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<head>
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<body>
<h2>Introduction</h2>
<p>Many C++ developers miss an easy and portable way of handling
Unicode encoded strings. C++ Standard is currently Unicode
agnostic, and while some work is being done to introduce Unicode to
the next incarnation called C++0x, for the moment nothing of the
sort is available. In the meantime, developers use 3rd 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 have
come up with a set of template functions. For anybody used to work
with STL algorithms, they 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. Be aware, though, that while I
did some testing, this library has not been used in production yet.
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>Examples of use</h2>
<p>To illustrate the use of this utf8 library, we shall open a file
containing a line of UTF-8 encoded text, read the line into
<code>std::string</code>, convert the text to UTF-16, and write it
to another file:</p>
<pre>
#include &lt;fstream&gt;
#include &lt;iostream&gt;
#include &lt;string&gt;
#include &lt;vector&gt;
using namespace std;
int main()
{
// Open the file with a utf-8 encoded line of text in it
ifstream fs8("utf8.txt");
if (!fs8.is_open()) {
cout &lt;&lt; "Could not open utf8.txt" &lt;&lt; endl;
return 0;
}
// is there a utf8 marker? if yes, skip it.
fs8.seekg(0, ios::end);
ifstream::pos_type file_length = fs8.tellg();
fs8.seekg(0, ios::beg);
if (file_length &gt; 3) {
char bom[3];
fs8.read(bom, 3);
if (!utf8::is_bom(bom))
fs8.seekg(0, ios::beg);
}
// Read the line from the file
string text8;
getline(fs8, text8);
// Make sure it is valid utf-8
if (!utf8::is_valid(text8.begin(), text8.end())) {
cout &lt;&lt; "Invalid utf-8 text";
return 0;
}
// Convert the text to utf-16
vector&lt;unsigned short&gt; text16;
text16.push_back(0xfeff); // bom
utf8::utf8to16(text8.begin(), text8.end(), back_inserter(text16));
// Create the file for writing the utf-16 string
ofstream fs16("utf16.txt", ios_base::out | ios_base::binary);
if (!fs16.is_open()) {
cout &lt;&lt; "Could not open utf16.txt" &lt;&lt; endl;
return 0;
}
// Write the utf16 text to the file
fs16.write(reinterpret_cast&lt;const char*&gt;(&amp;text16[0]), text16.size() * sizeof (unsigned short));
}
</pre>
<p>In the previous code sample, we have seen the use of 3 functions
from <code>utf8</code> namespace: first we used <code>is_bom</code>
function to detect UTF-8 byte order mark at the beginning of the
file, then <code>is_valid</code> to make sure that the text we
loaded is valid UTF-8, and finally <code>utf8to16</code> to convert
the text to UTF-16 encoding. Note that the use of
<code>is_valid</code> was optional in this case;
<code>utf8to16</code> throws an exception in case of invalid UTF-8
text.</p>
<h2>Reference</h2>
<h3>Functions From utf8 Namespace</h3>
<h4>utf8::append</h4>
<p>Encodes a 32 bit code point as a UTF-8 sequence of octets and
appends the sequence to a UTF-8 string.</p>
<code>template &lt;typename octet_iterator&gt; octet_iterator
append(uint32_t cp, octet_iterator result);</code>
<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>
<u>Return value</u>: An iterator pointing to the place after the
newly appended sequence.</p>
<p>Example of use:</p>
<pre>
unsigned char u[5] = {0,0,0,0,0};
unsigned char* end = append(0x0448, u);
assert (u[0] == 0xd1 &amp;&amp; u[1] == 0x88 &amp;&amp; u[2] == 0 &amp;&amp; u[3] == 0 &amp;&amp; u[4] == 0);
</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>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>
<code>template &lt;typename octet_iterator&gt; uint32_t
next(octet_iterator&amp; it, octet_iterator end);</code>
<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>
<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>
<u>Return value</u>: the 32 bit representation of the processed
UTF-8 code point.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars;
int cp = next(w, twochars + 6);
assert (cp == 0x65e5);
assert (w == twochars + 3);
</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::previous</h4>
<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>
<code>template &lt;typename octet_iterator&gt; uint32_t
previous(octet_iterator&amp; it, octet_iterator pass_start);</code>
<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>
