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<h1 class="chapter"> <a href="libunistring_toc.html#TOC54">10. Grapheme cluster breaks in strings <code><unigbrk.h></code></a> </h1>
<p>This include file declares functions for determining where in a string
“grapheme clusters” start and end. A “grapheme cluster” is an
approximation to a user-perceived character, which sometimes
corresponds to multiple Unicode characters. Editing operations such as
mouse selection, cursor movement, and backspacing often operate on
grapheme clusters as units, not on individual characters.
</p>
<p>Some grapheme clusters are built from a base character and a combining
character. The letter ‘<samp>é</samp>’,
for example, is most commonly represented in Unicode as a single
character U+00E8 <small>LATIN SMALL LETTER E WITH ACUTE</small>. It is,
however, equally valid to use the pair of characters U+0065 <small>LATIN
SMALL LETTER E</small> followed by U+0301 <small>COMBINING ACUTE ACCENT</small>. Since
the user would perceive this pair of characters as a single character,
they would be grouped into a single grapheme cluster.
</p>
<p>But there are also grapheme clusters that consist of several base characters.
For example, a Devanagari letter and a Devanagari vowel sign that follows it
may form a grapheme cluster. Similarly, some pairs of Thai characters and
Hangul syllables (formed by two or three Hangul characters) are grapheme
clusters.
</p>
<hr size="6">
<a name="Grapheme-cluster-breaks-in-a-string"></a>
<a name="SEC55"></a>
<h2 class="section"> <a href="libunistring_toc.html#TOC55">10.1 Grapheme cluster breaks in a string</a> </h2>
<p>The following functions find a single boundary between grapheme
clusters in a string.
</p>
<dl>
<dt><u>Function:</u> void <b>u8_grapheme_next</b><i> (const uint8_t *<var>s</var>, const uint8_t *<var>end</var>)</i>
<a name="IDX769"></a>
</dt>
<dt><u>Function:</u> void <b>u16_grapheme_next</b><i> (const uint16_t *<var>s</var>, const uint16_t *<var>end</var>)</i>
<a name="IDX770"></a>
</dt>
<dt><u>Function:</u> void <b>u32_grapheme_next</b><i> (const uint32_t *<var>s</var>, const uint32_t *<var>end</var>)</i>
<a name="IDX771"></a>
</dt>
<dd><p>Returns the start of the next grapheme cluster following <var>s</var>,
or <var>end</var> if no grapheme cluster break is encountered before it.
Returns NULL if and only if <code><var>s</var> == <var>end</var></code>.
</p>
<p>Note that these functions do not handle the case when a character
outside of the range between <var>s</var> and <var>end</var> is needed to
determine the boundary. Use <code>_grapheme_breaks</code> functions for such
cases.
</p></dd></dl>
<dl>
<dt><u>Function:</u> void <b>u8_grapheme_prev</b><i> (const uint8_t *<var>s</var>, const uint8_t *<var>start</var>)</i>
<a name="IDX772"></a>
</dt>
<dt><u>Function:</u> void <b>u16_grapheme_prev</b><i> (const uint16_t *<var>s</var>, const uint16_t *<var>start</var>)</i>
<a name="IDX773"></a>
</dt>
<dt><u>Function:</u> void <b>u32_grapheme_prev</b><i> (const uint32_t *<var>s</var>, const uint32_t *<var>start</var>)</i>
<a name="IDX774"></a>
</dt>
<dd><p>Returns the start of the grapheme cluster preceding <var>s</var>, or
<var>start</var> if no grapheme cluster break is encountered before it.
Returns NULL if and only if <code><var>s</var> == <var>start</var></code>.
</p>
<p>Note that these functions do not handle the case when a character
outside of the range between <var>start</var> and <var>s</var> is needed to
determine the boundary. Use <code>_grapheme_breaks</code> functions for such
cases.
</p>
<p>Note also that these functions work only on well-formed Unicode strings.
</p></dd></dl>
<p>The following functions determine all of the grapheme cluster
boundaries in a string.
