glib/tmpl/conversions.sgml

<!-- ##### SECTION Title ##### -->
Character Set Conversion

<!-- ##### SECTION Short_Description ##### -->
convert strings between different character sets using iconv()

<!-- ##### SECTION Long_Description ##### -->
<para>

</para>

    <refsect2 id="file-name-encodings">
      <title>File Name Encodings</title>

      <para>
	Historically, Unix has not had a defined encoding for file
	names:  a file name is valid as long as it does not have path
	separators in it ("/").  However, displaying file names may
	require conversion:  from the character set in which they were
	created, to the character set in which the application
	operates.  Consider the Spanish file name
	"<filename>Presentaci&oacute;n.sxi</filename>".  If the
	application which created it uses ISO-8859-1 for its encoding,
	then the actual file name on disk would look like this:
      </para>

      <programlisting id="filename-iso8859-1">
Character:  P  r  e  s  e  n  t  a  c  i  &oacute;  n  .  s  x  i
Hex code:   50 72 65 73 65 6e 74 61 63 69 f3 6e 2e 73 78 69
      </programlisting>

      <para>
	However, if the application use UTF-8, the actual file name on
	disk would look like this:
      </para>

      <programlisting id="filename-utf-8">
Character:  P  r  e  s  e  n  t  a  c  i  &oacute;     n  .  s  x  i
Hex code:   50 72 65 73 65 6e 74 61 63 69 c3 b3 6e 2e 73 78 69
      </programlisting>

      <para>
	Glib uses UTF-8 for its strings, and GUI toolkits like GTK+
	that use Glib do the same thing.  If you get a file name from
	the file system, for example, from
	<function>readdir(3)</function> or from <link
	linkend="g_dir_read_name"><function>g_dir_read_name()</function></link>,
	and you wish to display the file name to the user, you
	<emphasis>will</emphasis> need to convert it into UTF-8.  The
	opposite case is when the user types the name of a file he
	wishes to save:  the toolkit will give you that string in
	UTF-8 encoding, and you will need to convert it to the
	character set used for file names before you can create the
	file with <function>open(2)</function> or
	<function>fopen(3)</function>.
      </para>

      <para>
	By default, Glib assumes that file names on disk are in UTF-8
	encoding.  This is a valid assumption for file systems which
	were created relatively recently:  most applications use UTF-8
	encoding for their strings, and that is also what they use for
	the file names they create.  However, older file systems may
	still contain file names created in "older" encodings, such as
	ISO-8859-1.  In this case, for compatibility reasons, you may
	want to instruct Glib to use that particular encoding for file
	names rather than UTF-8.  You can do this by specifying the
	encoding for file names in the <link
	linkend="G_FILENAME_ENCODING"><envar>G_FILENAME_ENCODING</envar></link>
	environment variable.  For example, if your installation uses
	ISO-8859-1 for file names, you can put this in your
	<filename>~/.profile</filename>:
      </para>

      <programlisting>
export G_FILENAME_ENCODING=ISO-8859-1
      </programlisting>

      <para>
	Glib provides the functions <link
	linkend="g_filename_to_utf8"><function>g_filename_to_utf8()</function></link>
	and <link
	linkend="g_filename_from_utf8"><function>g_filename_from_utf8()</function></link>
	to perform the necessary conversions.  These functions convert
	file names from the encoding specified in
	<envar>G_FILENAME_ENCODING</envar> to UTF-8 and vice-versa.
	<xref linkend="file-name-encodings-diagram"/> illustrates how
	these functions are used to convert between UTF-8 and the
	encoding for file names in the file system.
      </para>

      <figure id="file-name-encodings-diagram">
	<title>Conversion between File Name Encodings</title>
	<graphic fileref="file-name-encodings.png" format="PNG"/>
      </figure>

      <refsect3 id="file-name-encodings-checklist">
	<title>Checklist for Application Writers</title>

	<para>
	  This section is a practical summary of the detailed
	  description above.  You can use this as a checklist of
	  things to do to make sure your applications process file
	  name encodings correctly.
	</para>

	<orderedlist>
	  <listitem>
	    <para>
	      If you get a file name from the file system from a
	      function such as <function>readdir(3)</function> or
	      <function>gtk_file_chooser_get_filename()</function>,
	      you do not need to do any conversion to pass that
	      file name to functions like <function>open(2)</function>,
	      <function>rename(2)</function>, or
	      <function>fopen(3)</function> &mdash; those are "raw"
	      file names which the file system understands.
	    </para>
	  </listitem>

