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+ "A simple, portable and lightweigt C++ library for easy handling of UTF-8 encoded strings">
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+ <meta name="author" content="Nemanja Trifunovic">
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+ UTF8-CPP: UTF-8 with C++ in a Portable Way
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+ <h1>
+ UTF8-CPP: UTF-8 with C++ in a Portable Way
+ </h1>
+ <p>
+ <a href="https://sourceforge.net/projects/utfcpp">The Sourceforge project page</a>
+ </p>
+ <div id="toc">
+ <h2>
+ Table of Contents
+ </h2>
+ <ul class="toc">
+ <li>
+ <a href="#introduction">Introduction</a>
+ </li>
+ <li>
+ <a href="#examples">Examples of Use</a>
+ <ul class="toc">
+ <li>
+ <a href=#introsample>Introductionary Sample </a>
+ </li>
+ <li>
+ <a href=#validfile>Checking if a file contains valid UTF-8 text</a>
+ </li>
+ <li>
+ <a href=#fixinvalid>Ensure that a string contains valid UTF-8 text</a>
+ </li>
+ </ul>
+ <li>
+ <a href="#reference">Reference</a>
+ <ul class="toc">
+ <li>
+ <a href="#funutf8">Functions From utf8 Namespace </a>
+ </li>
+ <li>
+ <a href="#typesutf8">Types From utf8 Namespace </a>
+ </li>
+ <li>
+ <a href="#fununchecked">Functions From utf8::unchecked Namespace </a>
+ </li>
+ <li>
+ <a href="#typesunchecked">Types From utf8::unchecked Namespace </a>
+ </li>
+ </ul>
+ </li>
+ <li>
+ <a href="#points">Points of Interest</a>
+ </li>
+ <li>
+ <a href="#links">Links</a>
+ </li>
+ </ul>
+ </div>
+ <h2 id="introduction">
+ Introduction
+ </h2>
+ <p>
+ Many C++ developers miss an easy and portable way of handling Unicode encoded
+ strings. The original C++ Standard (known as C++98 or C++03) is Unicode agnostic.
+ C++11 provides some support for Unicode on core language and library level:
+ u8, u, and U character and string literals, char16_t and char32_t character types,
+ u16string and u32string library classes, and codecvt support for conversions
+ between Unicode encoding forms.
+ In the meantime, developers use third party libraries like ICU, OS specific capabilities, or simply
+ roll out their own solutions.
+ </p>
+ <p>
+ In order to easily handle UTF-8 encoded Unicode strings, I came up with a small
+ generic library. For anybody used to work with STL algorithms and iterators, it should be
+ easy and natural to use. The code is freely available for any purpose - check out
+ the license at the beginning of the utf8.h file. If you run into
+ bugs or performance issues, please let me know and I'll do my best to address them.
+ </p>
+ <p>
+ The purpose of this article is not to offer an introduction to Unicode in general,
+ and UTF-8 in particular. If you are not familiar with Unicode, be sure to check out
+ <a href="http://www.unicode.org/">Unicode Home Page</a> or some other source of
+ information for Unicode. Also, it is not my aim to advocate the use of UTF-8
+ encoded strings in C++ programs; if you want to handle UTF-8 encoded strings from
+ C++, I am sure you have good reasons for it.
+ </p>
+ <h2 id="examples">
+ Examples of use
+ </h2>
+ <h3 id="introsample">
+ Introductionary Sample
+ </h3>
+ <p>
+ To illustrate the use of the library, let's start with a small but complete program
+ that opens a file containing UTF-8 encoded text, reads it line by line, checks each line
+ for invalid UTF-8 byte sequences, and converts it to UTF-16 encoding and back to UTF-8:
+ </p>
+<pre>
+<span class="preprocessor">#include <fstream></span>
+<span class="preprocessor">#include <iostream></span>
+<span class="preprocessor">#include <string></span>
+<span class="preprocessor">#include <vector></span>
+<span class="preprocessor">#include "utf8.h"</span>
+<span class="keyword">using namespace</span> std;
+<span class="keyword">int</span> main(<span class="keyword">int</span> argc, <span class="keyword">char</span>** argv)
+{
+ <span class="keyword">if</span> (argc != <span class="literal">2</span>) {
+ cout << <span class="literal">"\nUsage: docsample filename\n"</span>;
+ <span class="keyword">return</span> <span class="literal">0</span>;
+ }
+
+ <span class="keyword">const char</span>* test_file_path = argv[1];
+ <span class="comment">// Open the test file (contains UTF-8 encoded text)</span>
+ ifstream fs8(test_file_path);
+ <span class="keyword">if</span> (!fs8.is_open()) {
+ cout << <span class=
+"literal">"Could not open "</span> << test_file_path << endl;
+ <span class="keyword">return</span> <span class="literal">0</span>;
+ }
+
+ <span class="keyword">unsigned</span> line_count = <span class="literal">1</span>;
+ string line;
+ <span class="comment">// Play with all the lines in the file</span>
+ <span class="keyword">while</span> (getline(fs8, line)) {
+ <span class="comment">// check for invalid utf-8 (for a simple yes/no check, there is also utf8::is_valid function)</span>
+ string::iterator end_it = utf8::find_invalid(line.begin(), line.end());
+ <span class="keyword">if</span> (end_it != line.end()) {
+ cout << <span class=
+"literal">"Invalid UTF-8 encoding detected at line "</span> << line_count << <span
+ class="literal">"\n"</span>;
+ cout << <span class=
+"literal">"This part is fine: "</span> << string(line.begin(), end_it) << <span
+ class="literal">"\n"</span>;
+ }
+
+ <span class="comment">// Get the line length (at least for the valid part)</span>
+ <span class="keyword">int</span> length = utf8::distance(line.begin(), end_it);
+ cout << <span class=
+"literal">"Length of line "</span> << line_count << <span class=
+"literal">" is "</span> << length << <span class="literal">"\n"</span>;
+
+ <span class="comment">// Convert it to utf-16</span>
+ vector<unsigned short> utf16line;
+ utf8::utf8to16(line.begin(), end_it, back_inserter(utf16line));
+
+ <span class="comment">// And back to utf-8</span>
+ string utf8line;
+ utf8::utf16to8(utf16line.begin(), utf16line.end(), back_inserter(utf8line));
+
+ <span class="comment">// Confirm that the conversion went OK:</span>
+ <span class="keyword">if</span> (utf8line != string(line.begin(), end_it))
+ cout << <span class=
+"literal">"Error in UTF-16 conversion at line: "</span> << line_count << <span
+ class="literal">"\n"</span>;
+
+ line_count++;
+ }
+ <span class="keyword">return</span> <span class="literal">0</span>;
+}
+</pre>
+ <p>
+ In the previous code sample, for each line we performed
+ a detection of invalid UTF-8 sequences with <code>find_invalid</code>; the number
+ of characters (more precisely - the number of Unicode code points, including the end
+ of line and even BOM if there is one) in each line was
+ determined with a use of <code>utf8::distance</code>; finally, we have converted
+ each line to UTF-16 encoding with <code>utf8to16</code> and back to UTF-8 with
+ <code>utf16to8</code>.
