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After an error is detected, it can be handled in different ways. The web browser uses two ways: trying again, and terminating the program with an error message. If the user gave a zero-length web address, the program asks again.

If you want to terminate the program, this is a common code snippet:

if(result_of_something == 0)
  werror("Failed to open the file called '" +
         file_name + "'\n");

The call to exit will terminate the program. An argument greater than 0 to exit, or as a return value from main, means that the program failed in some way.

The built-in function werror prints a string on the standard error output (Stdio.stderr) instead of the normal standard output (Stdio.stdout). This has a higher chance of being seen by the user, since if you re-direct the output from a program, like this:

webbrowser.pike cod.ida.liu.se > output.txt

then the standard output will be printed to the file output.txt, but the standard error output will still be printed on the screen.