=over 4
-=item size
+=item fsize
Size_t fsize;
=back
+=head2 Implementing PerlIO Layers
+
+If you are creating a PerlIO layer, you may want to be lazy, in other
+words, implement only the methods that interest you. The other methods
+you can either replace with the "blank" methods
+
+ PerlIOBase_noop_ok
+ PerlIOBase_noop_fail
+
+(which do nothing, and return zero and -1, respectively) or for
+certain methods you may assume a default behaviour by using a NULL
+method. The Open method looks for help in the 'parent' layer.
+The following table summarizes the behaviour:
+
+ method behaviour with NULL
+
+ Clearerr PerlIOBase_clearerr
+ Close PerlIOBase_close
+ Dup PerlIOBase_dup
+ Eof PerlIOBase_eof
+ Error PerlIOBase_error
+ Fileno PerlIOBase_fileno
+ Fill FAILURE
+ Flush SUCCESS
+ Getarg SUCCESS
+ Get_base FAILURE
+ Get_bufsiz FAILURE
+ Get_cnt FAILURE
+ Get_ptr FAILURE
+ Open INHERITED
+ Popped SUCCESS
+ Pushed SUCCESS
+ Read PerlIOBase_read
+ Seek FAILURE
+ Set_cnt FAILURE
+ Set_ptrcnt FAILURE
+ Setlinebuf PerlIOBase_setlinebuf
+ Tell FAILURE
+ Unread PerlIOBase_unread
+ Write FAILURE
+
+ FAILURE Set errno (to EINVAL in UNIXish, to LIB$_INVARG in VMS) and
+ return -1 (for numeric return values) or NULL (for pointers)
+ INHERITED Inherited from the layer below
+ SUCCESS Return 0 (for numeric return values) or a pointer
=head2 Core Layers
find it. It is an example of a layer which takes an argument as it is
called thus:
- open($fh,"<:encoding(iso-8859-7)",$pathname)
+ open( $fh, "<:encoding(iso-8859-7)", $pathname );
-=item ":Scalar"
+=item ":scalar"
-Provides support for
+Provides support for reading data from and writing data to a scalar.
- open($fh,"...",\$scalar)
+ open( $fh, "+<:scalar", \$scalar );
When a handle is so opened, then reads get bytes from the string value
of I<$scalar>, and writes change the value. In both cases the position
in I<$scalar> starts as zero but can be altered via C<seek>, and
determined via C<tell>.
-=item ":Via"
+Please note that this layer is implied when calling open() thus:
+
+ open( $fh, "+<", \$scalar );
+
+=item ":via"
Provided to allow layers to be implemented as Perl code. For instance:
- use MIME::QuotedPrint;
- open(my $fh, ">Via(MIME::QuotedPrint)", "qp");
+ use PerlIO::via::StripHTML;
+ open( my $fh, "<:via(StripHTML)", "index.html" );
-See L<PerlIO::Via> for details.
+See L<PerlIO::via> for details.
=back
=back
=cut
-
-
-