PHP: "Notice: Undefined variable" and "Notice: Undefined index" -

PHP: "Notice: Undefined variable" and "Notice: Undefined index" -

i running php script, , maintain getting errors like:

undefined variable: user_location in c:\wamp\www\mypath\index.php on line 12

line 12 looks this:

$greeting = "hello, ".$user_name." ".$user_location;

what these errors mean?

why appear of sudden? used utilize script years , i've never had problem.

what need prepare them?

is there quick fix?

this general reference question people link duplicate, instead of having explain issue on , on again. sense necessary because real-world answers on issue specific.

related meta discussion:

what can done repetitive questions? do “reference questions” create sense?

from vast wisdom of php manual:

relying on default value of uninitialized variable problematic in case of including 1 file uses same variable name. major security risk register_globals turned on. e_notice level error issued in case of working uninitialized variables, not in case of appending elements uninitialized array. isset() language build can used observe if variable has been initialized.

some explanations:

although php not require variable declaration, recommend in order avoid security vulnerabilities or bugs 1 forget give value variable utilize later in script. php in case of undeclared variables issue low level error, e_notice, 1 not reported default, manual advises allow during development.

ways deal issue:

recommended: declare variables. or utilize isset() check if declared before referencing them, in: $value = isset($_post['value']) ? $_post['value'] : '';.

use empty(), no warning generated if variable not exist. it's equivalent !isset($var) || $var == false. e.g.

echo "hello " . (!empty($user) ? $user : "");

set custom error handler e_notice , redirect messages away standard output (maybe log file). set_error_handler('myhandlerforminorerrors', e_notice | e_strict).

disable e_notice reporting. quick way exclude e_notice error_reporting( error_reporting() & ~e_notice ).

suppress error @ operator.

note: it's recommended implement point 1.

related:

notice: undefined variable notice: undefined index

php undefined-index