Check if string has no characters

jaymoore_299

What is the best way to check whether a string has only whitespace characters?

I need a way to evaluate a string so that if it is either
"" or " " (has space characters only)
then it evaluates to false
"a" "0" "." will evaluate to true.

bradgrafelman

Well which is it... white space characters or just spaces? If it's the latter... what kind of spaces? Normal spaces (ASCII value 0x20) and/or non-breaking spaces (Unicode character U+00A0)?

jaymoore_299

Anything with whitespace characters should evaluate to false.

NogDog

I usually [man]trim/man all the form inputs first. Then you can just check if $var === "" (note the === operator as opposed to ==, so that 0 (zero) is not considered empty).

bradgrafelman

[man]trim/man will work for most cases... except for the non-breaking space character I talked about above. Many, many applications overlook this space character (I've found many bugs/exploits/loopholes/etc. using this character :p). For example, this code:

<?php
header('Content-Type: text/plain');
$str = "**************"; // these are non-breaking spaces, Unicode character U+00A0

echo '|' . trim($str) . "|\n";
echo '|' . preg_replace('/\s/', '', $str) . "|\n";

outputs:

|              |
||

(Note that in my code above, the vBulletin software replaces the Unicode characters with an asterisk.)

EDIT: Note that the above statement about trim() holds true for PHP 5.3.2 and prior. It's possible that PHP 6 (which is supposedly more Unicode-centric/-friendly/-aware) might be adjusted to look for this Unicode character as well.

jaymoore_299

That should work, thanks.

NogDog

$var = trim($var, " \t\n\r\0\x0B\xA0");

🙂