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Using stderr for error Messages

  • fprintf allows you to specify stream to print to
  • For example: 

    fprintf(stderr, "error: can not open %s\n", argv[1]);

  • printf actually just calls fprintf specifying stdout 

    fprintf(stdout, ...);

  • Best if error messages written to stderr, so users sees them even if stdout is directed to a file.
  • Common for stderr to be redirected separately to a log file for system programs.