sin(x)
double x
-When using parameters with C pointer types, as in
+Optionally, one can merge the description of types and the list of
+argument names, rewriting this as
- double string_to_double(char *s);
+ double
+ sin(double x)
+
+This makes this XSUB look similar to an ANSI C declaration. An optional
+semicolon is allowed after the argument list, as in
+
+ double
+ sin(double x);
+
+Parameters with C pointer types can have different semantic: C functions
+with similar declarations
-there may be two ways to describe this argument to B<xsubpp>:
+ bool string_looks_as_a_number(char *s);
+ bool make_char_uppercase(char *c);
+
+are used in absolutely incompatible manner. Parameters to these functions
+could be described B<xsubpp> like this:
char * s
- char &s
+ char &c
Both these XS declarations correspond to the C<char*> C type, but they have
-different semantics. It is convenient to think that the indirection operator
+different semantics, see L<"The & Unary Operator">.
+
+It is convenient to think that the indirection operator
C<*> should be considered as a part of the type and the address operator C<&>
-should be considered part of the variable. See L<"The Typemap"> and
-L<"The & Unary Operator"> for more info about handling qualifiers and unary
-operators in C types.
+should be considered part of the variable. See L<"The Typemap">
+for more info about handling qualifiers and unary operators in C types.
The function name and the return type must be placed on
separate lines and should be flush left-adjusted.
double x sin(x)
double x
-The function body may be indented or left-adjusted. The following example
+The rest of the function description may be indented or left-adjusted. The following example
shows a function with its body left-adjusted. Most examples in this
document will indent the body for better readability.
remainder of the OUTPUT section. See L<perlguts> for more details
about 'set' magic.
+=head2 The NO_OUTPUT Keyword
+
+The NO_OUTPUT can be placed as the first token of the XSUB. This keyword
+indicates that while the C subroutine we provide an interface to has
+a non-C<void> return type, the return value of this C subroutine should not
+be returned from the generated Perl subroutine.
+
+With this keyword present L<The RETVAL Variable> is created, and in the
+generated call to the subroutine this variable is assigned to, but the value
+of this variable is not going to be used in the auto-generated code.
+
+This keyword makes sense only if C<RETVAL> is going to be accessed by the
+user-supplied code. It is especially useful to make a function interface
+more Perl-like, especially when the C return value is just an error condition
+indicator. For example,
+
+ NO_OUTPUT int
+ delete_file(char *name)
+ POST_CALL:
+ if (RETVAL != 0)
+ croak("Error %d while deleting file '%s'", RETVAL, name);
+
+Here the generated XS function returns nothing on success, and will die()
+with a meaningful error message on error.
+
=head2 The CODE: Keyword
This keyword is used in more complicated XSUBs which require
C<h = host> is not performed too early. Otherwise one would need to have the
assignment C<h = host> in a CODE: or INIT: section.)
+=head2 The IN/OUTLIST/IN_OUTLIST Keywords
+
+In the list of parameters for an XSUB, one can precede parameter names
+by the C<IN>/C<OUTLIST>/C<IN_OUTLIST> keywords. C<IN> keyword is a default,
+the other two keywords indicate how the Perl interface should differ from
+the C interface.
+
+Parameters preceded by C<OUTLIST>/C<IN_OUTLIST> keywords are considered to
+be used by the C subroutine I<via pointers>. C<OUTLIST> keyword indicates
+that the C subroutine does not inspect the memory pointed by this parameter,
+but will write through this pointer to provide additional return values.
+Such parameters do not appear in the usage signature of the generated Perl
+function.
+
+Parameters preceded by C<IN_OUTLIST> I<do> appear as parameters to the
+Perl function. These parameters are converted to the corresponding C type,
+then pointers to these data are given as arguments to the C function. It
+is expected that the C function will write through these pointers
+
+The return list of the generated Perl function consists of the C return value
+from the function (unless the XSUB is of C<void> return type or
+C<The NO_INIT Keyword> was used) followed by all the C<OUTLIST>
+and C<IN_OUTLIST> parameters (in the order of appearence). Say, an XSUB
+
+ void
+ day_month(OUTLIST day, IN unix_time, OUTLIST month)
+ int day
+ int unix_time
+ int month
+
+should be used from Perl as
+
+ my ($day, $month) = day_month(time);
+
+The C signature of the corresponding function should be
+
+ void day_month(int *day, int unix_time, int *month);
+
+The C<in>/C<OUTLIST>/C<IN_OUTLIST> keywords can be mixed with ANSI-style
+declarations, as in
+
+ void
+ day_month(OUTLIST int day, int unix_time, OUTLIST int month)
+
+(here the optional C<IN> keyword is omitted).
+
+The C<IN_OUTLIST> parameters are somewhat similar to parameters introduced
+with L<The & Unary Operator> and put into the C<OUTPUT:> section (see
+L<The OUTPUT: Keyword>). Say, the same C function can be interfaced with as
+
+ void
+ day_month(day, unix_time, month)
+ int &day = NO_INIT
+ int unix_time
+ int &month = NO_INIT
+ OUTPUT:
+ day
+ month
+
+However, the generated Perl function is called in very C-ish style:
+
+ my ($day, $month);
+ day_month($day, time, $month);
+
=head2 Variable-length Parameter Lists
XSUBs can have variable-length parameter lists by specifying an ellipsis
OUTPUT:
RETVAL
-In fact, one can put this check into a CLEANUP: section as well. Together
+In fact, one can put this check into a POST_CALL: section as well. Together
with PREINIT: simplifications, this leads to:
int
rpcb_gettime(host)
char *host
time_t timep;
- CLEANUP:
+ POST_CALL:
if (RETVAL == 0)
XSRETURN_UNDEF;
code specified for the cleanup block will be added as the last statements
in the XSUB.
+=head2 The POST_CALL: Keyword
+
+This keyword can be used when an XSUB requires special procedures
+executed after the C subroutine call is performed. When the POST_CALL:
+keyword is used it must precede OUTPUT: and CLEANUP: blocks which are
+present in the XSUB.
+
+The POST_CALL: block does not make a lot of sense when the C subroutine
+call is supplied by user by providing either CODE: or PPCODE: section.
+
=head2 The BOOT: Keyword
The BOOT: keyword is used to add code to the extension's bootstrap
=head2 Inserting Comments and C Preprocessor Directives
C preprocessor directives are allowed within BOOT:, PREINIT: INIT:,
-CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions.
+CODE:, PPCODE:, POST_CALL:, and CLEANUP: blocks, as well as outside the functions.
Comments are allowed anywhere after the MODULE keyword. The compiler
will pass the preprocessor directives through untouched and will remove
the commented lines.
candidates to return undef or an empty list in case of failure. If the
failure may be detected without a call to the C function, you may want to use
an INIT: section to report the failure. For failures detectable after the C
-function returns one may want to use a CLEANUP: section to process the
+function returns one may want to use a POST_CALL: section to process the
failure. In more complicated cases use CODE: or PPCODE: sections.
If many functions use the same failure indication based on the return value,
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