Recommended: Declare your variables, for example when you try to append a string to an undefined variable. What PHP does in the case of undeclared variables is issue a very low level error, E_NOTICE, one that is not even reported by default, but the Manual advises to allow during development. Test the above snippet in the online PHP editorĪlthough PHP does not require a variable declaration, it does recommend it in order to avoid some security vulnerabilities or bugs where one would forget to give a value to a variable that will be used later in the script. This means that you could use only empty() to determine if the variable is set, and in addition it checks the variable against the following, 0, 0.0, "", "0", null, false or. That meansĮmpty() is essentially the concise equivalent to !isset($var) || $var No warning is generated if the variable does not exist. Additionally and more ideal is the solution of empty() since it does not generate a warning or error message if the variable is not initialized. isset() language construct can be used to detect if a variable has been already initialized. E_NOTICE level error is issued in case of working with uninitialized variables, however not in the case of appending elements to the uninitialized array. It is also a major security risk with register_globals turned on. Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name.
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