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PHP Lesson 1: TRUE and FALSE in PHP world

PHP is a truly wonderful language. Type safety is a non existent concept, yet the absence of it also allows you to perform wonderful hacks. In light of this a miniature lesson in PHP: what constitutes TRUE in PHP, and what FALSE? I'll answer this by answering what constitutes FALSE: everything else (and I literally mean everything else) constitutes TRUE.

So why is this important? Many coders use code constructs like this:
$value = some_function(); if ($value) do_something_else();


If the
some_function
function returns a value of type
bool
, then there is really no question: if
true
is returned,
do_something_else
will be executed, if
false
is returned it won't. But... what if an array is returned? A floating point value? A string? An empty string? An object? NULL? These values will all in some way be converted to a boolean value:
true
or
false
. The list below indicates what values in PHP are converted to
false
. As said, all other possible values not listed here will convert to
true
.

  • false
    (type
    bool
    )
  • 0
    (type
    int
    , variations with more zero's as well)
  • 0.0
    (type
    float
    , variations with more zero's at either side of the dot as well)
  • null
    (the constant)
  • ""
    (an empty string)
  • "0"
    (a string containing the digit 0)
  • array()
    (an empty array)


To test the above theory, try to execute the following:

<?php foreach (array( false, 0, 0.0, null, "", "0", array() ) as $value) if ($value) echo "Oops, foddie was wrong";


Luckily for me, this will produce no output at all.... (at least in PHP 5 ;-))


1 comment(s)

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On Wed 20-07-2011 10:28 john wrote: thks,foddex,your words make me think more about php.
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