XS help

Thelonius has asked for the wisdom of the Perl Monks concerning the following question:

I'm fairly new to writing XS routines. I'm wrapping a routine
HPERRMSG(displaycode,depth,errorproc,errornum, buffer,buflength,status);
Where all parameters except the first are optional. Among other things, the routine can format an error message (passed in as errornum) into a text message in buffer.

So, what I coded after several tries is:

void
hperrmsg(displaycode,...)
    int displaycode
   PROTOTYPE: $;@
   PREINIT:
        int depth=0;
        int errornum=0;
        SV *buffer=NULL;
        char *pbuf;
        short buflength=0;
        int status=0;
        int parm_ct;
   CODE:

     /* ... other items omitted for clarity */

     if (items > 4) {
      buffer = ST(4);
     }

     if (buffer == NULL || SvREADONLY(buffer)) {
       pbuf = NULL;
     } else {
       int tmplen=buflength+1;
       if (!SvPOK(buffer)) {
         SvPV_force(buffer, tmplen);
       } else {
         SvGROW(buffer+1, tmplen);
       }
       pbuf = SvPVX(buffer);
     }



      HPERRMSG(parm_ct, displaycode, depth, 0, errornum,
                        pbuf, &buflength, &status);

      if (buflength) {
          pbuf[buflength] = '\0';  
          SvPOK_on(buffer);
          SvCUR_set(buffer, buflength);
      }
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This works, but is it the right thing to do? I put in the check for SvREADONLY thinking the user might put in "undef" as a placeholder.

Any feedback?

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Re: XS help by MZSanford (Curate) on Oct 17, 2001 at 12:40 UTC
I have written very few (2) XS modules for wrapping other code, and a few XS modules for companies from scratch ... making me less than an authority on XS, but from what i see here, this code should work very well. I would assume that <code lang="C">HPERRMSG()</code> allows for a `NULL` `pbuf`, but not knowing the function, depending on what this is, you may want to return if it is `NULL` ... but since i don't know <code lang="C">HPERRMSG()</code>, i am possibly very wrong. Last thing, and this is just me, i would suggest returning a status of some sort. Something as simple as `1` on success and <code lang="C">PL_undef</code> for failure. That way, even if <code lang="C">HPERRMSG()</code> returns `void`, you can return in the event of bad arguments (non-numeric, etc) my $cents = 2;	[reply] [d/l] [select]

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Re: XS help
by MZSanford (Curate) on Oct 17, 2001 at 12:40 UTC

NULL

pbuf

NULL

1

void

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