note 29273 modified in language.variables.scope by danbrown

It's possible to use a variable variable when specifying a variable as global in a function. That way your function can decide what global variable to access in run-time. <?php function func($varname) { global $$varname; echo $$varname; } $hello = "hello world!"; func("hello"); ?> This will print "hello world!", and is roughly the same as passing by reference, in the case when the variable you want to pass is global. The advantage over references is that they can't have default parameters. With the method above, you can do the following. <?php function func($varname = FALSE) { if ($varname === FALSE) echo "No variable."; else { global $$varname; echo $$varname; } } $hello = "hello world!"; func("hello"); // prints "hello world!" func(); // prints "No variable." ?> --was-- It's possible to use a variable variable when specifying a variable as global in a function. That way your function can decide what global variable to access in run-time. function func($varname) { global $$varname; echo $$varname; } $hello = "hello world!"; func("hello"); This will print "hello world!", and is roughly the same as passing by reference, in the case when the variable you want to pass is global. The advantage over references is that they can't have default parameters. With the method above, you can do the following. function func($varname = FALSE) { if ($varname === FALSE) echo "No variable."; else { global $$varname; echo $$varname; } } $hello = "hello world!"; func("hello"); // prints "hello world!" func(); // prints "No variable." http://php.net/manual/en/language.variables.scope.php