The reason it is doing that is the order in which PHP is processing your operators.
It processes !mb_strlen($string, 'utf-8') first, so if the length is non-zero that will return true.
It then evaluates true <= 30, which is always true...
So essentially the only case your statement will be false is if a zero length string is given...
See the other answers for how you should write the statement.
Answer from Jacob on Stack OverflowThe reason it is doing that is the order in which PHP is processing your operators.
It processes !mb_strlen($string, 'utf-8') first, so if the length is non-zero that will return true.
It then evaluates true <= 30, which is always true...
So essentially the only case your statement will be false is if a zero length string is given...
See the other answers for how you should write the statement.
Why don’t you write the code as you verbalized it?
mb_strlen($string, 'utf-8') > 30
The reason why your condition fails is because ! has a higher operator precedence than <=. So !mb_strlen($string, 'utf-8') is evaluated before it is compared to 30, i.e.:
(!mb_strlen($string, 'utf-8')) <= 30
And since any number except 0 evaluates to true when converted to boolean, the expression !mb_strlen($string, 'utf-8') is only true for an empty string. And as <= requires the first operand to be numeric, the boolean result of !mb_strlen($string, 'utf-8') is converted to integer where (int)true === 1 and (int)false === 0 and both is alway less than or equal to 30.
To make it short: you do not really know about the encoding (character set) used on the variables that are passed to your PHP script via GET or POST (especially GET is a problem here). By convention browsers POST forms to the server-side resource specified in the action-attribute using the page encoding which can be specified via an http-equiv-meta-tag (charset-meta-tag in HTML5) or via an HTTP header. Alternatively some browsers also respect the accept-charset-attribute on the form when chosing the correct encoding.
The encoding of GET parameters and the URL itself depends on the browser stettings and can therefore be controlled by the user. You should not rely on a specific encoding.
Generally you'll circumnavigate most encoding-related problems by consistently using UTF-8 for everything and by specifying the correct encoding in the HTTP-header (Content-Type: text/html; charset=UTF-8) - this will yield the correct encoding (UTF-8) in all the variables that are passed into your string (we're not talking about rouge scripts that deliberately try to mess with the encoding to allow for some attack vectors into your script). You also should not rely on non-ascii-characters in your GET parameters or in the URL (that's also a reason why SEO-friendly links remove those characters or substitute them).
If you made sure that UTF-8 is the only allowed character-set you can use mb_strlen($string, 'UTF-8') to check the length of a variable for example.
EDIT: (added some links)
Some things for you to read:
- The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)
- Handling UTF-8 with PHP
use mb_internal_encoding to know which encoding is currently set. If you application use a log of different encoding you have better to use mb_strlen.
Cheers