+ </p>
+ <h3 id="validfile">Checking if a file contains valid UTF-8 text</h3>
+<p>
+Here is a function that checks whether the content of a file is valid UTF-8 encoded text without
+reading the content into the memory:
+</p>
+<pre>
+<span class="keyword">bool</span> valid_utf8_file(i<span class="keyword">const char</span>* file_name)
+{
+ ifstream ifs(file_name);
+ <span class="keyword">if</span> (!ifs)
+ <span class="keyword">return false</span>; <span class="comment">// even better, throw here</span>
+
+ istreambuf_iterator<<span class="keyword">char</span>> it(ifs.rdbuf());
+ istreambuf_iterator<<span class="keyword">char</span>> eos;
+
+ <span class="keyword">return</span> utf8::is_valid(it, eos);
+}
+</pre>
+<p>
+Because the function <code>utf8::is_valid()</code> works with input iterators, we were able
+to pass an <code>istreambuf_iterator</code> to it and read the content of the file directly
+without loading it to the memory first.</p>
+<p>
+Note that other functions that take input iterator arguments can be used in a similar way. For
+instance, to read the content of a UTF-8 encoded text file and convert the text to UTF-16, just
+do something like:
+</p>
+<pre>
+ utf8::utf8to16(it, eos, back_inserter(u16string));
+</pre>
+ <h3 id="fixinvalid">Ensure that a string contains valid UTF-8 text</h3>
+<p>
+If we have some text that "probably" contains UTF-8 encoded text and we want to
+replace any invalid UTF-8 sequence with a replacement character, something like
+the following function may be used:
+</p>
+<pre>
+<span class="keyword">void</span> fix_utf8_string(std::string& str)
+{
+ std::string temp;
+ utf8::replace_invalid(str.begin(), str.end(), back_inserter(temp));
+ str = temp;
+}
+</pre>
+<p>The function will replace any invalid UTF-8 sequence with a Unicode replacement character.
+There is an overloaded function that enables the caller to supply their own replacement character.
+</p>
+ <h2 id="reference">
+ Reference
+ </h2>
+ <h3 id="funutf8">
+ Functions From utf8 Namespace
+ </h3>
+ <h4>
+ utf8::append
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Encodes a 32 bit code point as a UTF-8 sequence of octets and appends the sequence
+ to a UTF-8 string.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+octet_iterator append(uint32_t cp, octet_iterator result);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an output iterator.<br>
+ <code>cp</code>: a 32 bit integer representing a code point to append to the
+ sequence.<br>
+ <code>result</code>: an output iterator to the place in the sequence where to
+ append the code point.<br>
+ <span class="return_value">Return value</span>: an iterator pointing to the place
+ after the newly appended sequence.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">unsigned char</span> u[<span class="literal">5</span>] = {<span
+class="literal">0</span>,<span class="literal">0</span>,<span class=
+"literal">0</span>,<span class="literal">0</span>,<span class="literal">0</span>};
+<span class="keyword">unsigned char</span>* end = append(<span class=
+"literal">0x0448</span>, u);
+assert (u[<span class="literal">0</span>] == <span class=
+"literal">0xd1</span> && u[<span class="literal">1</span>] == <span class=
+"literal">0x88</span> && u[<span class="literal">2</span>] == <span class=
+"literal">0</span> && u[<span class="literal">3</span>] == <span class=
+"literal">0</span> && u[<span class="literal">4</span>] == <span class=
+"literal">0</span>);
+</pre>
+ <p>
+ Note that <code>append</code> does not allocate any memory - it is the burden of
+ the caller to make sure there is enough memory allocated for the operation. To make
+ things more interesting, <code>append</code> can add anywhere between 1 and 4
+ octets to the sequence. In practice, you would most often want to use
+ <code>std::back_inserter</code> to ensure that the necessary memory is allocated.
+ </p>
+ <p>
+ In case of an invalid code point, a <code>utf8::invalid_code_point</code> exception
+ is thrown.
+ </p>
+ <h4>
+ utf8::next
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Given the iterator to the beginning of the UTF-8 sequence, it returns the code
+ point and moves the iterator to the next position.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t next(octet_iterator& it, octet_iterator end);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>it</code>: a reference to an iterator pointing to the beginning of an UTF-8
+ encoded code point. After the function returns, it is incremented to point to the
+ beginning of the next code point.<br>
+ <code>end</code>: end of the UTF-8 sequence to be processed. If <code>it</code>
+ gets equal to <code>end</code> during the extraction of a code point, an
+ <code>utf8::not_enough_room</code> exception is thrown.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ processed UTF-8 code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars;
+<span class="keyword">int</span> cp = next(w, twochars + <span class="literal">6</span>);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars + <span class="literal">3</span>);
+</pre>
+ <p>
+ This function is typically used to iterate through a UTF-8 encoded string.
+ </p>
+ <p>
+ In case of an invalid UTF-8 seqence, a <code>utf8::invalid_utf8</code> exception is
+ thrown.
+ </p>
+ <h4>
+ utf8::peek_next
+ </h4>
+ <p class="version">
+ Available in version 2.1 and later.
+ </p>
+ <p>
+ Given the iterator to the beginning of the UTF-8 sequence, it returns the code
+ point for the following sequence without changing the value of the iterator.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t peek_next(octet_iterator it, octet_iterator end);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>it</code>: an iterator pointing to the beginning of an UTF-8
+ encoded code point.<br>
+ <code>end</code>: end of the UTF-8 sequence to be processed. If <code>it</code>
+ gets equal to <code>end</code> during the extraction of a code point, an
+ <code>utf8::not_enough_room</code> exception is thrown.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ processed UTF-8 code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars;
+<span class="keyword">int</span> cp = peek_next(w, twochars + <span class="literal">6</span>);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars);
+</pre>
+ <p>
+ In case of an invalid UTF-8 seqence, a <code>utf8::invalid_utf8</code> exception is
+ thrown.
+ </p>
+ <h4>
+ utf8::prior
+ </h4>
+ <p class="version">
+ Available in version 1.02 and later.
+ </p>
+ <p>
+ Given a reference to an iterator pointing to an octet in a UTF-8 sequence, it
+ decreases the iterator until it hits the beginning of the previous UTF-8 encoded
+ code point and returns the 32 bits representation of the code point.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t prior(octet_iterator& it, octet_iterator start);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: a bidirectional iterator.<br>
+ <code>it</code>: a reference pointing to an octet within a UTF-8 encoded string.
+ After the function returns, it is decremented to point to the beginning of the
+ previous code point.<br>
+ <code>start</code>: an iterator to the beginning of the sequence where the search
+ for the beginning of a code point is performed. It is a
+ safety measure to prevent passing the beginning of the string in the search for a
+ UTF-8 lead octet.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ previous code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">unsigned char</span>* w = twochars + <span class=
+"literal">3</span>;
+<span class="keyword">int</span> cp = prior (w, twochars);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars);
+</pre>
+ <p>
+ This function has two purposes: one is two iterate backwards through a UTF-8
+ encoded string. Note that it is usually a better idea to iterate forward instead,
+ since <code>utf8::next</code> is faster. The second purpose is to find a beginning
+ of a UTF-8 sequence if we have a random position within a string. Note that in that
+ case <code>utf8::prior</code> may not detect an invalid UTF-8 sequence in some scenarios:
+ for instance if there are superfluous trail octets, it will just skip them.
