ostream usage in C++

Question

I have a program showing error. How to resolve the error and to use ostream to display output I use g++ compiler in my ubuntu

#include<iostream>
using namespace std;
int main()
{
    ostream out;
    out<<"Hello World";
}

What is the error? (Aside from the fact that you probably should have used `std::cout`) — Daniel Fischer, Jan 05 '12 at 13:30
Have a look on this similar question http://stackoverflow.com/questions/524524/creating-an-ostream — Amit, Jan 05 '12 at 13:31

score 4 · Accepted Answer · answered Jan 05 '12 at 13:32

4

The ostream that you want (attached to the display) has already been defined as cout.

#include<iostream>
using namespace std;
int main()
{
    cout<<"Hello World";
}

Not all ostreams send the stream to the terminal display.

answered Jan 05 '12 at 13:32

Drew Dormann

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score 2 · Answer 2 · answered Jan 05 '12 at 13:35

2

std::ostream does not have a default constructor, this:

ostream out;

will be a compile time error.

You are probably wanting to use std::cout (as has already been stated).

answered Jan 05 '12 at 13:35

hmjd

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score 2 · Answer 3 · answered Jan 05 '12 at 14:00

Firstly, include #include <fstream> . Secondly, change ofstream out to ofstream out("file.txt") .

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

int main () {

  ofstream out ("c:\\test5.txt");
  out<<"Hello World";
  out.close();

  return 0;
}

score 0 · Answer 4 · answered Jan 05 '12 at 13:42

In order to do some output you need to get the right ostream. As Drew Dormann showed you, you can use std::cout for writing on standard output. You can also use std::cerr for the standard error, and finally you can instantiate your own fstream if you want, for instance, to write on a file.

#include <iostream>
#include <fstream>

int main()
{
    std::fstream outfile ("output.txt", fstream::out);

    outfile << "Hello World" << std::endl;

    // Always close streams
    outfile.close();
}

As side note: i suggest not to export the std namespace (use namespace std) in your programs (see this faq)

ostream usage in C++

4 Answers4