clog

Library:  Input/output

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A predefined stream that controls output to a stream buffer associated with the object stderr declared in <cstdio>

#include <iostream>

namespace std {
  extern ostream clog;
}

The object clog controls output to a stream buffer associated with the object stderr declared in <cstdio>. The difference between clog and cerr is that clog is buffered but cerr is not. Therefore, commands like clog << "ERROR !!"; and fprintf(stderr,"ERROR !!"); are not synchronized.

The formatting is done through member functions or manipulators. See cout or basic_ostream for details.

clog can be used to redirect some of the errors to another recipient. For example, you might want to redirect them to a file named my_err, as in:

ofstream out("my_err");
if ( out )
  clog.rdbuf(out.rdbuf());

else

  cerr << "Error while opening the file" << endl;

Then when you are doing something like:

clog << "error number x"; 

the error message is output to the file my_err. Obviously, you can use the same scheme to redirect clog to other devices.

basic_ostream, basic_iostream, basic_filebuf, cout, cin, cerr, wcin, wcout, wcerr, wclog, ios_base, basic_ios

ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 27.3.1