Re: Call variable length argument function from perl -> C using autogenerated code from xsubpp

The mm_array_push routine I sent is by definition a variable-length
parameter list XS routine because it uses the '...' notation.  This
is a feature of XS that allows perl callers to include as many
parameters at the end of a call as they like.  I'm sure that you have
read the documentation of the XS feature at
http://perldoc.perl.org/perlxs.html#Variable-length-Parameter-Lists

This feature has the same objective as the same notation '...' in C,
but I'm pretyy sure the XS feature was never intended to provide an
automatic interface to C functions that use this notation.  The
latter feature is documented nicely at
http://en.wikipedia.org/wiki/ 
Variadic_function#Variadic_functions_in_C.2C_Objective-C.2C_C.2B.2B. 
2C_and_D

The problem of using the former to interface the latter is discussed at
http://www.perlmonks.org/?node_id=684623
You might find it useful to email the perlmonks correspondent who
started the thread above, to ask if he found a solution he liked.

For any given routine, it would be pretty simple to write an interface
routine that accumulates the variable operands in an array (like my
mm_array_push does).  The other half of the solution would be to
modify the C target routine to receive a pointer to the array as an
operand, and use it rather than an internal 'va_list' as described
in the second link above.  But this is not automatic in the sense
you want.

Best Regards,
cmac


On Mar 2, 2011, at 10:22 AM, Harakiri wrote:

> Thank you, but it seems you manually created the XS mm_array_push  
> (array, ...) stub logic and then used to translate it with xsubpp,  
> besides this looks like an array not an var argument list
>
> i only have a simple header file with my function signatures and  
> generic xs where this header is included
>
>
> --- On Wed, 3/2/11, [email protected]  
> <[email protected]> wrote:
>
>> From: [email protected] <[email protected]>
>> Subject: Re: Call variable length argument function from perl -> C  
>> using autogenerated code from xsubpp
>> To: "Harakiri" <[email protected]>
>> Cc: [email protected]
>> Date: Wednesday, March 2, 2011, 12:41 PM
>> var arg lists are supported in perl
>> -> c.
>> Here is an interface routine (from a .xs file) that
>> implements
>> pushing into an array:
>>
>> UV
>> mm_array_push (array, ...)
>>     mm_array *array
>>     ALIAS:
>>         mma_array_push=1
>>     PREINIT:
>>         int add_count = items - 1;
>>         SV *addSVs[add_count];
>>         int i;
>>     CODE:
>>         for (i=0; i < add_count; i++) addSVs[i] = ST(i+1);
>>         if (!mm_array_splice (array, array->entries, 0, NULL,
>>             add_count, addSVs, ix) && PL_dowarn && mm_error())
>>             warn ("IPC::MMA: %s", mm_error());
>>         RETVAL = array->entries;
>>     OUTPUT:
>>         RETVAL
>>
>> This routine is converted by xsubpp into the one below by
>> the
>> following automatic step in the module's 'make' stage:
>> /usr/bin/perl /usr/local/lib/perl5/5.10.1/ExtUtils/xsubpp
>> -typemap /usr/local/lib/perl5/5.10.1/ExtUtils/typemap
>> -typemap typemap  MMA.xs > MMA.xsc && mv
>> MMA.xsc MMA.c
>>
>>
>> XS(XS_IPC__MMA_mm_array_push)
>> {
>> #ifdef dVAR
>>     dVAR; dXSARGS;
>> #else
>>     dXSARGS;
>> #endif
>>     dXSI32;
>>     if (items < 1)
>>        croak_xs_usage(cv,
>> "array, ...");
>>     {
>>     mm_array *    array;
>> #line 1771 "MMA.xs"
>>         int add_count = items - 1;
>>         SV *addSVs[add_count];
>>         int i;
>> #line 2427 "MMA.c"
>>     UV    RETVAL;
>>     dXSTARG;
>>
>>     if (sv_derived_from(ST(0),
>> "mm_arrayPtr")) {
>>         IV tmp =
>> SvIV((SV*)SvRV(ST(0)));
>>         array = INT2PTR(mm_array
>> *,tmp);
>>     }
>>     else
>>         Perl_croak(aTHX_ "%s: %s
>> is not of type %s",
>>
>> GvNAME(CvGV(cv)),
>>
>> "array", "mm_arrayPtr");
>> #line 1775 "MMA.xs"
>>         for (i=0; i < add_count;
>> i++) addSVs[i] = ST(i+1);
>>         if (!mm_array_splice (array,
>> array->entries, 0, NULL, add_count, addSVs, ix)
>>          && PL_dowarn
>> && mm_error()) warn ("IPC::MMA: %s", mm_error());
>>         RETVAL = array->entries;
>> #line 2444 "MMA.c"
>>     XSprePUSH; PUSHu((UV)RETVAL);
>>     }
>>     XSRETURN(1);
>> }
>>
>> On Mar 2, 2011, at 8:19 AM, Harakiri wrote:
>>
>>> Hello,
>>>
>>> i've searched the mailing list and found an entry from
>> 2001 that var arg list were not supported in perl -> c :
>>>
>>> http://www.mail-archive.com/[email protected]/msg00345.html
>>>
>>> Has this changed?
>>>
>>> Im using the xsubpp util to create my glue cpp
>> classes.
>>>
>>> Example:
>>>
>>> static int Random( int Count, ... );
>>>
>>> turns into
>>>
>>> XS(XS_MyClass_Random)
>>> {
>>>          dXSARGS;
>>>          if (items <
>> 2)
>>>
>>    Perl_croak(aTHX_ "Usage:
>> MyClass::Random(CLASS, Count, ...)");
>>>          {
>>>
>>    char *
>> CLASS = (char *)SvPV_nolen(ST(0));
>>>
>>    int
>>    RETVAL;
>>>
>>    dXSTARG;
>>>
>>    int
>>    Count = (int)SvIV(ST(1));
>>>
>>>
>>    RETVAL = MyClass::Random(Count);
>>>
>>    XSprePUSH; PUSHi((IV)RETVAL);
>>>          }
>>>          XSRETURN(1);
>>> }
>>>
>>> as you can see the "..." is not honored, only the
>> first argument is used. I know i could manually glue this
>> somehow but i DONT want that because i have alot of method
>> signatures which always have been converted fine using
>> xsubpp - i dont want to manually alter the generated file
>> just for one method.
>>>
>>> Is there a way?
>>>
>>> Thank you!
>>>
>>>
>>>
>>
>>
>
>
>