MySQL in a Nutshell, 2nd Edition

Name

set_err()

Synopsis

$handle->set_err($err, $errstr[, $state[, $method[, $return_value]]])

This function sets the values for err, errstr, and state for the handle. The method (e.g., RaiseError) can be changed as well. It returns undef unless a different return value is given as the fifth argument to this method. You can use this manually to return an error message to a user. Here is an example:

...
my $book_id = shift;
my $books = &get_data_ref($book_id) 
   or print "Error: " . DBI->err . DBI->errstr;
...

sub get_data_ref {
  my $book_id = shift;

  if($book_id =~ m/\D/g) {
     return $dbh->DBI::set_err(500, "\nYou entered '$book_id'.\nBad Book 
        ID!");
     last;
  }
  ...
}

Notice in the subroutine that if it is given a book identifier that contains any nonnumeric characters, it does not proceed and instead returns the error as set by set_err. The line of code at the top of the excerpt that calls the subroutine will display the results if true, or display the error number and string. Here are the results of the program when a user enters a book ID that contains a letter:

Error: 500
You entered '100g'?
Bad Book ID!