Writing C Modules with XS

Supporting Named Parameters

In Perl, a better interface to the preceding MIME type functions might be this one:

$type = Gnome::MIME::file_type(filename     => $filename,

                               default_type => "text/html",

                               read_file    => 1);

This follows the named parameter function style introduced in Chapter 2.

Using XS

Unfortunately XS doesn't have native support for this highly Perl ish function style, 

but it's not hard to support it with a little code (see Listing 9 6 for the full XSUB).

Listing 9 6. Named Parameter XSUB

const char *

file_type(...)

PREINIT:

  char *filename = NULL;     // variables for named params

  char *default_type = NULL;

  IV read_file = 0;

  IV x;                      // loop counter

CODE:

  // check that there are an even number of args

  if (items % 2) croak("Usage: Gnome::MIME::file_type(k => v, ...)");

  // loop over args by pairs and fill in parameters

  for(x = 0; x < items; x+=2) {

    char *key = SvPV(ST(x), PL_na);

    if (strEQ(key, "filename")) {

      filename = SvPV(ST(x+1), PL_na);

    } else if (strEQ(key, "default_type")) {

      default_type = SvPV(ST(x+1), PL_na);

    } else if (strEQ(key, "read_file")) {

      read_file = SvIV(ST(x+1));

    } else {

      croak("Unknown key found in Gnome::MIME::file_type parameter list: %s",

                  SvPV(ST(x), PL_na));

    }

  }

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