<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>
<u>Return value</u>: the 32 bit representation of the previous code
point.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars + 3;
int cp = previous (w, twochars - 1);
assert (cp == 0x65e5);
assert (w == twochars);
</pre>
<p>The primary purpose of this function is to iterate backwards
through a UTF-8 encoded string. Therefore, <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_end</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>Advances an iterator by the specified number of code points
within an UTF-8 sequence.</p>
<code>template &lt;typename octet_iterator, typename
distance_type&gt; void advance (octet_iterator&amp; it,
distance_type n, octet_iterator end);</code>
<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>
<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>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars;
advance (w, 2, twochars + 6);
assert (w == twochars + 5);
</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>Given the iterators to two UTF-8 encoded code points in a
seqence, returns the number of code points between them.</p>
<code>template &lt;typename octet_iterator&gt; typename
std::iterator_traits&lt;octet_iterator&gt;::difference_type
distance (octet_iterator first, octet_iterator last);</code>
<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>
<u>Return value</u> the distance between the iterators, in code
points.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
size_t dist = utf8::distance(twochars, twochars + 5);
assert (dist == 2);
</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>Converts a UTF-16 encoded string to UTF-8.</p>
<code>template &lt;typename u16bit_iterator, typename
octet_iterator&gt; void utf16to8 (u16bit_iterator start,
u16bit_iterator end, octet_iterator result);</code>
<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.</p>
<p>Example of use:</p>
<pre>
unsigned short utf16string[] = {0x41, 0x0448, 0x65e5, 0xd834, 0xdd1e};
vector&lt;unsigned char&gt; utf8result;
utf16to8(utf16string, utf16string + 5, back_inserter(utf8result));
assert (utf8result.size() == 10);
</pre>
<p>In case of invalid UTF-16 sequence, a
<code>utf8::invalid_utf16</code> exception is thrown.</p>
<h4>utf8::utf8to16</h4>
<p>Converts an UTF-8 encoded string to UTF-16</p>
<code>template &lt;typename u16bit_iterator, typename
octet_iterator&gt; void utf8to16 (octet_iterator start,
octet_iterator end, u16bit_iterator result);</code>
<p><code>start</code>: an iterator pointing to the beginning of the
UTF-8 encoded string to convert. &lt; br /&gt; <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.</p>
<p>Example of use:</p>
<pre>
unsigned char utf8_with_surrogates[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88,
0xf0, 0x9d, 0x84, 0x9e};
vector &lt;unsigned short&gt; utf16result;
utf8to16(utf8_with_surrogates, utf8_with_surrogates + 9, back_inserter(utf16result));
assert (utf16result.size() == 4);
assert (utf16result[2] == 0xd834);
assert (utf16result[3] == 0xdd1e);
</pre>
<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::utf32to8</h4>
<p>Converts a UTF-32 encoded string to UTF-8.</p>
<code>template &lt;typename octet_iterator, typename
u32bit_iterator&gt; void utf32to8 (u32bit_iterator start,
u32bit_iterator end, octet_iterator result);</code>
<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.</p>
<p>Example of use:</p>
<pre>
int utf32string[] = {0x448, 0x65E5, 0x10346, 0};
vector&lt;unsigned char&gt; utf8result;
utf32to8(utf32string, utf32string + 3, back_inserter(utf8result));
assert (utf8result.size() == 9);
</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>Converts a UTF-8 encoded string to UTF-32.</p>
<code>template &lt;typename octet_iterator, typename
u32bit_iterator&gt; void utf8to32 (octet_iterator start,
octet_iterator end, u32bit_iterator result);</code>
<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.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
vector&lt;int&gt; utf32result;
utf8to32(twochars, twochars + 5, back_inserter(utf32result));
assert (utf32result.size() == 2);
</pre>
<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::find_invalid</h4>
<p>Detects an invalid sequence within a UTF-8 string.</p>
<code>template &lt;typename octet_iterator&gt; octet_iterator
