PHP常量不存在：注意

Question

I'd like to use constants as config variables within my PHP applications, only when a constant doesn't exist (for whatever reason) it throws me a notice but I'd like that to be an error (or exception), just like when I try to echo a not existing variable.

Is that possible without using a separate function for getting constant values, something like this:

echo $non_existing_variable; // Error
echo NON_EXISTING_CONSTANT; // Now also an error

Been searching around a bit but couldn't find anything.

Seems kind of logical to me, when I try to use a variable that doesn't exist code execution quits immediately and throws an error, why isn't that with constants?

Answer 1

I'd suggest using defined with it you should be able to do something like

if (defined('CONSTANT')) {
    echo CONSTANT;
} else {
    throw new Exception('Undefined Constant.');
}

Edit:

The alternative to using this method as I stated in the comment below is to use a custom error handler, by using set_error_handler you should be able to catch the notice and take an action.