	  <listitem>
	    <para>
	      If you need to display a file name, convert it to UTF-8
	      first by using <link
	      linkend="g_filename_to_utf8"><function>g_filename_to_utf8()</function></link>.
	      If conversion fails, display a string like
	      "<literal>Unknown file name</literal>".  <emphasis>Do
	      not</emphasis> convert this string back into the
	      encoding used for file names if you wish to pass it to
	      the file system; use the original file name instead.
	      For example, the document window of a word processor
	      could display "Unknown file name" in its title bar but
	      still let the user save the file, as it would keep the
	      raw file name internally.  This can happen if the user
	      has not set the <envar>G_FILENAME_ENCODING</envar>
	      environment variable even though he has files whose
	      names are not encoded in UTF-8.
	    </para>
	  </listitem>

	  <listitem>
	    <para>
	      If your user interface lets the user type a file name
	      for saving or renaming, convert it to the encoding used
	      for file names in the file system by using <link
	      linkend="g_filename_from_utf8"><function>g_filename_from_utf8()</function></link>.
	      Pass the converted file name to functions like
	      <function>fopen(3)</function>.  If conversion fails, ask
	      the user to enter a different file name.  This can
	      happen if the user types Japanese characters when
	      <envar>G_FILENAME_ENCODING</envar> is set to
	      <literal>ISO-8859-1</literal>, for example.
	    </para>
	  </listitem>
	</orderedlist>
      </refsect3>
    </refsect2>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### FUNCTION g_convert ##### -->
<para>

</para>

@str:
@len:
@to_codeset:
@from_codeset:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### FUNCTION g_convert_with_fallback ##### -->
<para>

</para>

@str:
@len:
@to_codeset:
@from_codeset:
@fallback:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### STRUCT GIConv ##### -->
<para>
The <structname>GIConv</structname> struct wraps an
<function>iconv()</function> conversion descriptor. It contains private data
and should only be accessed using the following functions.
</para>


<!-- ##### FUNCTION g_convert_with_iconv ##### -->
<para>

</para>

@str:
@len:
@converter:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### MACRO G_CONVERT_ERROR ##### -->
<para>
Error domain for character set conversions. Errors in this domain will
be from the #GConvertError enumeration. See #GError for information on
error domains.
</para>


<!-- ##### FUNCTION g_iconv_open ##### -->
<para>

</para>

@to_codeset:
@from_codeset:
@Returns:


<!-- ##### FUNCTION g_iconv ##### -->
<para>

</para>

@converter:
@inbuf:
@inbytes_left:
@outbuf:
@outbytes_left:
@Returns:


<!-- ##### FUNCTION g_iconv_close ##### -->
<para>

</para>

@converter:
@Returns:


<!-- ##### FUNCTION g_locale_to_utf8 ##### -->
<para>

</para>

@opsysstring:
@len:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### FUNCTION g_filename_to_utf8 ##### -->
<para>

</para>

@opsysstring:
@len:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### FUNCTION g_filename_from_utf8 ##### -->
<para>

</para>

@utf8string:
@len:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### FUNCTION g_filename_from_uri ##### -->
<para>

</para>

@uri:
@hostname:
@error:
@Returns:


<!-- ##### FUNCTION g_filename_to_uri ##### -->
<para>

</para>

@filename:
@hostname:
@error:
@Returns:


<!-- ##### FUNCTION g_get_filename_charsets ##### -->
<para>

</para>

@charsets:
@Returns:


<!-- ##### FUNCTION g_filename_display_name ##### -->
<para>

</para>

@filename:
@Returns:


<!-- ##### FUNCTION g_filename_display_basename ##### -->
<para>

</para>

@filename:
@Returns:


<!-- ##### FUNCTION g_uri_list_extract_uris ##### -->
<para>

</para>

@uri_list:
@Returns:


<!-- ##### FUNCTION g_locale_from_utf8 ##### -->
<para>

</para>

@utf8string:
@len:
@bytes_read:
@bytes_written:
@error:
@Returns:


<!-- ##### ENUM GConvertError ##### -->
<para>
Error codes returned by character set conversion routines.
</para>

@G_CONVERT_ERROR_NO_CONVERSION: Conversion between the requested character sets
is not supported.
@G_CONVERT_ERROR_ILLEGAL_SEQUENCE: Invalid byte sequence in conversion input.
@G_CONVERT_ERROR_FAILED: Conversion failed for some reason.
@G_CONVERT_ERROR_PARTIAL_INPUT: Partial character sequence at end of input.
@G_CONVERT_ERROR_BAD_URI: URI is invalid.
@G_CONVERT_ERROR_NOT_ABSOLUTE_PATH: Pathname is not an absolute path.

<!-- ##### FUNCTION g_get_charset ##### -->
<para>

</para>

@charset:
@Returns:


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