In PHP, if 0==false is true, and false==false is true, how to test for false?

I am especially interested in testing the return value of preg_match开发者_Go百科, which can be 1, 0, or false.

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$val === false;

Example:

0 === false; // returns false
false === false; // returns true

Use triple equals operator/strict comparison

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Use === type comparison. Check the manual: http://www.php.net/manual/en/language.operators.comparison.php

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$num === 0; //is true if $num is 0 and is an integer
$num === 0; //is false if $num is 0 and is a string

The === checks for type as well as equality

so:

 0 === false; //will return false
 false === false; //will return true

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preg_match() and preg_match_all() return the number of matches found, or false in case of an error. However this means it will return 0 if no matches are found so testing explicitly for false and then trying to loop through an empty set will still be problematic.

I usually test for false, then test again for match count before looping results. Something to the effect of:

$match = preg_match_all($pattern, $subject, $matches);

if($match !== false)
{
    if(count($matches) > 0)
    {
        foreach($matches as $k=>$v)
        {
            ...
        }
    }
    else
    {
        user_error('Sorry, no matches found');
    }
}
else
{
    die('Match error');
}

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Use the not operator ! to check for false: (! 0 === false) is always false.