ios_base::ate and cleaning file

Question

Help please, code execution outputs instead of

just

Why the file is cleared before writing? Trunc not set

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    ofstream a{ "1.txt",ios_base::ate };
    a << "123";
    a.close();
    ofstream b{ "1.txt",ios_base::ate };
    b << "456";
    b.close();
    ifstream c{ "1.txt" };
    string str;
    c >> str;
    cout << str;
    return 0;
}

Simply read the documentation for the functions you use. The documentation is very clear about what they do. -1 — Lightness Races in Orbit, Jul 11 '16 at 00:29

score 0 · Answer 1 · edited May 23 '17 at 12:14

You need to use app in your second writer to append the content to the file instead of rewritting it, as follows:

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    ofstream a{ "1.txt",ios_base::ate };
    a << "123";
    a.close();
    ofstream b{ "1.txt",ios_base::app }; //notice here is app instead of ate
    b << "456";
    b.close();
    ifstream c{ "1.txt" };
    string str;
    c >> str;
    cout << str;
    return 0;
}

As in this question :

std::ios_base::ate does NOT imply std::ios_base::app

So if you use ate it does not mean that it will append the content to the file.

score 0 · Answer 2 · edited May 23 '17 at 12:32

0

You can find the different between ios_base:ate and ios_base:app here

For your code, you can change it like this:

ofstream b {"1.txt", ios_base:app};

edited May 23 '17 at 12:32

Community

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answered Jul 11 '16 at 02:12

GAVD

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ios_base::ate and cleaning file

2 Answers2