+ </p>
+ <p>
+ <code>it</code> will typically point to the beginning of
+ a code point, and <code>start</code> will point to the
+ beginning of the string to ensure we don't go backwards too far. <code>it</code> is
+ decreased until it points to a lead UTF-8 octet, and then the UTF-8 sequence
+ beginning with that octet is decoded to a 32 bit representation and returned.
+ </p>
+ <p>
+ In case <code>start</code> is reached before a UTF-8 lead octet is hit, or if an
+ invalid UTF-8 sequence is started by the lead octet, an <code>invalid_utf8</code>
+ exception is thrown.
+ </p>
+ <p>In case <code>start</code> equals <code>it</code>, a <code>not_enough_room</code>
+ exception is thrown.
+ <h4>
+ utf8::previous
+ </h4>
+ <p class="version">
+ Deprecated in version 1.02 and later.
+ </p>
+ <p>
+ Given a reference to an iterator pointing to an octet in a UTF-8 seqence, it
+ decreases the iterator until it hits the beginning of the previous UTF-8 encoded
+ code point and returns the 32 bits representation of the code point.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t previous(octet_iterator& it, octet_iterator pass_start);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: a random access iterator.<br>
+ <code>it</code>: a reference pointing to an octet within a UTF-8 encoded string.
+ After the function returns, it is decremented to point to the beginning of the
+ previous code point.<br>
+ <code>pass_start</code>: an iterator to the point in the sequence where the search
+ for the beginning of a code point is aborted if no result was reached. It is a
+ safety measure to prevent passing the beginning of the string in the search for a
+ UTF-8 lead octet.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ previous code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">unsigned char</span>* w = twochars + <span class=
+"literal">3</span>;
+<span class="keyword">int</span> cp = previous (w, twochars - <span class=
+"literal">1</span>);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars);
+</pre>
+ <p>
+ <code>utf8::previous</code> is deprecated, and <code>utf8::prior</code> should
+ be used instead, although the existing code can continue using this function.
+ The problem is the parameter <code>pass_start</code> that points to the position
+ just before the beginning of the sequence. Standard containers don't have the
+ concept of "pass start" and the function can not be used with their iterators.
+ </p>
+ <p>
+ <code>it</code> will typically point to the beginning of
+ a code point, and <code>pass_start</code> will point to the octet just before the
+ beginning of the string to ensure we don't go backwards too far. <code>it</code> is
+ decreased until it points to a lead UTF-8 octet, and then the UTF-8 sequence
+ beginning with that octet is decoded to a 32 bit representation and returned.
+ </p>
+ <p>
+ In case <code>pass_start</code> is reached before a UTF-8 lead octet is hit, or if an
+ invalid UTF-8 sequence is started by the lead octet, an <code>invalid_utf8</code>
+ exception is thrown
+ </p>
+ <h4>
+ utf8::advance
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Advances an iterator by the specified number of code points within an UTF-8
+ sequence.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, typename distance_type>
+<span class=
+"keyword">void</span> advance (octet_iterator& it, distance_type n, octet_iterator end);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>distance_type</code>: an integral type convertible to <code>octet_iterator</code>'s difference type.<br>
+ <code>it</code>: a reference to an iterator pointing to the beginning of an UTF-8
+ encoded code point. After the function returns, it is incremented to point to the
+ nth following code point.<br>
+ <code>n</code>: a positive integer that shows how many code points we want to
+ advance.<br>
+ <code>end</code>: end of the UTF-8 sequence to be processed. If <code>it</code>
+ gets equal to <code>end</code> during the extraction of a code point, an
+ <code>utf8::not_enough_room</code> exception is thrown.<br>
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">unsigned char</span>* w = twochars;
+advance (w, <span class="literal">2</span>, twochars + <span class="literal">6</span>);
+assert (w == twochars + <span class="literal">5</span>);
+</pre>
+ <p>
+ This function works only "forward". In case of a negative <code>n</code>, there is
+ no effect.
+ </p>
+ <p>
+ In case of an invalid code point, a <code>utf8::invalid_code_point</code> exception
+ is thrown.
+ </p>
+ <h4>
+ utf8::distance
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Given the iterators to two UTF-8 encoded code points in a seqence, returns the
+ number of code points between them.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+<span class=
+"keyword">typename</span> std::iterator_traits<octet_iterator>::difference_type distance (octet_iterator first, octet_iterator last);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>first</code>: an iterator to a beginning of a UTF-8 encoded code point.<br>
+ <code>last</code>: an iterator to a "post-end" of the last UTF-8 encoded code
+ point in the sequence we are trying to determine the length. It can be the
+ beginning of a new code point, or not.<br>
+ <span class="return_value">Return value</span> the distance between the iterators,
+ in code points.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+size_t dist = utf8::distance(twochars, twochars + <span class="literal">5</span>);
+assert (dist == <span class="literal">2</span>);
+</pre>
+ <p>
+ This function is used to find the length (in code points) of a UTF-8 encoded
+ string. The reason it is called <em>distance</em>, rather than, say,
+ <em>length</em> is mainly because developers are used that <em>length</em> is an
+ O(1) function. Computing the length of an UTF-8 string is a linear operation, and
+ it looked better to model it after <code>std::distance</code> algorithm.
+ </p>
+ <p>
+ In case of an invalid UTF-8 seqence, a <code>utf8::invalid_utf8</code> exception is
+ thrown. If <code>last</code> does not point to the past-of-end of a UTF-8 seqence,
+ a <code>utf8::not_enough_room</code> exception is thrown.
+ </p>
+ <h4>
+ utf8::utf16to8
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts a UTF-16 encoded string to UTF-8.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> u16bit_iterator, <span class=
+"keyword">typename</span> octet_iterator>
+octet_iterator utf16to8 (u16bit_iterator start, u16bit_iterator end, octet_iterator result);
+
+</pre>
+ <p>
+ <code>u16bit_iterator</code>: an input iterator.<br>
+ <code>octet_iterator</code>: an output iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-16 encoded
+ string to convert.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-16 encoded
+ string to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-8 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-8 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">unsigned short</span> utf16string[] = {<span class=
+"literal">0x41</span>, <span class="literal">0x0448</span>, <span class=
+"literal">0x65e5</span>, <span class="literal">0xd834</span>, <span class=
+"literal">0xdd1e</span>};
+vector<<span class="keyword">unsigned char</span>> utf8result;
+utf16to8(utf16string, utf16string + <span class=
+"literal">5</span>, back_inserter(utf8result));
+assert (utf8result.size() == <span class="literal">10</span>);
+</pre>
+ <p>
+ In case of invalid UTF-16 sequence, a <code>utf8::invalid_utf16</code> exception is
+ thrown.
