problems with seekg

[nomad5000]

Hi I'm trying to read a textfile and print it's content twice to the std::cout but it won't work the second time. I think it has something to do with the seekg(0) command but I don't know.

here is my code:
the seekg.cpp file:

#include <iostream>
#include <fstream>
using namespace std;
int main(){
    ifstream in("data.txt",ios::in);
    if(!in){
        cerr<<"file could not be opened"<<endl;
    }
    char line[200];
    while(in.getline(line,200)){
        cout<<line<<endl;
    }
    in.seekg(0);
    while(in.getline(line,200)){
        cout<<line<<endl;
    }    
}
 

the data.txt file:

michael
santiago
carlos
seppi
 

my output is:
$./a
michael
santiago
carlos
seppi
$

[tyreld]

The problem is that the eof bit gets set after the first loop, and any file operations on the stream will now fail. You have to clear the bit by calling the aptly named clear member.

#include <iostream>
#include <fstream>
using namespace std;
int main(){
        ifstream in("data.txt",ios::in);
        if(!in){
                cerr<<"file could not be opened"<<endl;
        }
        char line[200];
        while(in.getline(line,200)){
                cout<<line<<endl;
        }
 
        // Clear the eofbit so we can perform more actions on the stream.
        in.clear();
 
        in.seekg(0, ios::beg);
        while(in.getline(line,200)){
                cout<<line<<endl;
        }
}
 

[nomad5000]

Thank you very much!

One more question. Is there some kind of refference where all thees tricks with files are explained?

[tyreld]

The Bjarne Stroustrup book "The C++ Programming Language (Special Edition)" is probably the best reference for ISO standard C++. However, it isn't exactly the easist book to read.

The following is also a good online quick reference to the iostream library:

C++ Library Reference