namespace std;

int main(){
    ofstream ofile("test.txt");
    ofile<<"hello this is testing fstream!";
    ofile<<endl;
    ofile.close();

    ifstream ifile("test.txt");
    string line;
    for(int i=0; i<3; i++){
        cout<<"this is "<<i<<" file"<<endl;
        ifile.clear();
        while(getline(ifile,line)){
            cout<<line<<endl;
        }
        cout<<"eof: "<<ifile.eof()<<endl;
        ifile.seekg(0,ios::beg);
    }
    ifile.close();
}

输出：

this is 0 file
hello this is testing fstream!
eof: 1
this is 1 file
eof: 1
this is 2 file
eof: 1

可以改用rdbuf

#include<fstream>
#include<iostream>
#include<string>
using namespace std;

int main(){
    ofstream ofile("test.txt");
    ofile<<"hello this is testing fstream!";
    ofile<<endl;
    ofile.close();

    ifstream ifile("test.txt");
    string line;
    for(int i=0; i<3; i++){
        cout<<"this is "<<i<<" file"<<endl;
        cout<<ifile.rdbuf();
        cout<<"eof: "<<ifile.eof()<<endl;
        ifile.seekg(0,ios::beg);
    }
    ifile.close();
}

输出：

this is 0 file
hello this is testing fstream!
eof: 0
this is 1 file
hello this is testing fstream!
eof: 0
this is 2 file
hello this is testing fstream!
eof: 0