Is it safe to use $_ prefix on custom PHP variables

Question

I know it's possible to set custom PHP variables using the $_ prefix, however I am unsure if it is safe to do this? I wouldn't be setting many, nor would I be overwriting pre-set variables like $_SERVER or $_COOKIE. Should I just avoid doing it at all?

Answer 1

It is completely safe to initialize variables that start with $_ as long as you don't override any of the superglobals (that you need).

However, the $_ prefix on variables indicates that they are superglobals or have some other kind of magic behavior, so to do so on "normal" variables would be nonstandard.

Answer 2

This notation is normally used inside classes to indicate private or protected members (either properties or methods). In this situation it is completely safe.

Note, the php manual has a caution on using double underscore to prefix methods, as this notation is reserved for "magic" methods. This caution does not apply to the single underscore prefix.