As the tree of opcodes constituting a compiled Perl program is executed, Perl values are created, manipulated, and destroyed. The data types you're familiar with in Perl all have corresponding data types in the C under Perl's hood, and you'll need to know about those types when you pass data between the two languages.
Three C typedefs correspond to Perl's three basic data
types: the SV
(scalar value), AV
(array value), and HV
(hash value). In addition, an
IV
is a simple signed integer type guaranteed to be
large enough to hold either a pointer or an integer; and
I32
and I16
are types guaranteed
to be large enough to hold 32 bits and 16 bits, respectively. For
storing unsigned versions of these last three typedefs, there exist
UV
, U32
, and
U16
typedefs as well. All of these typedefs can be
manipulated with the C functions described in the
perlguts documentation. We sketch the behaviors
of some of those functions below:
There are four types of values that can be copied into an
SV
: an integer value (IV
), a
double (NV
), a string (PV
),
and another scalar (SV
). There are dozens of
functions for SV
s to let you create, modify,
grow, and check for the truth or definedness of the Perl scalars
they represent. Perl references are implemented as an
RV
, a special type of
SV
.
When an AV
is created, it can be created
empty or populated with SV
s, which makes sense
since an array is a collection of scalars.
The HV
has associated C functions for
storing, fetching, deleting, and checking for the existence of
key/value pairs in the hash the HV
represents.
There is also a GV
(glob value), which
can hold references to any of the values associated with a
variable identifier: a scalar value, an array value, a hash value,
a subroutine, an I/O handle, or a format.
When you extend Perl, you will sometimes need to know about these values when you create bindings to C functions. When you embed Perl, you'll need to know about these values when you exchange data with the Perl interpreter included in your C program.