The include_once() statement includes and evaluates
the specified file during the execution of the script.
This is a behavior similar to the include() statement,
with the only difference being that if the code from a file has already
been included, it will not be included again. As the name suggests,
it will be included just once.
include_once() should be used in cases where
the same file might be included and evaluated more than once during a
particular execution of a script, and you want to be sure that it is
included exactly once to avoid problems with function redefinitions,
variable value reassignments, etc.
For more examples on using require_once() and
include_once(), look at the
PEAR code included in the latest
PHP source code distributions.
See also include(),
require(), require_once(),
get_required_files(),
get_included_files(), readfile(),
and virtual().