+ </p>
+ <h4>
+ utf8::utf8to16
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts an UTF-8 encoded string to UTF-16
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> u16bit_iterator, typename octet_iterator>
+u16bit_iterator utf8to16 (octet_iterator start, octet_iterator end, u16bit_iterator result);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>u16bit_iterator</code>: an output iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 encoded
+ string to convert. < br /> <code>end</code>: an iterator pointing to
+ pass-the-end of the UTF-8 encoded string to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-16 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-16 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span> utf8_with_surrogates[] = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88\xf0\x9d\x84\x9e"</span>;
+vector <<span class="keyword">unsigned short</span>> utf16result;
+utf8to16(utf8_with_surrogates, utf8_with_surrogates + <span class=
+"literal">9</span>, back_inserter(utf16result));
+assert (utf16result.size() == <span class="literal">4</span>);
+assert (utf16result[<span class="literal">2</span>] == <span class=
+"literal">0xd834</span>);
+assert (utf16result[<span class="literal">3</span>] == <span class=
+"literal">0xdd1e</span>);
+</pre>
+ <p>
+ In case of an invalid UTF-8 seqence, a <code>utf8::invalid_utf8</code> exception is
+ thrown. If <code>end</code> does not point to the past-of-end of a UTF-8 seqence, a
+ <code>utf8::not_enough_room</code> exception is thrown.
+ </p>
+ <h4>
+ utf8::utf32to8
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts a UTF-32 encoded string to UTF-8.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, typename u32bit_iterator>
+octet_iterator utf32to8 (u32bit_iterator start, u32bit_iterator end, octet_iterator result);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an output iterator.<br>
+ <code>u32bit_iterator</code>: an input iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-32 encoded
+ string to convert.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-32 encoded
+ string to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-8 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-8 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">int</span> utf32string[] = {<span class=
+"literal">0x448</span>, <span class="literal">0x65E5</span>, <span class=
+"literal">0x10346</span>, <span class="literal">0</span>};
+vector<<span class="keyword">unsigned char</span>> utf8result;
+utf32to8(utf32string, utf32string + <span class=
+"literal">3</span>, back_inserter(utf8result));
+assert (utf8result.size() == <span class="literal">9</span>);
+</pre>
+ <p>
+ In case of invalid UTF-32 string, a <code>utf8::invalid_code_point</code> exception
+ is thrown.
+ </p>
+ <h4>
+ utf8::utf8to32
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts a UTF-8 encoded string to UTF-32.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, <span class=
+"keyword">typename</span> u32bit_iterator>
+u32bit_iterator utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>u32bit_iterator</code>: an output iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 encoded
+ string to convert.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-8 encoded string
+ to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-32 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-32 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+vector<<span class="keyword">int</span>> utf32result;
+utf8to32(twochars, twochars + <span class=
+"literal">5</span>, back_inserter(utf32result));
+assert (utf32result.size() == <span class="literal">2</span>);
+</pre>
+ <p>
+ In case of an invalid UTF-8 seqence, a <code>utf8::invalid_utf8</code> exception is
+ thrown. If <code>end</code> does not point to the past-of-end of a UTF-8 seqence, a
+ <code>utf8::not_enough_room</code> exception is thrown.
+ </p>
+ <h4>
+ utf8::find_invalid
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Detects an invalid sequence within a UTF-8 string.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+octet_iterator find_invalid(octet_iterator start, octet_iterator end);
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 string to
+ test for validity.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-8 string to test
+ for validity.<br>
+ <span class="return_value">Return value</span>: an iterator pointing to the first
+ invalid octet in the UTF-8 string. In case none were found, equals
+ <code>end</code>.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span> utf_invalid[] = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88\xfa"</span>;
+<span class=
+"keyword">char</span>* invalid = find_invalid(utf_invalid, utf_invalid + <span class=
+"literal">6</span>);
+assert (invalid == utf_invalid + <span class="literal">5</span>);
+</pre>
+ <p>
+ This function is typically used to make sure a UTF-8 string is valid before
+ processing it with other functions. It is especially important to call it if before
+ doing any of the <em>unchecked</em> operations on it.
+ </p>
+ <h4>
+ utf8::is_valid
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Checks whether a sequence of octets is a valid UTF-8 string.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+<span class="keyword">bool</span> is_valid(octet_iterator start, octet_iterator end);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 string to
+ test for validity.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-8 string to test
+ for validity.<br>
+ <span class="return_value">Return value</span>: <code>true</code> if the sequence
+ is a valid UTF-8 string; <code>false</code> if not.
+ </p>
+ Example of use:
+<pre>
+<span class="keyword">char</span> utf_invalid[] = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88\xfa"</span>;
+<span class="keyword">bool</span> bvalid = is_valid(utf_invalid, utf_invalid + <span
+class="literal">6</span>);
+assert (bvalid == false);
+</pre>
+ <p>
+ <code>is_valid</code> is a shorthand for <code>find_invalid(start, end) ==
+ end;</code>. You may want to use it to make sure that a byte seqence is a valid
+ UTF-8 string without the need to know where it fails if it is not valid.
+ </p>
+ <h4>
+ utf8::replace_invalid
+ </h4>
+ <p class="version">
+ Available in version 2.0 and later.
+ </p>
+ <p>
+ Replaces all invalid UTF-8 sequences within a string with a replacement marker.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, <span class=
+"keyword">typename</span> output_iterator>
+output_iterator replace_invalid(octet_iterator start, octet_iterator end, output_iterator out, uint32_t replacement);
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, <span class=
+"keyword">typename</span> output_iterator>
+output_iterator replace_invalid(octet_iterator start, octet_iterator end, output_iterator out);
+
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>output_iterator</code>: an output iterator.<br>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 string to
+ look for invalid UTF-8 sequences.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-8 string to look
+ for invalid UTF-8 sequences.<br>
+ <code>out</code>: An output iterator to the range where the result of replacement
+ is stored.<br>
+ <code>replacement</code>: A Unicode code point for the replacement marker. The
+ version without this parameter assumes the value <code>0xfffd</code><br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the UTF-8 string with replaced invalid sequences.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span> invalid_sequence[] = <span class=
+"literal">"a\x80\xe0\xa0\xc0\xaf\xed\xa0\x80z"</span>;
+vector<<span class="keyword">char</span>> replace_invalid_result;
+replace_invalid (invalid_sequence, invalid_sequence + sizeof(invalid_sequence), back_inserter(replace_invalid_result), <span
+ class="literal">'?'</span>);
+bvalid = is_valid(replace_invalid_result.begin(), replace_invalid_result.end());
+assert (bvalid);
+<span class="keyword">char</span>* fixed_invalid_sequence = <span class=
+"literal">"a????z"</span>;
+assert (std::equal(replace_invalid_result.begin(), replace_invalid_result.end(), fixed_invalid_sequence));
+</pre>
+ <p>
+ <code>replace_invalid</code> does not perform in-place replacement of invalid
+ sequences. Rather, it produces a copy of the original string with the invalid
+ sequences replaced with a replacement marker. Therefore, <code>out</code> must not
+ be in the <code>[start, end]</code> range.
