# parse_c.rb

Path: | rdoc/parsers/parse_c.rb
Last Update: | Sat Oct 15 23:44:29 AUS Eastern Standard Time 2005

We attempt to parse C extension files. Basically we look for the standard patterns that you find in extensions: `rb_define_class, rb_define_method` and so on. We also try to find the corresponding C source for the methods and extract comments, but if we fail we don’t worry too much.

The comments associated with a Ruby method are extracted from the C comment block associated with the routine that implements that method, that is to say the method whose name is given in the `rb_define_method` call. For example, you might write:

     /*
      * Returns a new array that is a one-dimensional flattening of this
      * array (recursively). That is, for every element that is an array,
      * extract its elements into the new array.
      *
      *    s = [ 1, 2, 3 ]           #=> [1, 2, 3]
      *    t = [ 4, 5, 6, [7, 8] ]   #=> [4, 5, 6, [7, 8]]
      *    a = [ s, t, 9, 10 ]       #=> [[1, 2, 3], [4, 5, 6, [7, 8]], 9, 10]
      *    a.flatten                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
      */
      static VALUE
      rb_ary_flatten(ary)
          VALUE ary;
      {
          ary = rb_obj_dup(ary);
          rb_ary_flatten_bang(ary);
          return ary;
      }

      ...

      void
      Init_Array()
      {
        ...
        rb_define_method(rb_cArray, "flatten", rb_ary_flatten, 0);

Here RDoc will determine from the rb_define_method line that there’s a method called "flatten" in class Array, and will look for the implementation in the method rb_ary_flatten. It will then use the comment from that method in the HTML output. This method must be in the same source file as the rb_define_method.

C classes can be diagramed (see /tc/dl/ruby/ruby/error.c), and RDoc integrates C and Ruby source into one tree

The comment blocks may include special direcives:

Document-class: name
  This comment block is documentation for the given class. Use this when the `Init_xxx` method is not named after the class.
Document-method: name
  This comment documents the named method. Use when RDoc cannot outomatically find the method from it’s declaration
call-seq: text up to an empty line
  Because C source doesn’t give descripive names to Ruby-level parameters, you need to document the calling sequence explicitly

In additon, RDoc assumes by default that the C method implementing a Ruby function is in the same source file as the rb_define_method call. If this isn’t the case, add the comment

       rb_define_method(....);  // in: filename

As an example, we might have an extension that defines multiple classes in its Init_xxx method. We could document them using

     /*
      * Document-class:  MyClass
      *
      * Encapsulate the writing and reading of the configuration
      * file. ...
      */

     /*
      * Document-method: read_value
      *
      * call-seq:
      *   cfg.read_value(key)            -> value
      *   cfg.read_value(key} { |key| }  -> value
      *
      * Return the value corresponding to +key+ from the configuration.
      * In the second form, if the key isn't found, invoke the
      * block and return its value.
      */

### Required files

rdoc/code_objects rdoc/parsers/parserfactory

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