Thread: Creating a read/write file

I want to create a read/write file.Whenever I open it(even if it already exists) I want it to truncate itself.

The only way I found how to do it was via a streambuf from the book 'Thinking in C++':

Code:

#include "../require.h"
#include <iostream>
#include <fstream>

using namespace std;

int main() {
    ifstream in("Iofile.cpp");
    assure(in, "Iofile.cpp");
    ofstream out("Iofile.out");
    assure(out, "Iofile.out");
    out << in.rdbuf(); // Copy file
    in.close();
    out.close();
    
    // Open for reading and writing:
    ifstream in2("Iofile.out", ios::in | ios::out);
    assure(in2, "Iofile.out");
    ostream out2(in2.rdbuf());
    cout << in2.rdbuf(); // Print whole file
    out2 << "Where does this end up?";
    out2.seekp(0, ios::beg);
    out2 << "And what about this?";
    in2.seekg(0, ios::beg);
    cout << in2.rdbuf();
} ///:~

I don't want to use a streambuf so I tried the following:

Code:

#include <fstream>
#include <string>

using namespace std;

int main() {

    fstream out("Texttest.txt",ios::out|ios::in|ios::trunc);
    ifstream in("Text.txt");
    out<<in.rdbuf();
    out.seekp(0,ios::beg);
    string s;
    out>>s;
    cout<<s;
    cin.get();
}

When I run it prints on the screen ZKM7461(see below the file Text.txt).This happen for every execution,as it should be.

But when i run it with the file 'test21.txt' replacing the file 'Text.txt'
it prints 'Ë212324' whenever it wants.Some times it prints it,some others it doesn't print anything.
What is happaning?
Are there any other suggestions in how I could have a read/write file the way I want it to be?

Text.txt:

ZKM7461 FORD Ka
YRM3245 TOYOTA Corolla
ET9672 PEUGEOT 204
ZZO7563 PEUGEOT 206

test21.txt:

Ë212324 ÐÅÔÑÏÓ ÁÍÁÃÍÏÕ Ìõñóßíçò 3 15765 1
Á124456 ÓÐÕÑÏÓ ÐÅÔÑÏÕ ÄïéñÜíçò 8 34489 0
Â456765 ÇËÉÁÓ ÁÍÁÓÔÁÓÉÏÕ Åëðßäïò 14 15568 1
Æ455467 ÁÍÄÑÅÁÓ ÊÁËÏÓ ÁèçíÜò 35 16472 1
×789342 ÉÙÁÍÍÇÓ ÔÓÁÍÁÊÁÓ ÊïñõôóÜò 68 32467 0
Ë343434 ÁÍÔÙÍÇÓ ÓÔÁÌÏÕ ÐåñéêëÝïõò 2 32256 1
Ô565678 ÊÙÓÔÁÓ ÐÁÐÐÁÓ ÐáëáìÜ 87 44566 1