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120 lines
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<q>...one of the most highly
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<span class="heading-attribution">— <a href=
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<li><a class="el" href="main.html">Boost.Locale</a> </li>
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<div class="header">
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<h1>Text Conversions </h1> </div>
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<div class="contents">
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<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#ga7889a57e1bc1059fbb107db0781d0b6d">to_upper</a> , <a class="el" href="group__convert.html#ga33de83f16ff2c09cac780977c6f67099">to_lower</a>, <a class="el" href="group__convert.html#ga646f42adb01baf395d632c32f556a5b9">to_title</a>, <a class="el" href="group__convert.html#gabd1bc157122a5b9392487126fd0fffe5">fold_case</a> and <a class="el" href="group__convert.html#ga11672e3cc3ed7eecf1dd07060265aab2">normalize</a>.</p>
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<p>All these functions receive an <code>std::locale</code> object as parameter or use a global locale by default.</p>
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<p>Global locale is used in all examples below.</p>
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<h2><a class="anchor" id="conversions_case"></a>
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Case Handing</h2>
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<p>For example: </p>
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<div class="fragment"><pre class="fragment"> std::string grussen = <span class="stringliteral">"grüßEN"</span>;
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std::cout <<<span class="stringliteral">"Upper "</span><< <a class="code" href="group__convert.html#ga7889a57e1bc1059fbb107db0781d0b6d">boost::locale::to_upper</a>(grussen) << std::endl
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<<<span class="stringliteral">"Lower "</span><< <a class="code" href="group__convert.html#ga33de83f16ff2c09cac780977c6f67099">boost::locale::to_lower</a>(grussen) << std::endl
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<<<span class="stringliteral">"Title "</span><< <a class="code" href="group__convert.html#ga646f42adb01baf395d632c32f556a5b9">boost::locale::to_title</a>(grussen) << std::endl
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<<<span class="stringliteral">"Fold "</span><< <a class="code" href="group__convert.html#gabd1bc157122a5b9392487126fd0fffe5">boost::locale::fold_case</a>(grussen) << std::endl;
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</pre></div><p>Would print:</p>
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<div class="fragment"><pre class="fragment">
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Upper GRÜSSEN
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Lower grüßen
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Title Grüßen
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Fold grüssen
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</pre></div><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>
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<p>For example:</p>
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<div class="fragment"><pre class="fragment"> std::wstring grussen = L<span class="stringliteral">"grüßen"</span>;
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std::wcout << boost::algorithm::to_upper_copy(grussen) << <span class="stringliteral">" "</span> << <a class="code" href="group__convert.html#ga7889a57e1bc1059fbb107db0781d0b6d">boost::locale::to_upper</a>(grussen) << std::endl;
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</pre></div><p>Would give in output:</p>
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<div class="fragment"><pre class="fragment">
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GRÜßEN GRÜSSEN
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</pre></div><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>
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<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>
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<div class="fragment"><pre class="fragment"> std::string grussen = <span class="stringliteral">"grüßen"</span>;
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std::cout << boost::algorithm::to_upper_copy(grussen) << <span class="stringliteral">" "</span> << <a class="code" href="group__convert.html#ga7889a57e1bc1059fbb107db0781d0b6d">boost::locale::to_upper</a>(grussen) << std::endl;
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</pre></div><p>Would modify ASCII characters only</p>
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<div class="fragment"><pre class="fragment">
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GRüßEN GRÜSSEN
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</pre></div><h2><a class="anchor" id="conversions_normalization"></a>
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Unicode Normalization</h2>
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<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>
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<p>Unicode defines four normalization forms. Each specific form is selected by a flag passed to <a class="el" href="group__convert.html#ga11672e3cc3ed7eecf1dd07060265aab2">normalize</a> function:</p>
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<ul>
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<li>NFD - Canonical decomposition - boost::locale::norm_nfd</li>
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<li>NFC - Canonical decomposition followed by canonical composition - boost::locale::norm_nfc or boost::locale::norm_default</li>
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<li>NFKD - Compatibility decomposition - boost::locale::norm_nfkd</li>
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<li>NFKC - Compatibility decomposition followed by canonical composition - boost::locale::norm_nfkc</li>
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</ul>
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<p>For more details on normalization forms, read <a href="http://unicode.org/reports/tr15/#Norm_Forms">this article</a>.</p>
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<h2><a class="anchor" id="conversions_notes"></a>
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Notes</h2>
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<ul>
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<li><a class="el" href="group__convert.html#ga11672e3cc3ed7eecf1dd07060265aab2">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>
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<li><a class="el" href="group__convert.html#gabd1bc157122a5b9392487126fd0fffe5">fold_case</a> is generally a locale-independent operation, but it receives a locale as a parameter to determine the 8-bit encoding.</li>
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<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>
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<li>The length of the string may change, see the above example. </li>
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