Registers the function named by function to be executed when script processing is complete.
Multiple calls to register_shutdown_function() can be made, and each will be called in the same order as they were registered. If you call exit() within one registered shutdown function, processing will stop completely and no other registered shutdown functions will be called.
In PHP 4.0.6 and earlier under Apache, the registered shutdown functions are called after the request has been completed (including sending any output buffers), so it is not possible to send output to the browser using echo() or print(), or retrieve the contents of any output buffers using ob_get_contents(). Since PHP 4.1, the shutdown functions are called as the part of the request so that it's possible to send the output from them. There is currently no way to process the data with output buffering functions in the shutdown function. Shutdown function is called after closing all opened output buffers thus, for example, its output will not be compressed if zlib.output_compression is enabled.
As of PHP 4, it is possible to pass parameters to the shutdown function by passing additional parameters to register_shutdown_function().
Typically undefined functions cause fatal errors in PHP, but when the
function called with
register_shutdown_function() is undefined, an error
E_WARNING is generated instead. Also,
for reasons internal to PHP, this error will refer to
Unknown at line #0.
Working directory of the script can change inside the shutdown function under some web servers, e.g. Apache.
Shutdown function is called during the script shutdown so headers are always already sent.