PERLXSTYPEMAP(1) Perl Programmers Reference Guide PERLXSTYPEMAP(1) #
PERLXSTYPEMAP(1) Perl Programmers Reference Guide PERLXSTYPEMAP(1)
NNAAMMEE #
perlxstypemap - Perl XS C/Perl type mapping
DDEESSCCRRIIPPTTIIOONN #
The more you think about interfacing between two languages, the more
you'll realize that the majority of programmer effort has to go into
converting between the data structures that are native to either of the
languages involved. This trumps other matter such as differing calling
conventions because the problem space is so much greater. There are
simply more ways to shove data into memory than there are ways to
implement a function call.
Perl XS' attempt at a solution to this is the concept of typemaps. At an
abstract level, a Perl XS typemap is nothing but a recipe for converting
from a certain Perl data structure to a certain C data structure and vice
versa. Since there can be C types that are sufficiently similar to one
another to warrant converting with the same logic, XS typemaps are
represented by a unique identifier, henceforth called an XXSS ttyyppee in this
document. You can then tell the XS compiler that multiple C types are to
be mapped with the same XS typemap.
In your XS code, when you define an argument with a C type or when you
are using a "CODE:" and an "OUTPUT:" section together with a C return
type of your XSUB, it'll be the typemapping mechanism that makes this
easy.
AAnnaattoommyy ooff aa ttyyppeemmaapp In more practical terms, the typemap is a collection of code fragments which are used by the xxssuubbpppp compiler to map C function parameters and values to Perl values. The typemap file may consist of three sections labelled “TYPEMAP”, “INPUT”, and “OUTPUT”. An unlabelled initial section is assumed to be a “TYPEMAP” section. The INPUT section tells the compiler how to translate Perl values into variables of certain C types. The OUTPUT section tells the compiler how to translate the values from certain C types into values Perl can understand. The TYPEMAP section tells the compiler which of the INPUT and OUTPUT code fragments should be used to map a given C type to a Perl value. The section labels “TYPEMAP”, “INPUT”, or “OUTPUT” must begin in the first column on a line by themselves, and must be in uppercase.
Each type of section can appear an arbitrary number of times and does not
have to appear at all. For example, a typemap may commonly lack "INPUT"
and "OUTPUT" sections if all it needs to do is associate additional C
types with core XS types like T_PTROBJ. Lines that start with a hash "#"
are considered comments and ignored in the "TYPEMAP" section, but are
considered significant in "INPUT" and "OUTPUT". Blank lines are generally
ignored.
Traditionally, typemaps needed to be written to a separate file,
conventionally called "typemap" in a CPAN distribution. With
ExtUtils::ParseXS (the XS compiler) version 3.12 or better which comes
with perl 5.16, typemaps can also be embedded directly into XS code using
a HERE-doc like syntax:
TYPEMAP: «HERE #
...
HERE #
where "HERE" can be replaced by other identifiers like with normal Perl
HERE-docs. All details below about the typemap textual format remain
valid.
The "TYPEMAP" section should contain one pair of C type and XS type per
line as follows. An example from the core typemap file:
TYPEMAP #
# all variants of char* is handled by the T_PV typemap
char * T_PV
const char * T_PV
unsigned char * T_PV
...
The "INPUT" and "OUTPUT" sections have identical formats, that is, each
unindented line starts a new in- or output map respectively. A new in-
or output map must start with the name of the XS type to map on a line by
itself, followed by the code that implements it indented on the following
lines. Example:
INPUT #
T_PV #
$var = ($type)SvPV_nolen($arg)
T_PTR #
$var = INT2PTR($type,SvIV($arg))
We'll get to the meaning of those Perlish-looking variables in a little
bit.
Finally, here's an example of the full typemap file for mapping C strings
of the "char *" type to Perl scalars/strings:
TYPEMAP #
char * T_PV
INPUT #
T_PV #
$var = ($type)SvPV_nolen($arg)
OUTPUT #
T_PV #
sv_setpv((SV*)$arg, $var);
Here's a more complicated example: suppose that you wanted "struct
netconfig" to be blessed into the class "Net::Config". One way to do
this is to use underscores (_) to separate package names, as follows:
typedef struct netconfig * Net_Config;
And then provide a typemap entry "T_PTROBJ_SPECIAL" that maps underscores
to double-colons (::), and declare "Net_Config" to be of that type:
TYPEMAP #
Net_Config T_PTROBJ_SPECIAL
INPUT #
T_PTROBJ_SPECIAL #
if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")){
IV tmp = SvIV((SV*)SvRV($arg));
$var = INT2PTR($type, tmp);
}
else
croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")
OUTPUT #
T_PTROBJ_SPECIAL #
sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\",
(void*)$var);
The INPUT and OUTPUT sections substitute underscores for double-colons on
the fly, giving the desired effect. This example demonstrates some of
the power and versatility of the typemap facility.
