mirror of
https://github.com/cookiengineer/audacity
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89 lines
3.1 KiB
XML
89 lines
3.1 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
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"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">
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<chapter id="objects">
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<title>Objects in C</title>
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<para>
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Redland uses objects and is written in C, which has no built in support for
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object construction, destruction, copying etc. This library thus uses
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conventions for the names of the routines providing the
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constructor, destructor and copy constructor functionality for a class as
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well as conventions for the general methods.
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</para>
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<para>
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A class FOO is defined as a C typedef <literal>librdf_foo</literal>,
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and its a public interface defined in <filename>rdf_foo.h</filename>
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along with any public or private types, enumerations or constants.
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The private definitions are not exposed to library users, only
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internally when the library is built. The implementation of the
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class is defined in file <filename>rdf_foo.c</filename> and may
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include private (static) functions either for internal
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implementations or to satisfy part of a factory API.
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</para>
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<para>Each class may have a class initialiser / termination pair
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of functions which must be called before any object in the class is created,
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and after the last object has been freed. These are defined with signatures
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like:
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<programlisting>
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void init_librdf_foo (...)
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void terminate_librdf_foo (void)
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</programlisting>
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The arguments to the initialisation vary since there are sometimes
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some class wide options that can be set at initialisation time.
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</para>
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<para>
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The object constructor(s) are defined with signatures like:
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<programlisting>
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librdf_foo* librdf_new_foo(void)
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</programlisting>
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which takes no parameters. Additional constructors can be defined
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with parameters, and are named in a similar way with an extra part
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appropriate for the name for example:
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<programlisting>
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librdf_foo* librdf_new_foo_with_options(char *options)
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</programlisting>
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</para>
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<para>A copy constructor may be defined which will have the signature:
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<programlisting>
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librdf_foo* librdf_new_foo_from_foo(librdf_foo* old_foo)
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</programlisting>
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</para>
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<para>A destructor must be defined and has the signature:
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<programlisting>
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void librdf_free_foo(librdf_foo* foo)
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</programlisting>
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</para>
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<para>Methods of the class have names starting with <literal>librdf_foo_</literal> and
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examples could be:
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<programlisting>
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/* accessor functions to object part 'thing' */
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int librdf_foo_set_thing(librdf_foo* foo, char *thing)
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char *librdf_foo_get_thing(librdf_foo* foo)
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</programlisting>
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</para>
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<para>It is often convienent to get a string representation of an
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object for further processing, debugging or serialisation. There are
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two conventions for methods that provide this functionality - the
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first is when a pointer is returned to a <emphasis>shared</emphasis>
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copy of the string and in that case the method ends
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<literal>_as_string</literal>. The second is when a pointer is
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returned to a <emphasis>newly allocated</emphasis> string in which
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case the method ends <literal>_to_string</literal>.</para>
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</chapter>
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<!--
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Local variables:
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mode: sgml
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sgml-parent-document: ("redland-docs.xml" "book" "part" "chapter")
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End:
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-->
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