find_invalid(octet_iterator start, octet_iterator end);</code>
<p><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>
<u>Return value</u>: 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>
unsigned char utf_invalid[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0xfa};
unsigned char* invalid = find_invalid(utf_invalid, utf_invalid + 6);
assert (invalid == utf_invalid + 5);
</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>Checks whether a sequence of octets is a valid UTF-8 string.</p>
<code>template &lt;typename octet_iterator&gt; bool
is_valid(octet_iterator start, octet_iterator end);</code>
<p><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>
<u>Return value</u>: <code>true</code> if the sequence is a valid
UTF-8 string; <code>false</code> if not.</p>
Example of use:
<pre>
unsigned char utf_invalid[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0xfa};
bool bvalid = is_valid(utf_invalid, utf_invalid + 6);
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::is_bom</h4>
<p>Checks whether a sequence of three octets is a UTF-8 byte order
mark (BOM)</p>
<code>template &lt;typename octet_iterator&gt; bool is_bom
(octet_iterator it);</code>
<p><code>it</code> Beginning of the 3-octet sequence to check<br>
<u>Return value</u>: <code>true</code> if the sequence is UTF-8
byte order mark; <code>false</code> if not.</p>
<p>Example of use:</p>
<pre>
unsigned char byte_order_mark[] = {0xef, 0xbb, 0xbf};
bool bbom = is_bom(byte_order_mark);
assert (bbom == true);
</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>
<h3>Functions From utf8::unchecked Namespace</h3>
<h4>utf8::unchecked::append</h4>
<p>Encodes a 32 bit code point as a UTF-8 sequence of octets and
appends the sequence to a UTF-8 string.</p>
<code>template &lt;typename octet_iterator&gt; octet_iterator
append(uint32_t cp, octet_iterator result);</code>
<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>
<u>Return value</u>: An iterator pointing to the place after the
newly appended sequence.</p>
<p>Example of use:</p>
<pre>
unsigned char u[5] = {0,0,0,0,0};
unsigned char* end = unchecked::append(0x0448, u);
assert (u[0] == 0xd1 &amp;&amp; u[1] == 0x88 &amp;&amp; u[2] == 0 &amp;&amp; u[3] == 0 &amp;&amp; u[4] == 0);
</pre>
<p>This is a quicker 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>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>
<code>template &lt;typename octet_iterator&gt; uint32_t
next(octet_iterator&amp; it);</code>
<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>
<u>Return value</u>: the 32 bit representation of the processed
UTF-8 code point.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars;
int cp = unchecked::next(w);
assert (cp == 0x65e5);
assert (w == twochars + 3);
</pre>
<p>This is a quicker 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::previous</h4>
<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>
<code>template &lt;typename octet_iterator&gt; uint32_t
previous(octet_iterator&amp; it);</code>
<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>
<u>Return value</u>: the 32 bit representation of the previous code
point.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars + 3;
int cp = unchecked::previous (w);
assert (cp == 0x65e5);
assert (w == twochars);
</pre>
<p>This is a quicker 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>Advances an iterator by the specified number of code points
within an UTF-8 sequence.</p>
<code>template &lt;typename octet_iterator, typename
distance_type&gt; void advance (octet_iterator&amp; it,
distance_type n);</code>
<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>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars;
unchecked::advance (w, 2);
assert (w == twochars + 5);
</pre>
<p>This function works only "forward". In case of a negative
<code>n</code>, there is no effect.</p>
<p>This is a quicker 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>Given the iterators to two UTF-8 encoded code points in a
seqence, returns the number of code points between them.</p>
<code>template &lt;typename octet_iterator&gt; typename
std::iterator_traits&lt;octet_iterator&gt;::difference_type
distance (octet_iterator first, octet_iterator last);</code>
<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>
<u>Return value</u> the distance between the iterators, in code
