CHAPTER 8

Programming Perl in C

T

HE NEXT THREE CHAPTERS

 teach a black art programming Perl modules in C. To 

get the most out of these chapters you'll need to have some experience with the C 

programming language. You don't need to be a C guru, but you do need to know 

your pointers and macros. If you're worried that you don't know enough C, I 

suggest you buy a good C reference and give it a try. When you get stuck, hit the 

books I think you'll find it happening less often than you expect.

This chapter presents an introduction to Perl's C API. Next, the XS system is pre 

sented in Chapter 9. XS is the system used by the vast majority of C modules on CPAN 

today. Finally, in Chapter 10, I'll show you a shortcut Inline::C. Inline::C is a brand 

new module that I predict will be used for the majority C modules in the future.

One thing this chapter won't do is explain how Perl works. This is fascinating 

material but largely unrelated to the task of writing Perl modules in C. For pointers 

to documentation on this and other related topics, see the  References  section at 

the end of the chapter.

Why C?

Writing Perl modules in C is a lot more work than writing them in Perl. The end 

result is likely to be buggier and less portable than an equivalent implementation 

in Perl. As such, you should be hesitant to write in C unless you have a good reason.

So, what constitutes a good reason? The best reason is simple: because you 

have to. There are times when Perl simply cannot do what you need done. For 

example, when you need to interface with a library written in C, you have no choice 

but to write some C code. CPAN contains numerous examples of this type of 

module Tk, GD, most of the DBD drivers, and many more. When you come 

across a C library that provides a new service, you should consider it a great oppor 

tunity to create a new CPAN module.

A common, often misguided, reason to create Perl modules in C is to increase 

performance. The reasoning is misguided because the Perl interpreter itself is 

written in C. Thus most of what a Perl program does is already happening in highly 

optimized C code. You have to believe you can do better than the C gurus that 

created Perl to think that your module will be faster simply by being written in C.

1

1. Mark Jason Dominus's article  Why Not Translate Perl to C?  on Perl.com contains an 

extended proof of this assertion. You can find the article at http://www.perl.com/pub/a/2001/

06/27/ctoperl.html.

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