Chapter 8

Dereferencing

Once you know what kind of object an RV points to, you can safely cast the return 

value to the correct type:

AV *av;

if (SvTYPE(SvRV(sv_rv)) == SVt_PVAV) {

   av = (AV *) SvRV(sv_rv); // safely cast dereferenced value to an AV

} else {

   croak("sv_rv isn t a reference to an array!");

}

CAUTION Always check your RVs with SvROK and SvTYPE before casting 

them. It's all too common for C modules to crash when passed a normal 

scalar where they were expecting a reference. It's much nicer to print an 

error message!

Memory Management

So far I've ignored memory management. As a result, most of the preceding 

examples will leak memory.

6

 This is because, unlike Perl, C expects you to manage 

both allocation and deallocation. The Perl API offers some help in this area, and 

learning to use it correctly is the key to creating C modules that don't leak memory.

Reference Counts

Perl uses an explicit reference counting garbage collector to manage memory. 

This means that every object (SV, AV, HV, and so on) created by Perl has a number 

associated with it called a reference count, or refcount for short. A reference count 

is simply a count of the number of objects that refer to the object. When the ref 

erence count of an object reaches 0, the memory used by the object is freed by the 

garbage collector.

6. A piece of code is said to leak memory when it fails to deallocate memory that is no longer 

being used. The classic test for memory leaks is to run a piece of code inside a loop and watch 

to see if the memory used by the program grows over time.

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