6.9. Returning Failure
Problem
You want to indicate failure from a function.
Solution
Return false
:
function lookup($name) { if (empty($name)) { return false; } ... } if (false !== lookup($name)) { /* act upon lookup */ }
Discussion
I
n PHP, non-true values aren’t
standardized and can easily cause errors. As a result,
it’s best if all your functions return the defined
false
keyword because this works best when
checking a logical value.
Other possibilities are ''
or 0
. However,
while all three evaluate to non-true inside an if
,
there’s actually a difference among them. Also,
sometimes a return value of 0
is a meaningful
result, but you still want to be able to also return failure.
For example, strpos( )
returns the location of the first substring
within a string. If the substring isn’t found,
strpos( )
returns false
. If it
is found, it returns an integer with the position. Therefore, to find
a substring position, you might write:
if (strpos($string, $substring)) { /* found it! */ }
However, if $substring
is found at the exact start
of $string
, the value returned is
0
. Unfortunately, inside the
if
, this evaluates to false
, so
the conditional is not executed. Here’s the correct
way to handle the return value of strpos( )
:
if (false !== strpos($string, $substring)) { /* found it! */ }
Also, false
is always guaranteed to be
false — in the current version of PHP and forever more. Other
values may not guarantee this. For example, in PHP 3,
empty('0')
was true
, but it
changed to false
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