ITEC 325 2011spring ibarland

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error-checking-misc
input validation
functions; miscellania

• When you find an error: perhaps set a global flag, and print a specific error message. Javascript: you can alert, or you can insert some error text. Trade-offs?

  To avoid repeated code: Use functions to validate. (One argument will be a string to use in the error output.)

• Javascript: onsubmit's code should return false, if an error. This will cause the script to not actually submit the form.

• Principle: Make your javacode and php validation code look as similar as possible: same function-names, same approach, same regular expressions, etc.. This way, when you edit/debug one side it's easy to find&fix the corresponding code on the other side.

• If you validate input on both client-side and server-side, how can you tell if it's working?
  Use functions, and (on client) a global DISABLE_VALIDATION; end each error-checking function in return DISABLE_VALIDATION || ....

  (You might also want to print a warning to the html, when validation is turned off so you don't accidentally release them (or turn them in as homework).

• A case study in abstracting javascript: A sequence of Javascript programs, which all do the same thing, ranging in quality from C to A+: lect00—intro
• For hw01:
  • You can use javascript alert (you don't need to have a red message appear on the page).
  • You do need to make sure the javascripts onsubmit code returns false if there is an error (even if you're using alert.
  • Having separate function for “validPlainText” which is separate from the code which creates the error message is good: that lets you increase the similarity between your php and javascript scripts (since they inherently do different things upon finding the error) and lets you re-use that javascript/php code more easily in the future.
  • Use style sheet, for the display attributes of an error message (if you don't use alert).

• Note: How to ssh w/o always typing password: storing a public key in .ssh/.

PHP regular expressions

      echo preg_match( '/row/', 'How now, brown cow?' );
      echo preg_match( '/r.w/', 'How now, brown cow?' );
      echo preg_match( '/n[oe]w/', 'How now, brown cow?' );
      echo preg_match( '/rows?/', 'How now, brown cow?' );
      echo preg_match_all( '/ow/', 'How now, brown cow?' );
      echo preg_match_all( '/rows?/', '\"How now, brown cow?\", he crows.' );

      echo preg_match( '/[0-9]*/', '00047' );
      echo preg_match( '/\\d*/',   '00047' );
      echo preg_match( '/[0-9]+/', '00047' );
    

Atomic regexps

• ^ : matches start-of-string
• $ : matches end-of-string
• . : matches any one character
• Most characters match themselves (e.g. 'b'); you can escape special characters with backslash.
• Character classes:
  • [[:space:]]
  • [[:alpha:]]
  • [[:upper:]]
  • [[:lower:]]
  • [[:digit:]] matches '0'..'9'
  • [[:punct:]] One of: “.”   “!”   “?”   “:”   “;”   “?” “"”   “'”
  • […] — build your own character set, e.g. [aeiou] matches any one lower-case vowel.
    Use ^ just inside the [ to negate the set. (Note that this overrides the beginning-of-string meaning of ^; it's clear from context).
  Each of these match one character; they are often used in conjunction with * and + below.

Compound regexps

• * — 0 or more occurrences
• + — 1 or more occurrences
• ? — 0 or 1 occurrence
• {…} — you specify how many repetitions (not very common)

• preg_match($pat,$target) (also, note: preg_match_all — not as common, but it motivates why preg_match's output is 0,1 and not a raw boolean).
• preg_replace($pat,$target,$new)
• split($pat,$target) Returns an array (indexed numerically from 0)

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©2010, Ian Barland, Radford University Last modified 2011.Feb.11 (Fri)

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