Thread: cout, cerr

What is the difference between them? (if any)

Here is a good page to answer that.

http://www.cs.ust.hk/~martin/01Sprin...n_iostream.htm

cout is an input stream?

I gues cin is an output stream then?

hmm...

cerr and cout are both for output.
cerr is especialy for error messages.
I knew it even before opening this thread.

Then what was the point of the thread?

No, what I don't know is the difference in their functionality. Why there are different objects for normal text output and error output.

Originally Posted by siavoshkc

No, what I don't know is the difference in their functionality. Why there are different objects for normal text output and error output.

I thought Sly hit that already.

Originally Posted by SlyMaelstrom

Here is a good page to answer that.

http://www.cs.ust.hk/~martin/01Sprin...n_iostream.htm

Did you follow this link?

The difference between cout and cerr is illustrated clearly during output redirection (forget about it? Take a look here!). Only data output by cout are redirected to the file. Data output by cerr are still displayed in the terminal. This is usually what we want, because error messages should not mix with normal output which are redirected to a file in this example.

I read that and concluded that it makes no difference in output to screen. And if we have a fstream object then cerr will output the text to screen instead of file, am I right?

How about an example?

Code:

#include <iostream>
using std::cout;
using std::cerr;

int main()
{
   for ( int i = 0; i < 10; ++i )
   {
      cout << "cout: i = " << i << '\n';
      if ( i & 1 )
      {
         cerr << "cerr: i = " << i << '\n';
      }
   }
   return 0;
}

Running it without redirection:

Code:

C:\Test\GnuC>Cpp\myapp.exe
cerr: i = 1
cerr: i = 3
cerr: i = 5
cerr: i = 7
cerr: i = 9
cout: i = 0
cout: i = 1
cout: i = 2
cout: i = 3
cout: i = 4
cout: i = 5
cout: i = 6
cout: i = 7
cout: i = 8
cout: i = 9

Redirecting stdout:

Code:

C:\Test\GnuC>Cpp\myapp.exe > output.txt
cerr: i = 1
cerr: i = 3
cerr: i = 5
cerr: i = 7
cerr: i = 9

The contents of output.txt:

Code:

cout: i = 0
cout: i = 1
cout: i = 2
cout: i = 3
cout: i = 4
cout: i = 5
cout: i = 6
cout: i = 7
cout: i = 8
cout: i = 9

Redirecting stderr:

Code:

C:\Test\GnuC>Cpp\myapp.exe 2> errors.txt
cout: i = 0
cout: i = 1
cout: i = 2
cout: i = 3
cout: i = 4
cout: i = 5
cout: i = 6
cout: i = 7
cout: i = 8
cout: i = 9

The contents of errors.txt:

Code:

cerr: i = 1
cerr: i = 3
cerr: i = 5
cerr: i = 7
cerr: i = 9

Aha, I didn't know about redirection and when I pressed the link(in sly's link) it was about makefile!!