Programming Perl in C

You can get the same effect using av_len() to check the length of the array:

SV *sv;

if (av_len(av) >= 9) {          // check that $#av >= 9

   sv = *(av_fetch(av, 9, 0));  // safely trust av_fetch to return non NULL

} else {

   croak("av doesn t have a tenth element!");

}

The av_len() function works the same way as the $#array magic value it returns 

the last valid index in an array.

Combining the preceding functions, you can now write a function to iterate 

through an array and print out each value:

void print_array (AV *av) {

   SV    *sv;     // SV pointer to hold return from array

   char  *string; // string pointer to hold SV string value

   STRLEN len;    // unused length value for SvPV()

   I32 i = 0;     // loop counter

   // loop over all valid indexes

   for (i = 0; i <= av_len(av); i++) {

      sv = *(av_fetch(av, i, 0));   // get the SV for this index

      string = SvPV(sv, len);       // get a stringified form of the SV

      printf("%s\n", string);       // print it out, one value per line

    }

}

As I mentioned earlier, AVs also support a version of Perl's pop and shift built 

ins. These functions, av_pop() and av_shift(), return regular SV* pointers rather 

than the SV** pointers returned by av_fetch(). Using av_shift(), you could write a 

destructive version of the for loop just shown:

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