points.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
size_t dist = utf8::unchecked::distance(twochars, twochars + 5);
assert (dist == 2);
</pre>
<p>This is a quicker 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>Converts a UTF-16 encoded string to UTF-8.</p>
<code>template &lt;typename u16bit_iterator, typename
octet_iterator&gt; void utf16to8 (u16bit_iterator start,
u16bit_iterator end, octet_iterator result);</code>
<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.</p>
<p>Example of use:</p>
<pre>
unsigned short utf16string[] = {0x41, 0x0448, 0x65e5, 0xd834, 0xdd1e};
vector&lt;unsigned char&gt; utf8result;
unchecked::utf16to8(utf16string, utf16string + 5, back_inserter(utf8result));
assert (utf8result.size() == 10);
</pre>
<p>This is a quicker 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>Converts an UTF-8 encoded string to UTF-16</p>
<code>template &lt;typename u16bit_iterator, typename
octet_iterator&gt; void utf8to16 (octet_iterator start,
octet_iterator end, u16bit_iterator result);</code>
<p><code>start</code>: an iterator pointing to the beginning of the
UTF-8 encoded string to convert. &lt; br /&gt; <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.</p>
<p>Example of use:</p>
<pre>
unsigned char utf8_with_surrogates[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88,
0xf0, 0x9d, 0x84, 0x9e};
vector &lt;unsigned short&gt; utf16result;
unchecked::utf8to16(utf8_with_surrogates, utf8_with_surrogates + 9, back_inserter(utf16result));
assert (utf16result.size() == 4);
assert (utf16result[2] == 0xd834);
assert (utf16result[3] == 0xdd1e);
</pre>
<p>This is a quicker 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>Converts a UTF-32 encoded string to UTF-8.</p>
<code>template &lt;typename octet_iterator, typename
u32bit_iterator&gt; void utf32to8 (u32bit_iterator start,
u32bit_iterator end, octet_iterator result);</code>
<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.</p>
<p>Example of use:</p>
<pre>
int utf32string[] = {0x448, 0x65E5, 0x10346, 0};
vector&lt;unsigned char&gt; utf8result;
utf32to8(utf32string, utf32string + 3, back_inserter(utf8result));
assert (utf8result.size() == 9);
</pre>
<p>This is a quicker 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>Converts a UTF-8 encoded string to UTF-32.</p>
<code>template &lt;typename octet_iterator, typename
u32bit_iterator&gt; void utf8to32 (octet_iterator start,
octet_iterator end, u32bit_iterator result);</code>
<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.</p>
<p>Example of use:</p>
<pre>
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
vector&lt;int&gt; utf32result;
unchecked::utf8to32(twochars, twochars + 5, back_inserter(utf32result));
assert (utf32result.size() == 2);
</pre>
<p>This is a quicker but less safe version of
<code>utf8::utf8to32</code>. It does not check for validity of the
supplied UTF-8 sequence.</p>
<h2>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"
guidline.</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><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, especially given the fact that these functions
are mature and tested in production.</li>
</ol>
<h2>Conclusion</h2>
<p>Until Unicode becomes officially recognized by the C++ Standard
Library, we need to use other means to work with UTF-8 strings.
Template functions I describe in this article may be a good step in
this direction.</p>
<h2>References</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>
</ol>
</body>
</html>

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// Copyright (c) 2006 Nemanja Trifunovic
/*
Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
execute, and transmit the Software, and to prepare derivative works of the
Software, and to permit third-parties to whom the Software is furnished to
do so, all subject to the following:
The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
works are solely in the form of machine-executable object code generated by
a source language processor.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/
#ifndef UTF8_FOR_CPP_2675DCD0_9480_4c0c_B92A_CC14C027B731
#define UTF8_FOR_CPP_2675DCD0_9480_4c0c_B92A_CC14C027B731
#include <iterator>
#include <exception>
namespace utf8
{
// The typedefs for 8-bit, 16-bit and 32-bit unsigned integers
// You may need to change them to match your system.