+ </p>
+ <p>
+ If <code>end</code> does not point to the past-of-end of a UTF-8 sequence, a
+ <code>utf8::not_enough_room</code> exception is thrown.
+ </p>
+ <h4>
+ utf8::starts_with_bom
+ </h4>
+ <p class="version">
+ Available in version 2.3 and later. Relaces deprecated <code>is_bom()</code> function.
+ </p>
+ <p>
+ Checks whether an octet sequence starts with a UTF-8 byte order mark (BOM)
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+<span class="keyword">bool</span> starts_with_bom (octet_iterator it, octet_iterator end);
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>it</code>: beginning of the octet sequence to check<br>
+ <code>end</code>: pass-end of the sequence to check<br>
+ <span class="return_value">Return value</span>: <code>true</code> if the sequence
+ starts with a UTF-8 byte order mark; <code>false</code> if not.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">unsigned char</span> byte_order_mark[] = {<span class=
+"literal">0xef</span>, <span class="literal">0xbb</span>, <span class=
+"literal">0xbf</span>};
+<span class="keyword">bool</span> bbom = starts_with_bom(byte_order_mark, byte_order_mark + <span class="keyword">sizeof</span>(byte_order_mark));
+assert (bbom == <span class="literal">true</span>);
+</pre>
+ <p>
+ The typical use of this function is to check the first three bytes of a file. If
+ they form the UTF-8 BOM, we want to skip them before processing the actual UTF-8
+ encoded text.
+ </p>
+ <h4>
+ utf8::is_bom
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later. Deprecated in version 2.3. <code>starts_with_bom()</code> should be used
+ instead.
+ </p>
+ <p>
+ Checks whether a sequence of three octets is a UTF-8 byte order mark (BOM)
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+<span class="keyword">bool</span> is_bom (octet_iterator it); <span class="comment"> // Deprecated</span>
+</pre>
+ <p>
+ <code>octet_iterator</code>: an input iterator.<br>
+ <code>it</code>: beginning of the 3-octet sequence to check<br>
+ <span class="return_value">Return value</span>: <code>true</code> if the sequence
+ is UTF-8 byte order mark; <code>false</code> if not.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">unsigned char</span> byte_order_mark[] = {<span class=
+"literal">0xef</span>, <span class="literal">0xbb</span>, <span class=
+"literal">0xbf</span>};
+<span class="keyword">bool</span> bbom = is_bom(byte_order_mark);
+assert (bbom == <span class="literal">true</span>);
+</pre>
+ <p>
+ The typical use of this function is to check the first three bytes of a file. If
+ they form the UTF-8 BOM, we want to skip them before processing the actual UTF-8
+ encoded text.
+ </p>
+ <p>
+ If a sequence is
+ shorter than three bytes, an invalid iterator will be dereferenced. Therefore, this function is deprecated
+ in favor of <code>starts_with_bom()</code>that takes the end of sequence as an argument.
+ </p>
+ <h3 id="typesutf8">
+ Types From utf8 Namespace
+ </h3>
+ <h4>utf8::exception
+ </h4>
+ <p class="version">
+ Available in version 2.3 and later.
+ </p>
+ <p>
+ Base class for the exceptions thrown by UTF CPP library functions.
+ </p>
+<pre>
+<span class="keyword">class</span> exception : <span class="keyword">public</span> std::exception {};
+</pre>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">try</span> {
+ code_that_uses_utf_cpp_library();
+}
+<span class="keyword">catch</span>(<span class="keyword">const</span> utf8::exception& utfcpp_ex) {
+ cerr << utfcpp_ex.what();
+}
+</pre>
+
+ <h4>utf8::invalid_code_point
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Thrown by UTF8 CPP functions such as <code>advance</code> and <code>next</code> if an UTF-8 sequence represents and invalid code point.
+ </p>
+
+<pre>
+<span class="keyword">class</span> invalid_code_point : <span class="keyword">public</span> exception {
+<span class="keyword">public</span>:
+ uint32_t code_point() <span class="keyword">const</span>;
+};
+
+</pre>
+ <p>
+ Member function <code>code_point()</code> can be used to determine the invalid code point that
+ caused the exception to be thrown.
+ </p>
+ <h4>utf8::invalid_utf8
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Thrown by UTF8 CPP functions such as <code>next</code> and <code>prior</code> if an invalid UTF-8 sequence
+ is detected during decoding.
+ </p>
+
+<pre>
+<span class="keyword">class</span> invalid_utf8 : <span class="keyword">public</span> exception {
+<span class="keyword">public</span>:
+ uint8_t utf8_octet() <span class="keyword">const</span>;
+};
+</pre>
+
+ <p>
+ Member function <code>utf8_octet()</code> can be used to determine the beginning of the byte
+ sequence that caused the exception to be thrown.
+ </p>
+</pre>
+ <h4>utf8::invalid_utf16
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Thrown by UTF8 CPP function <code>utf16to8</code> if an invalid UTF-16 sequence
+ is detected during decoding.
+ </p>
+
+<pre>
+<span class="keyword">class</span> invalid_utf16 : <span class="keyword">public</span> exception {
+<span class="keyword">public</span>:
+ uint16_t utf16_word() <span class="keyword">const</span>;
+};
+</pre>
+
+ <p>
+ Member function <code>utf16_word()</code> can be used to determine the UTF-16 code unit
+ that caused the exception to be thrown.
+ </p>
+ <h4>utf8::not_enough_room
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Thrown by UTF8 CPP functions such as <code>next</code> if the end of the decoded UTF-8 sequence
+ was reached before the code point was decoded.
+ </p>
+
+<pre>
+<span class="keyword">class</span> not_enough_room : <span class="keyword">public</span> exception {};
+</pre>
+ <h4>
+ utf8::iterator
+ </h4>
+ <p class="version">
+ Available in version 2.0 and later.
+ </p>
+ <p>
+ Adapts the underlying octet iterator to iterate over the sequence of code points,
+ rather than raw octets.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class="keyword">typename</span> octet_iterator>
+<span class="keyword">class</span> iterator;
+</pre>
+
+ <h5>Member functions</h5>
+ <dl>
+ <dt><code>iterator();</code> <dd> the deafult constructor; the underlying <code>octet_iterator</code> is
+ constructed with its default constructor.
+ <dt><code><span class="keyword">explicit</span> iterator (const octet_iterator& octet_it,
+ const octet_iterator& range_start,
+ const octet_iterator& range_end);</code> <dd> a constructor
+ that initializes the underlying <code>octet_iterator</code> with <code>octet_it</code>
+ and sets the range in which the iterator is considered valid.
+ <dt><code>octet_iterator base () <span class="keyword">const</span>;</code> <dd> returns the
+ underlying <code>octet_iterator</code>.
+ <dt><code>uint32_t operator * () <span class="keyword">const</span>;</code> <dd> decodes the utf-8 sequence
+ the underlying <code>octet_iterator</code> is pointing to and returns the code point.
+ <dt><code><span class="keyword">bool operator</span> == (const iterator& rhs)
+ <span class="keyword">const</span>;</code> <dd> returns <span class="keyword">true</span>
+ if the two underlaying iterators are equal.