The "INT2PTR" macro (defined in perl.h) casts an integer to a pointer of
a given type, taking care of the possible different size of integers and
pointers. There are also "PTR2IV", "PTR2UV", "PTR2NV" macros, to map the
other way, which may be useful in OUTPUT sections.
TThhee RRoollee ooff tthhee ttyyppeemmaapp FFiillee iinn YYoouurr DDiissttrriibbuuttiioonn The default typemap in the _l_i_b_/_E_x_t_U_t_i_l_s directory of the Perl source contains many useful types which can be used by Perl extensions. Some extensions define additional typemaps which they keep in their own directory. These additional typemaps may reference INPUT and OUTPUT maps in the main typemap. The xxssuubbpppp compiler will allow the extension’s own typemap to override any mappings which are in the default typemap. Instead of using an additional _t_y_p_e_m_a_p file, typemaps may be embedded verbatim in XS with a heredoc-like syntax. See the documentation on the “TYPEMAP:” XS keyword.
For CPAN distributions, you can assume that the XS types defined by the
perl core are already available. Additionally, the core typemap has
default XS types for a large number of C types. For example, if you
simply return a "char *" from your XSUB, the core typemap will have this
C type associated with the T_PV XS type. That means your C string will
be copied into the PV (pointer value) slot of a new scalar that will be
returned from your XSUB to Perl.
If you're developing a CPAN distribution using XS, you may add your own
file called _t_y_p_e_m_a_p to the distribution. That file may contain typemaps
that either map types that are specific to your code or that override the
core typemap file's mappings for common C types.
SShhaarriinngg ttyyppeemmaappss BBeettwweeeenn CCPPAANN DDiissttrriibbuuttiioonnss Starting with ExtUtils::ParseXS version 3.13_01 (comes with perl 5.16 and better), it is rather easy to share typemap code between multiple CPAN distributions. The general idea is to share it as a module that offers a certain API and have the dependent modules declare that as a built-time requirement and import the typemap into the XS. An example of such a typemap-sharing module on CPAN is “ExtUtils::Typemaps::Basic”. Two steps to getting that module’s typemaps available in your code:
• Declare "ExtUtils::Typemaps::Basic" as a build-time dependency in
"Makefile.PL" (use "BUILD_REQUIRES"), or in your "Build.PL" (use
"build_requires").
• Include the following line in the XS section of your XS file: (don't
break the line)
INCLUDE_COMMAND: $^X -MExtUtils::Typemaps::Cmd
-e "print embeddable_typemap(q{Basic})"
WWrriittiinngg ttyyppeemmaapp EEnnttrriieess Each INPUT or OUTPUT typemap entry is a double-quoted Perl string that will be evaluated in the presence of certain variables to get the final C code for mapping a certain C type.
This means that you can embed Perl code in your typemap (C) code using
constructs such as "${ perl code that evaluates to scalar reference here
}". A common use case is to generate error messages that refer to the
true function name even when using the ALIAS XS feature:
${ $ALIAS ? \q[GvNAME(CvGV(cv))] : \qq[\"$pname\"] }
For many typemap examples, refer to the core typemap file that can be
found in the perl source tree at _l_i_b_/_E_x_t_U_t_i_l_s_/_t_y_p_e_m_a_p.
The Perl variables that are available for interpolation into typemaps are
the following:
• _$_v_a_r - the name of the input or output variable, eg. RETVAL for
return values.
• _$_t_y_p_e - the raw C type of the parameter, any ":" replaced with "_".
e.g. for a type of "Foo::Bar", _$_t_y_p_e is "Foo__Bar"
• _$_n_t_y_p_e - the supplied type with "*" replaced with "Ptr". e.g. for a
type of "Foo*", _$_n_t_y_p_e is "FooPtr"
• _$_a_r_g - the stack entry, that the parameter is input from or output
to, e.g. ST(0)
• _$_a_r_g_o_f_f - the argument stack offset of the argument. ie. 0 for the
first argument, etc.
• _$_p_n_a_m_e - the full name of the XSUB, with including the "PACKAGE"
name, with any "PREFIX" stripped. This is the non-ALIAS name.
• _$_P_a_c_k_a_g_e - the package specified by the most recent "PACKAGE"
keyword.
