PHP does not issue a warning for undefined variables

Please correct me if I am wrong. From what I gather, PHP should issue a warning for th开发者_如何学JAVAis but doesn't. I am using PHP 5.2.17. How can I fix this? I am assuming this is set somewhere in php.ini?

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Check the docs for error reporting. I believe if you enable E_NOTICE you'll see warnings for undefined variables. You can read up on all the error reporting constants here.

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Probably error reporting is off.

error_reporting(-1);

Or, you are using a variable in a way that it does not have to be declared.