</p>
<dl>
<dt><u>Function:</u> void <b>u8_grapheme_breaks</b><i> (const uint8_t *<var>s</var>, size_t <var>n</var>, char *<var>p</var>)</i>
<a name="IDX775"></a>
</dt>
<dt><u>Function:</u> void <b>u16_grapheme_breaks</b><i> (const uint16_t *<var>s</var>, size_t <var>n</var>, char *<var>p</var>)</i>
<a name="IDX776"></a>
</dt>
<dt><u>Function:</u> void <b>u32_grapheme_breaks</b><i> (const uint32_t *<var>s</var>, size_t <var>n</var>, char *<var>p</var>)</i>
<a name="IDX777"></a>
</dt>
<dt><u>Function:</u> void <b>ulc_grapheme_breaks</b><i> (const char *<var>s</var>, size_t <var>n</var>, char *<var>p</var>)</i>
<a name="IDX778"></a>
</dt>
<dt><u>Function:</u> void <b>uc_grapheme_breaks</b><i> (const ucs_t *<var>s</var>, size_t <var>n</var>, char *<var>p</var>)</i>
<a name="IDX779"></a>
</dt>
<dd><p>Determines the grapheme cluster break points in <var>s</var>, an array of
<var>n</var> units, and stores the result at <code><var>p</var>[0..<var>nx</var>-1]</code>.
</p><dl compact="compact">
<dt> <code><var>p</var>[i] = 1</code></dt>
<dd><p>means that there is a grapheme cluster boundary between
<code><var>s</var>[i-1]</code> and <code><var>s</var>[i]</code>.
</p></dd>
<dt> <code><var>p</var>[i] = 0</code></dt>
<dd><p>means that <code><var>s</var>[i-1]</code> and <code><var>s</var>[i]</code> are part of the
same grapheme cluster.
</p></dd>
</dl>
<p><code><var>p</var>[0]</code> is always set to 1, because there is always a
grapheme cluster break at start of text.
</p>
<p>In addition to the above variants for UTF-8, UTF-16, and UTF-32 strings,
<code><unigbrk.h></code> provides another variant: <code>uc_grapheme_breaks</code>.
</p>
<p>This is similar to <code>u32_grapheme_breaks</code>, but it accepts any
characters which may not be represented in UTF-32, such as control
characters.
</p></dd></dl>
<hr size="6">
<a name="Grapheme-cluster-break-property"></a>
<a name="SEC56"></a>
<h2 class="section"> <a href="libunistring_toc.html#TOC56">10.2 Grapheme cluster break property</a> </h2>
<p>This is a more low-level API. The grapheme cluster break property is a
property defined in Unicode Standard Annex #29, section “Grapheme Cluster
Boundaries”, see
<a href="https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries">https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries</a>.
It is used for determining the grapheme cluster breaks in a string.
</p>
<p>The following are the possible values of the grapheme cluster break
property. More values may be added in the future.
</p>
<dl>
<dt><u>Constant:</u> int <b>GBP_OTHER</b>
<a name="IDX780"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_CR</b>
<a name="IDX781"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_LF</b>
<a name="IDX782"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_CONTROL</b>
<a name="IDX783"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_EXTEND</b>
<a name="IDX784"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_PREPEND</b>
<a name="IDX785"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_SPACINGMARK</b>
<a name="IDX786"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_L</b>
<a name="IDX787"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_V</b>
<a name="IDX788"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_T</b>
<a name="IDX789"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_LV</b>
<a name="IDX790"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_LVT</b>
<a name="IDX791"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_RI</b>
<a name="IDX792"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_ZWJ</b>
<a name="IDX793"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_EB</b>
<a name="IDX794"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_EM</b>
<a name="IDX795"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_GAZ</b>
<a name="IDX796"></a>
</dt>
<dt><u>Constant:</u> int <b>GBP_EBG</b>
<a name="IDX797"></a>
</dt>
</dl>
<p>The following function looks up the grapheme cluster break property of a
character.
</p>
<dl>
<dt><u>Function:</u> int <b>uc_graphemeclusterbreak_property</b><i> (ucs4_t <var>uc</var>)</i>
<a name="IDX798"></a>
</dt>
<dd><p>Returns the Grapheme_Cluster_Break property of a Unicode character.
</p></dd></dl>
<p>The following function determines whether there is a grapheme cluster
break between two Unicode characters. It is the primitive upon which
the higher-level functions in the previous section are directly based.
</p>
<dl>
<dt><u>Function:</u> bool <b>uc_is_grapheme_break</b><i> (ucs4_t <var>a</var>, ucs4_t <var>b</var>)</i>
<a name="IDX799"></a>
</dt>
<dd><p>Returns true if there is an grapheme cluster boundary between Unicode
characters <var>a</var> and <var>b</var>.
</p>
<p>There is always a grapheme cluster break at the start or end of text.
You can specify zero for <var>a</var> or <var>b</var> to indicate start of text or end
of text, respectively.
</p>
<p>This implements the extended (not legacy) grapheme cluster rules
described in the Unicode standard, because the standard says that they
are preferred.
</p>
<p>Note that this function does not handle the case when three or more
consecutive characters are needed to determine the boundary. Use
<code>uc_grapheme_breaks</code> for such cases.
</p></dd></dl>
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