+ <dt><code><span class="keyword">bool operator</span> != (const iterator& rhs)
+ <span class="keyword">const</span>;</code> <dd> returns <span class="keyword">true</span>
+ if the two underlaying iterators are not equal.
+ <dt><code>iterator& <span class="keyword">operator</span> ++ (); </code> <dd> the prefix increment - moves
+ the iterator to the next UTF-8 encoded code point.
+ <dt><code>iterator <span class="keyword">operator</span> ++ (<span class="keyword">int</span>); </code> <dd>
+ the postfix increment - moves the iterator to the next UTF-8 encoded code point and returns the current one.
+ <dt><code>iterator& <span class="keyword">operator</span> -- (); </code> <dd> the prefix decrement - moves
+ the iterator to the previous UTF-8 encoded code point.
+ <dt><code>iterator <span class="keyword">operator</span> -- (<span class="keyword">int</span>); </code> <dd>
+ the postfix decrement - moves the iterator to the previous UTF-8 encoded code point and returns the current one.
+ </dl>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* threechars = <span class="literal">"\xf0\x90\x8d\x86\xe6\x97\xa5\xd1\x88"</span>;
+utf8::iterator<<span class="keyword">char</span>*> it(threechars, threechars, threechars + <span class="literal">9</span>);
+utf8::iterator<<span class="keyword">char</span>*> it2 = it;
+assert (it2 == it);
+assert (*it == <span class="literal">0x10346</span>);
+assert (*(++it) == <span class="literal">0x65e5</span>);
+assert ((*it++) == <span class="literal">0x65e5</span>);
+assert (*it == <span class="literal">0x0448</span>);
+assert (it != it2);
+utf8::iterator<<span class="keyword">char</span>*> endit (threechars + <span class="literal">9</span>, threechars, threechars + <span class="literal">9</span>);
+assert (++it == endit);
+assert (*(--it) == <span class="literal">0x0448</span>);
+assert ((*it--) == <span class="literal">0x0448</span>);
+assert (*it == <span class="literal">0x65e5</span>);
+assert (--it == utf8::iterator<<span class="keyword">char</span>*>(threechars, threechars, threechars + <span class="literal">9</span>));
+assert (*it == <span class="literal">0x10346</span>);
+</pre>
+ <p>
+ The purpose of <code>utf8::iterator</code> adapter is to enable easy iteration as well as the use of STL
+ algorithms with UTF-8 encoded strings. Increment and decrement operators are implemented in terms of
+ <code>utf8::next()</code> and <code>utf8::prior()</code> functions.
+ </p>
+ <p>
+ Note that <code>utf8::iterator</code> adapter is a checked iterator. It operates on the range specified in
+ the constructor; any attempt to go out of that range will result in an exception. Even the comparison operators
+ require both iterator object to be constructed against the same range - otherwise an exception is thrown. Typically,
+ the range will be determined by sequence container functions <code>begin</code> and <code>end</code>, i.e.:
+ </p>
+<pre>
+std::string s = <span class="literal">"example"</span>;
+utf8::iterator i (s.begin(), s.begin(), s.end());
+</pre>
+ <h3 id="fununchecked">
+ Functions From utf8::unchecked Namespace
+ </h3>
+ <h4>
+ utf8::unchecked::append
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Encodes a 32 bit code point as a UTF-8 sequence of octets and appends the sequence
+ to a UTF-8 string.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+octet_iterator append(uint32_t cp, octet_iterator result);
+
+</pre>
+ <p>
+ <code>cp</code>: A 32 bit integer representing a code point to append to the
+ sequence.<br>
+ <code>result</code>: An output iterator to the place in the sequence where to
+ append the code point.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the newly appended sequence.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">unsigned char</span> u[<span class="literal">5</span>] = {<span
+class="literal">0</span>,<span class="literal">0</span>,<span class=
+"literal">0</span>,<span class="literal">0</span>,<span class="literal">0</span>};
+<span class="keyword">unsigned char</span>* end = unchecked::append(<span class=
+"literal">0x0448</span>, u);
+assert (u[<span class="literal">0</span>] == <span class=
+"literal">0xd1</span> && u[<span class="literal">1</span>] == <span class=
+"literal">0x88</span> && u[<span class="literal">2</span>] == <span class=
+"literal">0</span> && u[<span class="literal">3</span>] == <span class=
+"literal">0</span> && u[<span class="literal">4</span>] == <span class=
+"literal">0</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::append</code>. It does not
+ check for validity of the supplied code point, and may produce an invalid UTF-8
+ sequence.
+ </p>
+ <h4>
+ utf8::unchecked::next
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Given the iterator to the beginning of a UTF-8 sequence, it returns the code point
+ and moves the iterator to the next position.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t next(octet_iterator& it);
+
+</pre>
+ <p>
+ <code>it</code>: a reference to an iterator pointing to the beginning of an UTF-8
+ encoded code point. After the function returns, it is incremented to point to the
+ beginning of the next code point.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ processed UTF-8 code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars;
+<span class="keyword">int</span> cp = unchecked::next(w);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars + <span class="literal">3</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::next</code>. It does not
+ check for validity of the supplied UTF-8 sequence.
+ </p>
+ <h4>
+ utf8::unchecked::peek_next
+ </h4>
+ <p class="version">
+ Available in version 2.1 and later.
+ </p>
+ <p>
+ Given the iterator to the beginning of a UTF-8 sequence, it returns the code point.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t peek_next(octet_iterator it);
+
+</pre>
+ <p>
+ <code>it</code>: an iterator pointing to the beginning of an UTF-8
+ encoded code point.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ processed UTF-8 code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars;
+<span class="keyword">int</span> cp = unchecked::peek_next(w);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::peek_next</code>. It does not
+ check for validity of the supplied UTF-8 sequence.
+ </p>
+ <h4>
+ utf8::unchecked::prior
+ </h4>
+ <p class="version">
+ Available in version 1.02 and later.
+ </p>
+ <p>
+ Given a reference to an iterator pointing to an octet in a UTF-8 seqence, it
+ decreases the iterator until it hits the beginning of the previous UTF-8 encoded
+ code point and returns the 32 bits representation of the code point.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t prior(octet_iterator& it);
+
+</pre>
+ <p>
+ <code>it</code>: a reference pointing to an octet within a UTF-8 encoded string.
+ After the function returns, it is decremented to point to the beginning of the
+ previous code point.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ previous code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars + <span class="literal">3</span>;
+<span class="keyword">int</span> cp = unchecked::prior (w);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::prior</code>. It does not
+ check for validity of the supplied UTF-8 sequence and offers no boundary checking.
+ </p>
+ <h4>
+ utf8::unchecked::previous (deprecated, see utf8::unchecked::prior)
+ </h4>
+ <p class="version">
+ Deprecated in version 1.02 and later.
+ </p>
+ <p>
+ Given a reference to an iterator pointing to an octet in a UTF-8 seqence, it
+ decreases the iterator until it hits the beginning of the previous UTF-8 encoded
+ code point and returns the 32 bits representation of the code point.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+uint32_t previous(octet_iterator& it);
+
+</pre>
+ <p>
+ <code>it</code>: a reference pointing to an octet within a UTF-8 encoded string.