• _$_A_L_I_A_S - non-zero if the current XSUB has any aliases declared with
“ALIAS”. #
FFuullll LLiissttiinngg ooff CCoorree TTyyppeemmaappss Each C type is represented by an entry in the typemap file that is responsible for converting perl variables (SV, AV, HV, CV, etc.) to and from that type. The following sections list all XS types that come with perl by default.
T_SV #
This simply passes the C representation of the Perl variable (an SV*)
in and out of the XS layer. This can be used if the C code wants to
deal directly with the Perl variable.
T_SVREF #
Used to pass in and return a reference to an SV.
Note that this typemap does not decrement the reference count when
returning the reference to an SV*. See also: T_SVREF_REFCOUNT_FIXED
T_SVREF_FIXED #
Used to pass in and return a reference to an SV. This is a fixed
variant of T_SVREF that decrements the refcount appropriately when
returning a reference to an SV*. Introduced in perl 5.15.4.
T_AVREF #
From the perl level this is a reference to a perl array. From the C
level this is a pointer to an AV.
Note that this typemap does not decrement the reference count when
returning an AV*. See also: T_AVREF_REFCOUNT_FIXED
T_AVREF_REFCOUNT_FIXED #
From the perl level this is a reference to a perl array. From the C
level this is a pointer to an AV. This is a fixed variant of T_AVREF
that decrements the refcount appropriately when returning an AV*.
Introduced in perl 5.15.4.
T_HVREF #
From the perl level this is a reference to a perl hash. From the C
level this is a pointer to an HV.
Note that this typemap does not decrement the reference count when
returning an HV*. See also: T_HVREF_REFCOUNT_FIXED
T_HVREF_REFCOUNT_FIXED #
From the perl level this is a reference to a perl hash. From the C
level this is a pointer to an HV. This is a fixed variant of T_HVREF
that decrements the refcount appropriately when returning an HV*.
Introduced in perl 5.15.4.
T_CVREF #
From the perl level this is a reference to a perl subroutine (e.g.
$sub = sub { 1 };). From the C level this is a pointer to a CV.
Note that this typemap does not decrement the reference count when
returning an HV*. See also: T_HVREF_REFCOUNT_FIXED
T_CVREF_REFCOUNT_FIXED #
From the perl level this is a reference to a perl subroutine (e.g.
$sub = sub { 1 };). From the C level this is a pointer to a CV.
This is a fixed variant of T_HVREF that decrements the refcount
appropriately when returning an HV*. Introduced in perl 5.15.4.
T_SYSRET #
The T_SYSRET typemap is used to process return values from system
calls. It is only meaningful when passing values from C to perl
(there is no concept of passing a system return value from Perl to
C). #
System calls return -1 on error (setting ERRNO with the reason) and
(usually) 0 on success. If the return value is -1 this typemap
returns "undef". If the return value is not -1, this typemap
translates a 0 (perl false) to "0 but true" (which is perl true) or
returns the value itself, to indicate that the command succeeded.
The POSIX module makes extensive use of this type.
T_UV #
An unsigned integer.
T_IV #
A signed integer. This is cast to the required integer type when
passed to C and converted to an IV when passed back to Perl.
T_INT #
A signed integer. This typemap converts the Perl value to a native
integer type (the "int" type on the current platform). When returning
the value to perl it is processed in the same way as for T_IV.
Its behaviour is identical to using an "int" type in XS with T_IV.
T_ENUM #
An enum value. Used to transfer an enum component from C. There is no
reason to pass an enum value to C since it is stored as an IV inside
perl.
T_BOOL #
A boolean type. This can be used to pass true and false values to and
from C.
T_U_INT #
This is for unsigned integers. It is equivalent to using T_UV but
explicitly casts the variable to type "unsigned int". The default
type for "unsigned int" is T_UV.
T_SHORT #
Short integers. This is equivalent to T_IV but explicitly casts the
return to type "short". The default typemap for "short" is T_IV.
T_U_SHORT #
Unsigned short integers. This is equivalent to T_UV but explicitly
casts the return to type "unsigned short". The default typemap for
"unsigned short" is T_UV.
T_U_SHORT is used for type "U16" in the standard typemap.
T_LONG #
Long integers. This is equivalent to T_IV but explicitly casts the
return to type "long". The default typemap for "long" is T_IV.
T_U_LONG #
Unsigned long integers. This is equivalent to T_UV but explicitly
casts the return to type "unsigned long". The default typemap for
"unsigned long" is T_UV.
T_U_LONG is used for type "U32" in the standard typemap.
T_CHAR #
Single 8-bit characters.
