This code is part of a websocket server:
$msgArray = json_decode($msg);
if ($msgArray->sciID) {
echo "Has sciID";
}
It will either be receiving a json string like {"sciID":67812343} or a completely different json string with no sciID such as {"something":"else"}.
When the server receives the later, it echos out: Notice: Undefined property: stdClass::$sciID in /path/to/file.php on line 10
What is the correct code to check if $msgArray->sciID exists?
Use isset as a general purpose check (you could also use property_exists since you're dealing with an object):
if (isset($msgArray->sciID)) {
echo "Has sciID";
}
isset() and empty() a non-existant variable and a variable set to NULL are treated the same. Only property_exists and ReflectionObject will tell the difference.
In case isset() or property_exists() doesn't work, we can use array_key_exists()
if (array_key_exists("key", $array)) {
echo "Has key";
}
json_decode($str, true) to use array_key_existsI've always done isset() but I've recently changed to !empty() and empty because one of my friends suggested it.
php -r 'class A {} $a = new A; var_dump(isset($a->b), empty($a->b));' returns TRUE and FALSE respectively), however I'm not sure why - probably because an undefined property doesn't equate to NULL or FALSE or anything else considered 'empty' as trying to access it throws a notice. Personally I like to distinguish between what I'm checking - if I'm checking for 0, null or an empty string I use ==0, is_null and strlen because of the issue above.The isset() function checks if a variable is set and is not null, which is really stupid, given its name. If you only want to know if a variable is set, use the following function:
function is_set( & $variable ) {
if ( isset( $variable ) and ! is_null( $variable ) )
return true;
else
return false;
}
This function will return true exactly when the variable is not set, and false otherwise. The '&' next to the argument is important, because it tells PHP to pass a reference to the variable, and not the value of the variable, thus avoiding a "Notice: Undefined variable" when the variable is not set.