// These typedefs have the same names as ones from cstdint, or boost/cstdint
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;
// Exceptions that may be thrown from the library functions.
class invalid_code_point : public std::exception {
uint32_t cp;
public:
invalid_code_point(uint32_t cp) : cp(cp) {}
const char* what() { return "Invalid code point"; }
uint32_t code_point() const {return cp;}
};
class invalid_utf8 : public std::exception {
uint8_t u8;
public:
invalid_utf8 (uint8_t u) : u8(u) {}
const char* what() { return "Invalid UTF-8"; }
uint8_t utf8_octet() const {return u8;}
};
class invalid_utf16 : public std::exception {
uint16_t u16;
public:
invalid_utf16 (uint16_t u) : u16(u) {}
const char* what() { return "Invalid UTF-16"; }
uint16_t utf16_word() const {return u16;}
};
class not_enough_room : public std::exception {
public:
const char* what() { return "Not enough space"; }
};
// Unicode constants
// Leading (high) surrogates: 0xd800 - 0xdbff
// Trailing (low) surrogates: 0xdc00 - 0xdfff
const uint32_t LEAD_SURROGATE_MIN = 0xd800;
const uint32_t LEAD_SURROGATE_MAX = 0xdbff;
const uint32_t TRAIL_SURROGATE_MIN = 0xdc00;
const uint32_t TRAIL_SURROGATE_MAX = 0xdfff;
const uint32_t LEAD_OFFSET = LEAD_SURROGATE_MIN - (0x10000 >> 10);
const uint32_t SURROGATE_OFFSET = 0x10000 - (LEAD_SURROGATE_MIN << 10) - TRAIL_SURROGATE_MIN;
// Maximum valid value for a Unicode code point
const uint32_t CODE_POINT_MAX = 0x0010ffff;
// Byte order mark
const uint8_t bom[] = {0xef, 0xbb, 0xbf};
/// Helper functions - not intended to be directly called by the library users
template<typename octet_type>
inline uint8_t mask8(octet_type oc)
{
return static_cast<uint8_t>(0xff & oc);
}
template<typename u16_type>
inline uint16_t mask16(u16_type oc)
{
return static_cast<uint16_t>(0xffff & oc);
}
template<typename octet_type>
inline bool is_trail(octet_type oc)
{
return ((mask8(oc) >> 6) == 0x2);
}
template <typename u16>
inline bool is_surrogate(u16 cp)
{
return (cp >= LEAD_SURROGATE_MIN && cp <= TRAIL_SURROGATE_MAX);
}
/// The library API - functions intended to be called by the users
template <typename octet_iterator>
octet_iterator find_invalid(octet_iterator start, octet_iterator end)
{
octet_iterator result = start;
while (result != end) {
if (mask8(*result) > 0xf4)
break;
if (mask8(*result) < 0x80)
;
else if ((mask8(*result) >> 5) == 0x6) {
uint8_t lead = mask8(*result);
if (++result == end)
return (--result);
if (!is_trail(*result))
return result;
switch (lead) {
case 0xe0:
if ((mask8(*result)) < 0xa0)
return result;
break;
case 0xed:
if ((mask8(*result)) > 0x9F)
return result;
break;
case 0xf0:
if ((mask8(*result)) < 0x90)
return result;
break;
}
}
else if ((mask8(*result) >> 4) == 0xe) {
if (++result == end)
break;
if (!is_trail(*result))
break;
if (++result == end)
break;
if (!is_trail(*result))
break;
}
else if ((mask8(*result) >> 3) == 0x1e) {
if (++result == end)
break;
if (!is_trail(*result))
break;
if (++result == end)
break;
if (!is_trail(*result))
break;
if (++result == end)
break;
if (!is_trail(*result))
break;
}
else
break;
++result;
}
return result;
}
template <typename octet_iterator>
bool is_valid(octet_iterator start, octet_iterator end)
{
return (find_invalid(start, end) == end);
