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
.
See
also
:
require(
)
,
include(
)
,
require_once(
)
,
get_required_files(
)
,
get_included_files(
)
,
readfile(
)
,
and
virtual(
)
.