Chapter 8

That said, sometimes you can write faster code in C than in Perl. After careful 

profiling and tuning, sometimes it turns out that 90 percent of your module's 

runtime is taking place inside a small section of code. If you can replace this piece 

with a call to a function written in carefully crafted C, you might realize significant 

gains. The watchword here is profiling: You need to find the bottleneck and be sure 

you can't optimize it using more conventional techniques.

One place where C does have a notable advantage over Perl in performance is 

in memory usage. C requires you to be entirely responsible for every memory allo 

cation; as a result, you gain a much higher degree of control over how your data is 

stored. Sometimes this can be used to allow your programs to run in a much 

smaller amount of memory than a Perl implementation would.

2

The Perl C API

To write Perl modules in C, you need to have a working knowledge of the Perl C API 

(Perl API for short). This section will give you the basics, but you should know 

where to go for the details: perlapi. The perlapi documentation that comes with 

Perl is the Perl API bible. Nearly every C function and macro that Perl supports is 

listed there along with descriptions generated from comments in the Perl source.

Data Types

For every data type available to Perl programmers, there is a corresponding C type 

(see Table 8 1). Perl's data types are a lot like objects in that they each have a set of 

functions that operate on them. Note that these data types are always manipu 

lated through pointers.

Table 8 1. Perl Data Types

Type 

Full Name

Perl Example

SV*

Scalar value

$scalar

AV*

Array value

@array

HV*

Hash value

%hash

CV*

Code value

&sub

GV*

Glob value

*glob

2. But before you decide this describes your problem, make sure you check out Bit::Vector by 

Steffen Beyer and the many modules that use it to efficiently store data.

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