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 important difference that if the code from a file has already
been included, it will not be included again.
As mentioned in the require_once() description, the
include_once() should be used in the cases in which
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: require(),
include(), require_once(),
get_required_files(),
get_included_files(), readfile(),
and virtual().
