Programming Perl in C

// print out the returned counts, in reverse order

for(i = num; i > 0; i++) {

  printf("count %d: %d\n", i, SvIV(POPs));

}

FREETMPS; LEAVE;                        // end the scope   freeing mortal

                                        // variables

There are two new pieces in this example. First, the call is made using the G_ARRAY

option indicating that I expect to get a list of return values back. Also, the return 

value from call_pv(), the number of values returned on the stack, is saved. Then a 

loop is run that prints out the values in reverse order. A more elaborate loop could 

be written to process the return values in the  correct  order, but since POPs works 

in reverse, it's easiest to follow suit.

Signaling Errors

There are two ways to return from a Perl subroutine by using return() or by gen 

erating an exception with die(). The interface to die() from the C API is croak(),

which supports a printf() style interface for generating exception strings:

croak("Big trouble, Indy, the %s has got the %s!", villain, bauble);

A warning, provided by the warn() function in Perl, can be produced using the 

warn() API function:

warn("Ouch, don t touch that, %s!", SvPVX(name_sv));

This is an unconditional warning it will always generate output no matter what 

the state of the warnings pragma. If you want to check whether warnings are on or 

not, you can use the isLEXWARN_on macro:

7

if (isLEXWARN_on) warn("You use warnings; good for you!");

You can also test if a particular category of warnings is on using the ckWARN macro:

8

if (ckWARN(WARN_DEPRECATED)) warn("Use of this function is deprecated.");

The constants used by this macro are lists in the warnings.h file in the Perl source.

7. Which isn't listed in perlapi and as such may change without notice

8. Also not listed in perlapi beware!

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