SWIG and Pike

# 30 SWIG and Pike

- Preliminaries
  - Running SWIG
  - Getting the right header files
  - Using your module
- Basic C/C++ Mapping
  - Modules
  - Functions
  - Global variables
  - Constants and enumerated types
  - Constructors and Destructors
  - Static Members

This chapter describes SWIG support for Pike. As of this writing, the SWIG Pike module is still under development and is not considered ready for prime time. The Pike module is being developed against the Pike 7.4.10 release and may not be compatible with previous versions of Pike.

This chapter covers most SWIG features, but certain low-level details are covered in less depth than in earlier chapters. At the very least, make sure you read the "SWIG Basics" chapter.

## 30.1 Preliminaries

### 30.1.1 Running SWIG

Suppose that you defined a SWIG module such as the following:

    %module example

    %{
    #include "example.h"
    %}

    int fact(int n);

To build a C extension module for Pike, run SWIG using the `-pike` option :

    $ swig -pike example.i

If you're building a C++ extension, be sure to add the `-c++` option:

    $ swig -c++ -pike example.i

This creates a single source file named `example_wrap.c` (or `example_wrap.cxx`, if you ran SWIG with the `-c++` option). The SWIG-generated source file contains the low-level wrappers that need to be compiled and linked with the rest of your C/C++ application to create an extension module.

The name of the wrapper file is derived from the name of the input file. For example, if the input file is `example.i`, the name of the wrapper file is `example_wrap.c`. To change this, you can use the `-o` option:

    $ swig -pike -o pseudonym.c example.i

### 30.1.2 Getting the right header files

In order to compile the C/C++ wrappers, the compiler needs to know the path to the Pike header files. These files are usually contained in a directory such as

    /usr/local/pike/7.4.10/include/pike

There doesn't seem to be any way to get Pike itself to reveal the location of these files, so you may need to hunt around for them. You're looking for files with the names `global.h`, `program.h` and so on.

### 30.1.3 Using your module

To use your module, simply use Pike's `import` statement:

    $ pike
    Pike v7.4 release 10 running Hilfe v3.5 (Incremental Pike Frontend)
    > import example;
    > fact(4);
    (1) Result: 24

## 30.2 Basic C/C++ Mapping

### 30.2.1 Modules

All of the code for a given SWIG module is wrapped into a single Pike module. Since the name of the shared library that implements your module ultimately determines the module's name (as far as Pike is concerned), SWIG's `%module` directive doesn't really have any significance.

### 30.2.2 Functions

Global functions are wrapped as new Pike built-in functions. For example,

    %module example

    int fact(int n);

creates a new built-in function `example.fact(n)` that works exactly as you'd expect it to:

    > import example;
    > fact(4);
    (1) Result: 24

### 30.2.3 Global variables

Global variables are currently wrapped as a pair of of functions, one to get the current value of the variable and another to set it. For example, the declaration

    %module example

    double Foo;

will result in two functions, `Foo_get()` and `Foo_set()`:

    > import example;
    > Foo_get();
    (1) Result: 3.000000
    > Foo_set(3.14159);
    (2) Result: 0
    > Foo_get();
    (3) Result: 3.141590

### 30.2.4 Constants and enumerated types

Enumerated types in C/C++ declarations are wrapped as Pike constants, not as Pike enums.

### 30.2.5 Constructors and Destructors

Constructors are wrapped as `create()` methods, and destructors are wrapped as `destroy()` methods, for Pike classes.

### 30.2.6 Static Members

Since Pike doesn't support static methods or data for Pike classes, static member functions in your C++ classes are wrapped as regular functions and static member variables are wrapped as pairs of functions (one to get the value of the static member variable, and another to set it). The names of these functions are prepended with the name of the class. For example, given this C++ class declaration:

    class Shape
    {
    public:
        static void print();
        static int nshapes;
    };

SWIG will generate a `Shape_print()` method that invokes the static `Shape::print()` member function, as well as a pair of methods, `Shape_nshapes_get()` and `Shape_nshapes_set()`, to get and set the value of `Shape::nshapes`.