T_U_CHAR #
An unsigned byte.
T_FLOAT #
A floating point number. This typemap guarantees to return a variable
cast to a "float".
T_NV #
A Perl floating point number. Similar to T_IV and T_UV in that the
return type is cast to the requested numeric type rather than to a
specific type.
T_DOUBLE #
A double precision floating point number. This typemap guarantees to
return a variable cast to a "double".
T_PV #
A string (char *).
T_PTR #
A memory address (pointer). Typically associated with a "void *"
type.
T_PTRREF #
Similar to T_PTR except that the pointer is stored in a scalar and
the reference to that scalar is returned to the caller. This can be
used to hide the actual pointer value from the programmer since it is
usually not required directly from within perl.
The typemap checks that a scalar reference is passed from perl to XS.
T_PTROBJ #
Similar to T_PTRREF except that the reference is blessed into a
class. This allows the pointer to be used as an object. Most
commonly used to deal with C structs. The typemap checks that the
perl object passed into the XS routine is of the correct class (or
part of a subclass).
The pointer is blessed into a class that is derived from the name of
type of the pointer but with all '*' in the name replaced with 'Ptr'.
For "DESTROY" XSUBs only, a T_PTROBJ is optimized to a T_PTRREF. This
means the class check is skipped.
T_REF_IV_REF #
NOT YET #
T_REF_IV_PTR #
Similar to T_PTROBJ in that the pointer is blessed into a scalar
object. The difference is that when the object is passed back into
XS it must be of the correct type (inheritance is not supported)
while T_PTROBJ supports inheritance.
The pointer is blessed into a class that is derived from the name of
type of the pointer but with all '*' in the name replaced with 'Ptr'.
For "DESTROY" XSUBs only, a T_REF_IV_PTR is optimized to a T_PTRREF.
This means the class check is skipped.
T_PTRDESC #
NOT YET #
T_REFREF #
Similar to T_PTRREF, except the pointer stored in the referenced
scalar is dereferenced and copied to the output variable. This means
that T_REFREF is to T_PTRREF as T_OPAQUE is to T_OPAQUEPTR. All
clear?
Only the INPUT part of this is implemented (Perl to XSUB) and there
are no known users in core or on CPAN.
T_REFOBJ #
Like T_REFREF, except it does strict type checking (inheritance is
not supported).
For "DESTROY" XSUBs only, a T_REFOBJ is optimized to a T_REFREF. This
means the class check is skipped.
T_OPAQUEPTR #
This can be used to store bytes in the string component of the SV.
Here the representation of the data is irrelevant to perl and the
bytes themselves are just stored in the SV. It is assumed that the C
variable is a pointer (the bytes are copied from that memory
location). If the pointer is pointing to something that is
represented by 8 bytes then those 8 bytes are stored in the SV (and
lleennggtthh(()) will report a value of 8). This entry is similar to
T_OPAQUE. #
In principle the uunnppaacckk(()) command can be used to convert the bytes
back to a number (if the underlying type is known to be a number).
This entry can be used to store a C structure (the number of bytes to
be copied is calculated using the C "sizeof" function) and can be
used as an alternative to T_PTRREF without having to worry about a
memory leak (since Perl will clean up the SV).
T_OPAQUE #
This can be used to store data from non-pointer types in the string
part of an SV. It is similar to T_OPAQUEPTR except that the typemap
retrieves the pointer directly rather than assuming it is being
supplied. For example, if an integer is imported into Perl using
T_OPAQUE rather than T_IV the underlying bytes representing the
integer will be stored in the SV but the actual integer value will
not be available. i.e. The data is opaque to perl.
The data may be retrieved using the "unpack" function if the
underlying type of the byte stream is known.
T_OPAQUE supports input and output of simple types. T_OPAQUEPTR can
be used to pass these bytes back into C if a pointer is acceptable.
Implicit array
xsubpp supports a special syntax for returning packed C arrays to
perl. If the XS return type is given as
array(type, nelem)
xsubpp will copy the contents of "nelem * sizeof(type)" bytes from
RETVAL to an SV and push it onto the stack. This is only really
useful if the number of items to be returned is known at compile time
and you don't mind having a string of bytes in your SV. Use T_ARRAY
to push a variable number of arguments onto the return stack (they
won't be packed as a single string though).
This is similar to using T_OPAQUEPTR but can be used to process more
than one element.
T_PACKED #
Calls user-supplied functions for conversion. For "OUTPUT" (XSUB to
Perl), a function named "XS_pack_$ntype" is called with the output
Perl scalar and the C variable to convert from. $ntype is the
normalized C type that is to be mapped to Perl. Normalized means that
all "*" are replaced by the string "Ptr". The return value of the
function is ignored.
