CODEWITHSUNDEEP
c++filestreamseekg
Zasito
Zasito

Reputation: 279

Problems using seekg in C++

I'm reading a file through a function like this:

#include <iostream>
#include <fstream>
#include <string>
...
void readfile(string name){

    string line;
    int p = 0;
    ifstream f(name.c_str());

    while(getline(f,line)){
        p++;
    }
    f.seekg(0);
    cout << p << endl;        

    getline(f,line);
    cout << line << endl;
}

Mi file has 3 lines:

first
second
third

I expected the output:

3
first

Instead I get:

3
(nothing)

why is my seekg not working?

Upvotes: 0

Views: 1281

Answers (2)

Yudaev Alexander
Yudaev Alexander

Reputation: 36

Use iterators for read from the file

std::fstream file( "myfile.txt", std::ios::out );
std::string data = std::string(
     std::istreambuf_iterator<char>( file ),
     std::istreambuf_iterator<char>() );

Upvotes: 0

JAB
JAB

Reputation: 21089

Because seekg() fails if the stream has reached the end of the file (eofbit is set), which occurs due to your getline looping. As sftrabbit implies, calling clear() will reset that bit and should allow you to seek properly. (Or you could just use C++11, in which seekg will clear eofbit itself.)

Upvotes: 3

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