Thread: tellg() returning -1

tellg() won't return the size of the file, it returns -1.
What is the reason for it?

Code:

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

fstream file;

int main()
{
    // Creat file
    ofstream outfile("test.txt");
    outfile.close();

    string str ;
    file.open("test.txt", fstream::in | fstream::out);
    if (!file.is_open())
    {
        cerr << "Error opening file." << endl;
        return 1;
    }

    file << "Hello World." << endl;
    file.seekg (0, ios::beg);

    while(!file.eof()) 
    {
        getline(file, str); 
        cout << str << endl; 
    }

    file.seekg(0, ios::end);
    int newsize = file.tellg();
    file.seekg(0, ios::beg);
    cout << newsize << endl;

    file.close();

    return 0;
}