# SWIG:Examples:perl5:simple

`SWIG/Examples/perl5/simple/`

## Simple Perl5 Example

`$Header$`

This example illustrates how you can hook Perl to a very simple C program containing a function and a global variable.

## The C Code

Suppose you have the following C code:

>     /* File : example.c */

>     /* A global variable */
>     double Foo = 3.0;

>     /* Compute the greatest common divisor of positive integers */
>     int gcd(int x, int y) {
>       int g;
>       g = y;
>       while (x > 0) {
>         g = x;
>         x = y % x;
>         y = g;
>       }
>       return g;
>     }

## The SWIG interface

Here is a simple SWIG interface file:

>     /* File: example.i */
>     %module example

>     extern int gcd(int x, int y);
>     extern double Foo;

## Compilation

1. `swig -perl5 example.i`

2. This produces two files: `example_wrap.c` and `example.pm`.

3. Compile `example_wrap.c` and `example.c` to create the extension `example.so`.

## Using the extension

Click here to see a script that calls our C functions from Perl.

## Key points

- Use the `use` statement to load your extension module from Perl. For example:

  >     use example;

- C functions work just like Perl functions. For example:

  >     $g = example::gcd(42,105);

- C global variables are accessed like ordinary Perl variables. For example:

  >     $a = $example::Foo;