Conversely for "INPUT" (Perl to XSUB) mapping, the function named
"XS_unpack_$ntype" is called with the input Perl scalar as argument
and the return value is cast to the mapped C type and assigned to the
output C variable.
An example conversion function for a typemapped struct "foo_t *"
might be:
static void
XS_pack_foo_tPtr(SV *out, foo_t *in)
{
dTHX; /* alas, signature does not include pTHX_ */
HV* hash = newHV();
hv_stores(hash, "int_member", newSViv(in->int_member));
hv_stores(hash, "float_member", newSVnv(in->float_member));
/* ... */
/* mortalize as thy stack is not refcounted */
sv_setsv(out, sv_2mortal(newRV_noinc((SV*)hash)));
}
The conversion from Perl to C is left as an exercise to the reader,
but the prototype would be:
static foo_t *
XS_unpack_foo_tPtr(SV *in);
Instead of an actual C function that has to fetch the thread context
using "dTHX", you can define macros of the same name and avoid the
overhead. Also, keep in mind to possibly free the memory allocated by
"XS_unpack_foo_tPtr".
T_PACKEDARRAY #
T_PACKEDARRAY is similar to T_PACKED. In fact, the "INPUT" (Perl to
XSUB) typemap is identical, but the "OUTPUT" typemap passes an
additional argument to the "XS_pack_$ntype" function. This third
parameter indicates the number of elements in the output so that the
function can handle C arrays sanely. The variable needs to be
declared by the user and must have the name "count_$ntype" where
$ntype is the normalized C type name as explained above. The
signature of the function would be for the example above and "foo_t
**":
static void
XS_pack_foo_tPtrPtr(SV *out, foo_t *in, UV count_foo_tPtrPtr);
The type of the third parameter is arbitrary as far as the typemap is
concerned. It just has to be in line with the declared variable.
Of course, unless you know the number of elements in the "sometype
**" C array, within your XSUB, the return value from "foo_t **
XS_unpack_foo_tPtrPtr(...)" will be hard to decipher. Since the
details are all up to the XS author (the typemap user), there are
several solutions, none of which particularly elegant. The most
commonly seen solution has been to allocate memory for N+1 pointers
and assign "NULL" to the (N+1)th to facilitate iteration.
Alternatively, using a customized typemap for your purposes in the
first place is probably preferable.
T_DATAUNIT #
NOT YET #
T_CALLBACK #
NOT YET #
T_ARRAY #
This is used to convert the perl argument list to a C array and for
pushing the contents of a C array onto the perl argument stack.
The usual calling signature is
@out = array_func( @in );
Any number of arguments can occur in the list before the array but
the input and output arrays must be the last elements in the list.
When used to pass a perl list to C the XS writer must provide a
function (named after the array type but with 'Ptr' substituted for
'*') to allocate the memory required to hold the list. A pointer
should be returned. It is up to the XS writer to free the memory on
exit from the function. The variable "ix_$var" is set to the number
of elements in the new array.
When returning a C array to Perl the XS writer must provide an
integer variable called "size_$var" containing the number of elements
in the array. This is used to determine how many elements should be
pushed onto the return argument stack. This is not required on input
since Perl knows how many arguments are on the stack when the routine
is called. Ordinarily this variable would be called "size_RETVAL".
Additionally, the type of each element is determined from the type of
the array. If the array uses type "intArray *" xsubpp will
automatically work out that it contains variables of type "int" and
use that typemap entry to perform the copy of each element. All
pointer '*' and 'Array' tags are removed from the name to determine
the subtype.
T_STDIO #
This is used for passing perl filehandles to and from C using "FILE
*" structures.
T_INOUT #
This is used for passing perl filehandles to and from C using "PerlIO
*" structures. The file handle can used for reading and writing. This
corresponds to the "+<" mode, see also T_IN and T_OUT.
See perliol for more information on the Perl IO abstraction layer.
Perl must have been built with "-Duseperlio".
There is no check to assert that the filehandle passed from Perl to C
was created with the right "open()" mode.
Hint: The perlxstut tutorial covers the T_INOUT, T_IN, and T_OUT XS
types nicely.
T_IN #
Same as T_INOUT, but the filehandle that is returned from C to Perl
can only be used for reading (mode "<").
T_OUT #
Same as T_INOUT, but the filehandle that is returned from C to Perl
is set to use the open mode "+>".
perl v5.36.3 2017-02-05 PERLXSTYPEMAP(1)