Why a function checking if a string is empty always returns true?

bgosalci_75168 0
Viewed 463724

I have a function isNotEmpty which returns true if the string is not empty and false if the string is empty. I've found out that it is not working if I pass an empty string through it. 

function isNotEmpty($input) 
{
    $strTemp = $input;
    $strTemp = trim($strTemp);

    if(strTemp != '') //Also tried this "if(strlen($strTemp) > 0)"
    {
         return true;
    }

    return false;
}

The validation of the string using isNotEmpty is done:

if(isNotEmpty($userinput['phoneNumber']))
{
    //validate the phone number
}
else
{
    echo "Phone number not entered<br/>";
}

If the string is empty the else doesn't execute, I don't understand why, can someone please shed some light on this please.

validation php string
14 Answers

Simple problem actually. Change:

if (strTemp != '')

to 

if ($strTemp != '')

Arguably you may also want to change it to:

if ($strTemp !== '')

since != '' will return true if you pass is numeric 0 and a few other cases due to PHP's automatic type conversion.

You should not use the built-in empty() function for this; see comments and the PHP type comparison tables.

cletus_183930

I always use a regular expression for checking for an empty string, dating back to CGI/Perl days, and also with Javascript, so why not with PHP as well, e.g. (albeit untested)

return preg_match('/\S/', $input);

Where \S represents any non-whitespace character

user_348060

In your if clause in the function, you're referring to a variable strTemp that doesn't exist. $strTemp does exist, though.

But PHP already has an empty() function available; why make your own?

if (empty($str))
    /* String is empty */
else
    /* Not empty */

From php.net:

Return Values

Returns FALSE if var has a non-empty and non-zero value.

The following things are considered to be empty:

* "" (an empty string)
* 0 (0 as an integer)
* "0" (0 as a string)
* NULL
* FALSE
* array() (an empty array)
* var $var; (a variable declared, but without a value in a class)

http://www.php.net/empty

Bj246rn_644950

PHP evaluates an empty string to false, so you can simply use:

if (trim($userinput['phoneNumber'])) {
  // validate the phone number
} else {
  echo "Phone number not entered<br/>";
}
user_181800

I needed to test for an empty field in PHP and used 

ctype_space($tempVariable)

which worked well for me.

user_114775970

You can simply cast to bool, dont forget to handle zero.

function isEmpty(string $string): bool {
    if($string === '0') {
        return false;
    }
    return !(bool)$string;
}

var_dump(isEmpty('')); // bool(true)
var_dump(isEmpty('foo')); // bool(false)
var_dump(isEmpty('0')); // bool(false)
user_48406610

I know this thread been pretty old but I just wanted to share one of my function. This function below can check for empty strings, string with maximum lengths, minimum lengths, or exact length. If you want to check for empty strings, just put $min_len and $max_len as 0.

function chk_str( $input, $min_len = null, $max_len = null ){

    if ( !is_int($min_len) && $min_len !== null ) throw new Exception('chk_str(): $min_len must be an integer or a null value.');
    if ( !is_int($max_len) && $max_len !== null ) throw new Exception('chk_str(): $max_len must be an integer or a null value.'); 

    if ( $min_len !== null && $max_len !== null ){
         if ( $min_len > $max_len ) throw new Exception('chk_str(): $min_len can\'t be larger than $max_len.');
    }

    if ( !is_string( $input ) ) {
        return false;
    } else {
        $output = true;
    }

    if ( $min_len !== null ){
        if ( strlen($input) < $min_len ) $output = false;
    }

    if ( $max_len !== null ){
        if ( strlen($input) > $max_len ) $output = false;
    }

    return $output;
}
user_74497060
Related