+ After the function returns, it is decremented to point to the beginning of the
+ previous code point.<br>
+ <span class="return_value">Return value</span>: the 32 bit representation of the
+ previous code point.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars + <span class="literal">3</span>;
+<span class="keyword">int</span> cp = unchecked::previous (w);
+assert (cp == <span class="literal">0x65e5</span>);
+assert (w == twochars);
+</pre>
+ <p>
+ The reason this function is deprecated is just the consistency with the "checked"
+ versions, where <code>prior</code> should be used instead of <code>previous</code>.
+ In fact, <code>unchecked::previous</code> behaves exactly the same as <code>
+ unchecked::prior</code>
+ </p>
+ <p>
+ This is a faster but less safe version of <code>utf8::previous</code>. It does not
+ check for validity of the supplied UTF-8 sequence and offers no boundary checking.
+ </p>
+ <h4>
+ utf8::unchecked::advance
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Advances an iterator by the specified number of code points within an UTF-8
+ sequence.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, typename distance_type>
+<span class="keyword">void</span> advance (octet_iterator& it, distance_type n);
+
+</pre>
+ <p>
+ <code>it</code>: a reference to an iterator pointing to the beginning of an UTF-8
+ encoded code point. After the function returns, it is incremented to point to the
+ nth following code point.<br>
+ <code>n</code>: a positive integer that shows how many code points we want to
+ advance.<br>
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+<span class="keyword">char</span>* w = twochars;
+unchecked::advance (w, <span class="literal">2</span>);
+assert (w == twochars + <span class="literal">5</span>);
+</pre>
+ <p>
+ This function works only "forward". In case of a negative <code>n</code>, there is
+ no effect.
+ </p>
+ <p>
+ This is a faster but less safe version of <code>utf8::advance</code>. It does not
+ check for validity of the supplied UTF-8 sequence and offers no boundary checking.
+ </p>
+ <h4>
+ utf8::unchecked::distance
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Given the iterators to two UTF-8 encoded code points in a seqence, returns the
+ number of code points between them.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator>
+<span class=
+"keyword">typename</span> std::iterator_traits<octet_iterator>::difference_type distance (octet_iterator first, octet_iterator last);
+</pre>
+ <p>
+ <code>first</code>: an iterator to a beginning of a UTF-8 encoded code point.<br>
+ <code>last</code>: an iterator to a "post-end" of the last UTF-8 encoded code
+ point in the sequence we are trying to determine the length. It can be the
+ beginning of a new code point, or not.<br>
+ <span class="return_value">Return value</span> the distance between the iterators,
+ in code points.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+size_t dist = utf8::unchecked::distance(twochars, twochars + <span class=
+"literal">5</span>);
+assert (dist == <span class="literal">2</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::distance</code>. It does not
+ check for validity of the supplied UTF-8 sequence.
+ </p>
+ <h4>
+ utf8::unchecked::utf16to8
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts a UTF-16 encoded string to UTF-8.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> u16bit_iterator, <span class=
+"keyword">typename</span> octet_iterator>
+octet_iterator utf16to8 (u16bit_iterator start, u16bit_iterator end, octet_iterator result);
+
+</pre>
+ <p>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-16 encoded
+ string to convert.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-16 encoded
+ string to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-8 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-8 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">unsigned short</span> utf16string[] = {<span class=
+"literal">0x41</span>, <span class="literal">0x0448</span>, <span class=
+"literal">0x65e5</span>, <span class="literal">0xd834</span>, <span class=
+"literal">0xdd1e</span>};
+vector<<span class="keyword">unsigned char</span>> utf8result;
+unchecked::utf16to8(utf16string, utf16string + <span class=
+"literal">5</span>, back_inserter(utf8result));
+assert (utf8result.size() == <span class="literal">10</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::utf16to8</code>. It does not
+ check for validity of the supplied UTF-16 sequence.
+ </p>
+ <h4>
+ utf8::unchecked::utf8to16
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts an UTF-8 encoded string to UTF-16
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> u16bit_iterator, typename octet_iterator>
+u16bit_iterator utf8to16 (octet_iterator start, octet_iterator end, u16bit_iterator result);
+
+</pre>
+ <p>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 encoded
+ string to convert. < br /> <code>end</code>: an iterator pointing to
+ pass-the-end of the UTF-8 encoded string to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-16 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-16 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span> utf8_with_surrogates[] = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88\xf0\x9d\x84\x9e"</span>;
+vector <<span class="keyword">unsigned short</span>> utf16result;
+unchecked::utf8to16(utf8_with_surrogates, utf8_with_surrogates + <span class=
+"literal">9</span>, back_inserter(utf16result));
+assert (utf16result.size() == <span class="literal">4</span>);
+assert (utf16result[<span class="literal">2</span>] == <span class=
+"literal">0xd834</span>);
+assert (utf16result[<span class="literal">3</span>] == <span class=
+"literal">0xdd1e</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::utf8to16</code>. It does not
+ check for validity of the supplied UTF-8 sequence.
+ </p>
+ <h4>
+ utf8::unchecked::utf32to8
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts a UTF-32 encoded string to UTF-8.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, <span class=
+"keyword">typename</span> u32bit_iterator>
+octet_iterator utf32to8 (u32bit_iterator start, u32bit_iterator end, octet_iterator result);
+
+</pre>
+ <p>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-32 encoded
+ string to convert.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-32 encoded
+ string to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-8 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-8 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">int</span> utf32string[] = {<span class=
+"literal">0x448</span>, <span class="literal">0x65e5</span>, <span class=
+"literal">0x10346</span>, <span class="literal">0</span>};
+vector<<span class="keyword">unsigned char</span>> utf8result;
+utf32to8(utf32string, utf32string + <span class=
+"literal">3</span>, back_inserter(utf8result));
+assert (utf8result.size() == <span class="literal">9</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::utf32to8</code>. It does not
+ check for validity of the supplied UTF-32 sequence.
+ </p>
+ <h4>
+ utf8::unchecked::utf8to32
+ </h4>
+ <p class="version">
+ Available in version 1.0 and later.
+ </p>
+ <p>
+ Converts a UTF-8 encoded string to UTF-32.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class=
+"keyword">typename</span> octet_iterator, typename u32bit_iterator>
+u32bit_iterator utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result);
+
+</pre>
+ <p>
+ <code>start</code>: an iterator pointing to the beginning of the UTF-8 encoded
+ string to convert.<br>
+ <code>end</code>: an iterator pointing to pass-the-end of the UTF-8 encoded string
+ to convert.<br>
+ <code>result</code>: an output iterator to the place in the UTF-32 string where to
+ append the result of conversion.<br>
+ <span class="return_value">Return value</span>: An iterator pointing to the place
+ after the appended UTF-32 string.
+ </p>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* twochars = <span class=
+"literal">"\xe6\x97\xa5\xd1\x88"</span>;
+vector<<span class="keyword">int</span>> utf32result;
+unchecked::utf8to32(twochars, twochars + <span class=
+"literal">5</span>, back_inserter(utf32result));
+assert (utf32result.size() == <span class="literal">2</span>);
+</pre>
+ <p>
+ This is a faster but less safe version of <code>utf8::utf8to32</code>. It does not
+ check for validity of the supplied UTF-8 sequence.
