Once again I am struck by how true it is, that a good programmer should always follow up on warnings.

I'm writing a DBI program with a CGI interface. The program reads information from the database, performs some transformations, and puts the result into an HTML table. Easy.

But my database has a number of NULL values. This didn't cause any problems in the HTML output, it just made Perl generate a hundreds of annoying warnings about the "use of an uninitialized value". (When using "warnings", of course.) I'll admit that I always used to hate this warning -- after all, I didn't really care if the values were defined or not, as long as the output looked okay.

I initially intended to turn off the warnings, at least in a small block around my string-handling code. But there was this little nagging voice in my head that said, "Make your program run clean under 'use warnings' and 'use strict'". I'm pretty sure that I got this voice from Perl Monks.

And so I spent thirty minutes finding all of the places where the data could possibly be NULL, and I made sure they were defined, like this: 

$string = "" unless defined($string);

[download]
This got rid of most of the warnings, but there were more. Whoops, I missed a few NULLs. Thirty minutes later I was sure that I had tracked them all down, so I ran the program again. Now, my hundreds of warnings were down to about five.

So I spent another thirty minutes trying to find a place in my code where I could still be getting undefined values. And what did I find? A very real problem with my database. There were NULLS in fields where there shouldn't have been -- where I was absolutely positive that there weren't any. I hadn't even thought to double-check it before.

I've fixed my database, and the program runs clean now. And I am very glad that I didn't turn off warnings, even for one seemingly innocent line of code.

buckaduck

In reply to Always Follow Up on Warnings by buckaduck

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.