<li><a href="#Error_treatment">Error treatment</a></li>
<li><a href="#Compatibility_mode">Compatibility mode</a></li>
- </ul>
+ </ul><li><a href="#Converting_character_sets">Converting character sets</a><br>
+ </li>
+
<li><a href="interface.html">Interface details</a><br>
</li>
<blockquote><code>Error on line</code> <i><lineno></i>: <i><actual_message></i><br>
</blockquote>
Note that the entire string will be properly internationalized, and
-encoded in UTF-8 (see "Why UTF-8?" <i>LINK TBD</i>). Also,
+encoded in UTF-8 (<a href="encoding.html">Why UTF-8?</a>). Also,
no newline is appended, so that the application program can use it in any
way it wants. Warnings are similar, but use "Warning" instead of
"Error". Messages are plain text, without any prefix.<br>
</ul>
Note that, currently, no actual compatibility code is present, but this
is on the to-do list.<br>
+ <hr width="100%" size="2">
+ <h2><a name="Converting_character_sets"></a>Converting character sets</h2>
+All strings passed by the GEDCOM parser to the application are in UTF-8 encoding.
+ Typically, an application needs to convert this to something else to
+be able to display it.<br>
+ <br>
+The most common case is that the output character set is controlled by the <code>locale</code> mechanism (i.e. via the <code>LANG</code>, <code>LC_ALL</code> or <code>LC_CTYPE</code> environment variables), which also controls the <code>gettext</code>
+ mechanism in the application. For this, the following steps need to
+be taken by the application (more detailed info can be found in the info
+file of the GNU libc library in the "Generic Charset Conversion" section
+under "Character Set Handling" or online <a href="http://www.gnu.org/manual/glibc-2.2.3/html_chapter/libc_6.html#SEC99">here</a>):<br>
+ <ul>
+ <li>inclusion of some headers:</li>
+ </ul>
+ <blockquote>
+ <blockquote>
+ <pre><code>#include <locale.h> /* for setlocale */<br>#include <langinfo.h> /* for nl_langinfo */<br>#include <iconv.h> /* for iconv_* functions */<br></code></pre>
+ </blockquote>
+ </blockquote>
+ <ul>
+ <li>set the program's current locale to what the user configured in the environment:</li>
+ </ul>
+ <blockquote>
+ <blockquote>
+ <pre><code>setlocale(LC_ALL, "");</code><br></pre>
+ </blockquote>
+ </blockquote>
+ <ul>
+ <li>open a conversion handle for conversion from UTF-8 to the character set of the current locale (once for the entire program):</li>
+ </ul>
+ <blockquote>
+ <blockquote>
+ <pre><code>iconv_t iconv_handle;<br>...<br>iconv_handle = iconv_open(nl_langinfo(CODESET), "UTF-8");</code><br>if (iconv_handle == (iconv_t) -1)<br> /* signal an error */<br></pre>
+ </blockquote>
+ </blockquote>
+ <ul>
+ <li>then, every string can be converted using the following:</li>
+ </ul>
+ <blockquote>
+ <blockquote>
+ <pre><code>/* char* in_buf is the input buffer, size_t in_len is its length */<br>/* char* out_buf is the output buffer, size_t out_len is its length */<br><br>size_t nconv;<br>char *in_ptr = in_buf;<br>char *out_ptr = out_buf;<br>nconv = iconv(iconv_handle, &in_ptr, &in_len, &out_ptr, &out_len);</code></pre>
+ </blockquote>
+ </blockquote>
+ <blockquote>If the output buffer is not big enough, <code>iconv</code> will return -1 and set <code>errno</code> to <code>E2BIG</code>. Also, the <code>in_ptr</code> and <code>out_ptr</code> will point just after the last successfully converted character in the respective buffers, and the <code>in_len</code> and <code>out_len</code> will be updated to show the remaining lengths. There can be two strategies here:<br>
+ <ul>
+ <li>Make sure from the beginning
+that the output buffer is big enough. However, it's difficult to find
+an absolute maximum length in advance, even given the length of the input
+string.<br>
+ <br>
+ </li>
+ <li>Do the conversion in several steps, growing the output buffer each time to make more space, and calling <code>iconv</code>
+ consecutively until the conversion is complete. This is the preferred
+way (a function could be written to encapsulate all this).</li>
+ </ul>
+Another error case is when the conversion was unsuccessful (if one of the
+characters can't be represented in the target character set). The <code>iconv</code> function will then also return -1 and set <code>errno</code> to <code>EILSEQ</code>; the <code>in_ptr</code> will point to the character that couldn't be converted. In that case, again two strategies are possible:<br>
+ <ul>
+ <li>Just fail the conversion, and show an error. This is not very user friendly, of course.<br>
+ <br>
+ </li>
+ <li>Skip over the character that can't be converted and append a "?" to the output buffer, then call <code>iconv</code> again. Skipping over a UTF-8 character is fairly simple, as follows from the <a href="http://www.cl.cam.ac.uk/%7Emgk25/unicode.html#utf-8">encoding rules</a>:</li>
+ </ul>
+ <ol>
+ <ol>
+ <li>if the first byte is in binary 0xxxxxxx, then the character is only one byte long, just skip over that byte<br>
+ <br>
+ </li>
+ <li>if the first byte is in binary 11xxxxxx, then skip over that byte and all bytes 10xxxxxx that follow.<br>
+ </li>
+ </ol>
+ </ol>
+ </blockquote>
+ <ul>
+ <li>eventually, the conversion handle needs to be closed (when the program exits):<br>
+ </li>
+ </ul>
+ <blockquote>
+ <blockquote>
+ <pre><code>iconv_close(iconv_handle);<br></code></pre>
+ </blockquote>
+ </blockquote>
+
- <hr width="100%" size="2">
+ The source distribution of <code>gedcom-parse</code> contains an example implementation (<code>utf8-locale.c</code> and <code>utf8-locale.h</code>
+ in the top directory) that grows the output buffer dynamically and outputs
+"?" for characters that can't be converted. Feel free to use it in
+your source code (it is not part of the library, and it isn't installed anywhere,
+so you need to take over the source and header file in your application).
+ <br>
+ <br>
+Its interface is:<br>
+ <blockquote>
+ <pre><code>char *<b>convert_utf8_to_locale</b> (char *input);<br>char *<b>convert_locale_to_utf8</b> (char *input);<br></code></pre>
+ </blockquote>
+Both functions return a pointer to a static buffer that is overwritten on
+each call. To function properly, the application must first set the
+locale using the <code>setlocale</code> function (the second step above).
+ All other steps, including setting up and closing down the conversion
+handles, are transparantly handled by the two functions.<br>
+ <br>
+You can change the "?" that is output for characters that can't be converted
+to any string you want, using the following function before the conversion
+calls:<br>
+ <blockquote>
+ <pre><code>void <b>convert_set_unknown</b> (const char *unknown);</code></pre>
+ </blockquote>
+ <hr width="100%" size="2">
<pre><font size="-1">$Id$<br>$Name$</font><br></pre>
projects / gedcom-parse.git / blobdiff