+ </p>
+ <h3 id="typesunchecked">
+ Types From utf8::unchecked Namespace
+ </h3>
+ <h4>
+ utf8::iterator
+ </h4>
+ <p class="version">
+ Available in version 2.0 and later.
+ </p>
+ <p>
+ Adapts the underlying octet iterator to iterate over the sequence of code points,
+ rather than raw octets.
+ </p>
+<pre>
+<span class="keyword">template</span> <<span class="keyword">typename</span> octet_iterator>
+<span class="keyword">class</span> iterator;
+</pre>
+
+ <h5>Member functions</h5>
+ <dl>
+ <dt><code>iterator();</code> <dd> the deafult constructor; the underlying <code>octet_iterator</code> is
+ constructed with its default constructor.
+ <dt><code><span class="keyword">explicit</span> iterator (const octet_iterator& octet_it);
+ </code> <dd> a constructor
+ that initializes the underlying <code>octet_iterator</code> with <code>octet_it</code>
+ <dt><code>octet_iterator base () <span class="keyword">const</span>;</code> <dd> returns the
+ underlying <code>octet_iterator</code>.
+ <dt><code>uint32_t operator * () <span class="keyword">const</span>;</code> <dd> decodes the utf-8 sequence
+ the underlying <code>octet_iterator</code> is pointing to and returns the code point.
+ <dt><code><span class="keyword">bool operator</span> == (const iterator& rhs)
+ <span class="keyword">const</span>;</code> <dd> returns <span class="keyword">true</span>
+ if the two underlaying iterators are equal.
+ <dt><code><span class="keyword">bool operator</span> != (const iterator& rhs)
+ <span class="keyword">const</span>;</code> <dd> returns <span class="keyword">true</span>
+ if the two underlaying iterators are not equal.
+ <dt><code>iterator& <span class="keyword">operator</span> ++ (); </code> <dd> the prefix increment - moves
+ the iterator to the next UTF-8 encoded code point.
+ <dt><code>iterator <span class="keyword">operator</span> ++ (<span class="keyword">int</span>); </code> <dd>
+ the postfix increment - moves the iterator to the next UTF-8 encoded code point and returns the current one.
+ <dt><code>iterator& <span class="keyword">operator</span> -- (); </code> <dd> the prefix decrement - moves
+ the iterator to the previous UTF-8 encoded code point.
+ <dt><code>iterator <span class="keyword">operator</span> -- (<span class="keyword">int</span>); </code> <dd>
+ the postfix decrement - moves the iterator to the previous UTF-8 encoded code point and returns the current one.
+ </dl>
+ <p>
+ Example of use:
+ </p>
+<pre>
+<span class="keyword">char</span>* threechars = <span class="literal">"\xf0\x90\x8d\x86\xe6\x97\xa5\xd1\x88"</span>;
+utf8::unchecked::iterator<<span class="keyword">char</span>*> un_it(threechars);
+utf8::unchecked::iterator<<span class="keyword">char</span>*> un_it2 = un_it;
+assert (un_it2 == un_it);
+assert (*un_it == <span class="literal">0x10346</span>);
+assert (*(++un_it) == <span class="literal">0x65e5</span>);
+assert ((*un_it++) == <span class="literal">0x65e5</span>);
+assert (*un_it == <span class="literal">0x0448</span>);
+assert (un_it != un_it2);
+utf8::::unchecked::iterator<<span class="keyword">char</span>*> un_endit (threechars + <span class="literal">9</span>);
+assert (++un_it == un_endit);
+assert (*(--un_it) == <span class="literal">0x0448</span>);
+assert ((*un_it--) == <span class="literal">0x0448</span>);
+assert (*un_it == <span class="literal">0x65e5</span>);
+assert (--un_it == utf8::unchecked::iterator<<span class="keyword">char</span>*>(threechars));
+assert (*un_it == <span class="literal">0x10346</span>);
+</pre>
+ <p>
+ This is an unchecked version of <code>utf8::iterator</code>. It is faster in many cases, but offers
+ no validity or range checks.
+ </p>
+ <h2 id="points">
+ Points of interest
+ </h2>
+ <h4>
+ Design goals and decisions
+ </h4>
+ <p>
+ The library was designed to be:
+ </p>
+ <ol>
+ <li>
+ Generic: for better or worse, there are many C++ string classes out there, and
+ the library should work with as many of them as possible.
+ </li>
+ <li>
+ Portable: the library should be portable both accross different platforms and
+ compilers. The only non-portable code is a small section that declares unsigned
+ integers of different sizes: three typedefs. They can be changed by the users of
+ the library if they don't match their platform. The default setting should work
+ for Windows (both 32 and 64 bit), and most 32 bit and 64 bit Unix derivatives.
+ </li>
+ <li>
+ Lightweight: follow the "pay only for what you use" guideline.
+ </li>
+ <li>
+ Unintrusive: avoid forcing any particular design or even programming style on the
+ user. This is a library, not a framework.
+ </li>
+ </ol>
+ <h4>
+ Alternatives
+ </h4>
+ <p>
+ In case you want to look into other means of working with UTF-8 strings from C++,
+ here is the list of solutions I am aware of:
+ </p>
+ <ol>
+ <li>
+ <a href="http://icu.sourceforge.net/">ICU Library</a>. It is very powerful,
+ complete, feature-rich, mature, and widely used. Also big, intrusive,
+ non-generic, and doesn't play well with the Standard Library. I definitelly
+ recommend looking at ICU even if you don't plan to use it.
+ </li>
+ <li>
+ C++11 language and library features. Still far from complete, and not widely
+ supported by compiler vendors.
+ </li>
+ <li>
+ <a href=
+ "http://www.gtkmm.org/gtkmm2/docs/tutorial/html/ch03s04.html">Glib::ustring</a>.
+ A class specifically made to work with UTF-8 strings, and also feel like
+ <code>std::string</code>. If you prefer to have yet another string class in your
+ code, it may be worth a look. Be aware of the licensing issues, though.
+ </li>
+ <li>
+ Platform dependent solutions: Windows and POSIX have functions to convert strings
+ from one encoding to another. That is only a subset of what my library offers,
+ but if that is all you need it may be good enough.
+ </li>
+ </ol>
+ <h2 id="links">
+ Links
+ </h2>
+ <ol>
+ <li>
+ <a href="http://www.unicode.org/">The Unicode Consortium</a>.
+ </li>
+ <li>
+ <a href="http://icu.sourceforge.net/">ICU Library</a>.
+ </li>
+ <li>
+ <a href="http://en.wikipedia.org/wiki/UTF-8">UTF-8 at Wikipedia</a>
+ </li>
+ <li>
+ <a href="http://www.cl.cam.ac.uk/~mgk25/unicode.html">UTF-8 and Unicode FAQ for
+ Unix/Linux</a>
+ </li>
+ </ol>
+ </body>
+</html>
projects / simgear.git / commitdiff