Chapter 8

Creation

The simplest way to create an AV is to use the newAV() function:

AV *av = newAV();

If you have an array of SV*s, then you can create an array from them using 

av_make():

AV *av;

SV *sv_array[3];

sv_array[0] = newSVpv("foo",0);

sv_array[1] = newSVpv("bar",0);

sv_array[2] = newSVpv("baz",0);

av = av_make(3, sv_array);     // create an array from the three SVs

Fetching Values

AVs support access by index as well as the familiar pop and shift operations. You 

can fetch an SV from an array using the av_fetch() function:

SV **svp;

svp = av_fetch(av, 10, 0); // fetch $av[10] (the 0 indicates this isn t an

                           // lvalue)

if (!svp) croak("fetch failed: av doesn t have a tenth element!");

Notice that the return value from av_fetch() is a pointer to a pointer to SV (that is, 

an SV**) not a normal pointer to SV (that is, SV*). If you try to fetch a value that 

doesn't exist, then av_fetch() will return a NULL pointer. Be sure to check the return 

value before dereferencing or you'll end up with a segmentation fault if the ele 

ment doesn't exist. The preceding code checks the return value and calls croak() 

the Perl API version of die if av_fetch() returns NULL.

However, you can skip testing the return value from av_fetch() if you know the 

element exists. You can get this information using av_exists(), which tests whether 

an index exists in an AV:

SV *sv;

if (av_exists(av, 9)) {         // check that the 10th element exists

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

} else {

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

}

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