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<div class="title">Text Conversions </div>  </div>
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<div class="textblock"><p>There is a set of functions that perform basic string conversion operations: upper, lower and <a class="el" href="glossary.html#term_title_case">title case</a> conversions, <a class="el" href="glossary.html#term_case_folding">case folding</a> and Unicode <a class="el" href="glossary.html#term_normalization">normalization</a>. These are <a class="el" href="group__convert.html#ga2ceae621801e8cf4f77c60d1e3047ae8">to_upper</a> , <a class="el" href="group__convert.html#ga4a3eb15f42f5cbae7bdd00c9e9cac222">to_lower</a>, <a class="el" href="group__convert.html#ga684efb375e060c71cd3e1799a6329f7f">to_title</a>, <a class="el" href="group__convert.html#gadf59d16355babd955766deef89d470ea">fold_case</a> and <a class="el" href="group__convert.html#ga867733c9d4455aaa13a42cf67367d575">normalize</a>.</p>
<p>All these functions receive an <code>std::locale</code> object as parameter or use a global locale by default.</p>
<p>Global locale is used in all examples below.</p>
<h1><a class="anchor" id="conversions_case"></a>
Case Handing</h1>
<p>For example: </p>
<div class="fragment"><div class="line">std::string grussen = <span class="stringliteral">&quot;grüßEN&quot;</span>;</div>
<div class="line">std::cout   &lt;&lt;<span class="stringliteral">&quot;Upper &quot;</span>&lt;&lt; <a class="code" href="group__convert.html#ga2ceae621801e8cf4f77c60d1e3047ae8">boost::locale::to_upper</a>(grussen) &lt;&lt; std::endl</div>
<div class="line">            &lt;&lt;<span class="stringliteral">&quot;Lower &quot;</span>&lt;&lt; <a class="code" href="group__convert.html#ga4a3eb15f42f5cbae7bdd00c9e9cac222">boost::locale::to_lower</a>(grussen) &lt;&lt; std::endl</div>
<div class="line">            &lt;&lt;<span class="stringliteral">&quot;Title &quot;</span>&lt;&lt; <a class="code" href="group__convert.html#ga684efb375e060c71cd3e1799a6329f7f">boost::locale::to_title</a>(grussen) &lt;&lt; std::endl</div>
<div class="line">            &lt;&lt;<span class="stringliteral">&quot;Fold  &quot;</span>&lt;&lt; <a class="code" href="group__convert.html#gadf59d16355babd955766deef89d470ea">boost::locale::fold_case</a>(grussen) &lt;&lt; std::endl;</div>
</div><!-- fragment --><p>Would print:</p>
<pre class="fragment">Upper GRÜSSEN
Lower grüßen
Title Grüßen
Fold  grüssen
</pre><p>You may notice that there are existing functions <code>to_upper</code> and <code>to_lower</code> in the Boost.StringAlgo library. The difference is that these function operate over an entire string instead of performing incorrect character-by-character conversions.</p>
<p>For example:</p>
<div class="fragment"><div class="line">std::wstring grussen = L<span class="stringliteral">&quot;grüßen&quot;</span>;</div>
<div class="line">std::wcout &lt;&lt; boost::algorithm::to_upper_copy(grussen) &lt;&lt; <span class="stringliteral">&quot; &quot;</span> &lt;&lt; <a class="code" href="group__convert.html#ga2ceae621801e8cf4f77c60d1e3047ae8">boost::locale::to_upper</a>(grussen) &lt;&lt; std::endl;</div>
</div><!-- fragment --><p>Would give in output:</p>
<pre class="fragment">GRÜßEN GRÜSSEN
</pre><p>Where a letter "ß" was not converted correctly to double-S in first case because of a limitation of <code>std::ctype</code> facet.</p>
<p>This is even more problematic in case of UTF-8 encodings where non US-ASCII are not converted at all. For example, this code</p>
<div class="fragment"><div class="line">std::string grussen = <span class="stringliteral">&quot;grüßen&quot;</span>;</div>
<div class="line">std::cout &lt;&lt; boost::algorithm::to_upper_copy(grussen) &lt;&lt; <span class="stringliteral">&quot; &quot;</span> &lt;&lt; <a class="code" href="group__convert.html#ga2ceae621801e8cf4f77c60d1e3047ae8">boost::locale::to_upper</a>(grussen) &lt;&lt; std::endl;</div>
</div><!-- fragment --><p>Would modify ASCII characters only</p>
<pre class="fragment">GRüßEN GRÜSSEN
</pre><h1><a class="anchor" id="conversions_normalization"></a>
Unicode Normalization</h1>
<p>Unicode normalization is the process of converting strings to a standard form, suitable for text processing and comparison. For example, character "ü" can be represented by a single code point or a combination of the character "u" and the diaeresis "¨". Normalization is an important part of Unicode text processing.</p>
<p>Unicode defines four normalization forms. Each specific form is selected by a flag passed to <a class="el" href="group__convert.html#ga867733c9d4455aaa13a42cf67367d575">normalize</a> function:</p>
<ul>
<li>NFD - Canonical decomposition - <a class="el" href="group__convert.html#gga6a595a415b83b8a0c8f14c34eb66cc9fa6648d0eabb931f2e9d258570b297e98f" title="Canonical decomposition. ">boost::locale::norm_nfd</a></li>
<li>NFC - Canonical decomposition followed by canonical composition - <a class="el" href="group__convert.html#gga6a595a415b83b8a0c8f14c34eb66cc9faf6fe7be275e5e13df415ab258105ada0" title="Canonical decomposition followed by canonical composition. ">boost::locale::norm_nfc</a> or <a class="el" href="group__convert.html#gga6a595a415b83b8a0c8f14c34eb66cc9faa29173d73d9be7fefcbb18c8712465d2" title="Default normalization - canonical decomposition followed by canonical composition. ">boost::locale::norm_default</a></li>
<li>NFKD - Compatibility decomposition - <a class="el" href="group__convert.html#gga6a595a415b83b8a0c8f14c34eb66cc9fa0fbc2ac042fc6f58af5818bfd06d5379" title="Compatibility decomposition. ">boost::locale::norm_nfkd</a></li>
<li>NFKC - Compatibility decomposition followed by canonical composition - <a class="el" href="group__convert.html#gga6a595a415b83b8a0c8f14c34eb66cc9fa0305c1f3405ea70facf4c6a5ffa40583" title="Compatibility decomposition followed by canonical composition. ">boost::locale::norm_nfkc</a></li>
</ul>
<p>For more details on normalization forms, read <a href="http://unicode.org/reports/tr15/#Norm_Forms">this article</a>.</p>
<h1><a class="anchor" id="conversions_notes"></a>
Notes</h1>
<ul>
<li><a class="el" href="group__convert.html#ga867733c9d4455aaa13a42cf67367d575">normalize</a> operates only on Unicode-encoded strings, i.e.: UTF-8, UTF-16 and UTF-32 depending on the character width. So be careful when using non-UTF encodings as they may be treated incorrectly.</li>
<li><a class="el" href="group__convert.html#gadf59d16355babd955766deef89d470ea">fold_case</a> is generally a locale-independent operation, but it receives a locale as a parameter to determine the 8-bit encoding.</li>
<li>All of these functions can work with an STL string, a NUL terminated string, or a range defined by two pointers. They always return a newly created STL string.</li>
<li>The length of the string may change, see the above example. </li>
</ul>
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