}
template <typename octet_iterator>
bool is_bom (octet_iterator it)
{
return (
(mask8(*it++)) == bom[0] &&
(mask8(*it++)) == bom[1] &&
(mask8(*it)) == bom[2]
);
}
template <typename octet_iterator>
octet_iterator append(uint32_t cp, octet_iterator result)
{
if (cp < 0x80) // one octet
*(result++) = static_cast<uint8_t>(cp);
else if (cp < 0x800) { // two octets
if (is_surrogate(cp))
throw invalid_code_point(cp);
*(result++) = static_cast<uint8_t>((cp >> 6) | 0xc0);
*(result++) = static_cast<uint8_t>((cp & 0x3f) | 0x80);
}
else if (cp < 0x10000) { // three octets
*(result++) = static_cast<uint8_t>((cp >> 12) | 0xe0);
*(result++) = static_cast<uint8_t>((cp >> 6) | 0x80);
*(result++) = static_cast<uint8_t>((cp & 0x3f) | 0x80);
}
else if (cp <= CODE_POINT_MAX) { // four octets
*(result++) = static_cast<uint8_t>((cp >> 18) | 0xf0);
*(result++) = static_cast<uint8_t>((cp >> 12) | 0x80);
*(result++) = static_cast<uint8_t>((cp >> 6) | 0x80);
*(result++) = static_cast<uint8_t>((cp & 0x3f) | 0x80);
}
else
throw invalid_code_point(cp);
return result;
}
template <typename octet_iterator>
uint32_t next(octet_iterator& it, octet_iterator end)
{
uint32_t cp = mask8(*it);
if (cp < 0x80)
;
else if ((mask8(*it) >> 5) == 0x6) {
if (++it != end) {
if (is_trail(*it)) {
cp = ((cp << 6) & 0x7ff) + ((*it) & 0x3f);
}
else
throw invalid_utf8 (*it);
}
else
throw not_enough_room();
}
else if ((mask8(*it) >> 4) == 0xe) {
if (++it != end) {
if (is_trail(*it)) {
cp = ((cp << 12) & 0xffff) + ((mask8(*it) << 6) & 0xfff);
if (++it != end) {
if (is_trail(*it)) {
cp += (*it) & 0x3f;
}
else
throw invalid_utf8 (*it);
}
else
throw not_enough_room();
}
else
throw invalid_utf8 (*it);
}
else
throw not_enough_room();
}
else if ((mask8(*it) >> 3) == 0x1e) {
if (++it != end) {
if (is_trail(*it)) {
cp = ((cp << 18) & 0x1fffff) + (mask8(*it) << 12) & 0x3ffff;
if (++it != end) {
if (is_trail(*it)) {
cp += (mask8(*it) << 6) & 0xfff;
if (++it != end) {
if (is_trail(*it)) {
cp += (*it) & 0x3f;
}
else
throw invalid_utf8 (*it);
}
else
throw not_enough_room();
}
else
throw invalid_utf8 (*it);
}
else
throw not_enough_room();
}
else
throw invalid_utf8 (*it);
}
else
throw not_enough_room();
}
++it;
if (cp > CODE_POINT_MAX || is_surrogate(cp))
throw invalid_code_point(cp);
return cp;
}
template <typename octet_iterator>
uint32_t previous(octet_iterator& it, octet_iterator pass_start)
{
octet_iterator end = it;
while (is_trail(*(--it)))
if (it == pass_start)
throw invalid_utf8(*it); // error - no lead byte in the sequence
octet_iterator temp = it;
return next(temp, end);
}
template <typename octet_iterator, typename distance_type>
void advance (octet_iterator& it, distance_type n, octet_iterator end)
{
for (distance_type i = 0; i < n; ++i)
next(it, end);
}
template <typename octet_iterator>
typename std::iterator_traits<octet_iterator>::difference_type
distance (octet_iterator first, octet_iterator last)
{
typename std::iterator_traits<octet_iterator>::difference_type dist;
for (dist = 0; first < last; ++dist)
next(first, last);
return dist;
}
template <typename u16bit_iterator, typename octet_iterator>
void utf16to8 (u16bit_iterator start, u16bit_iterator end, octet_iterator result)
{
while (start != end) {
uint32_t cp = mask16(*start++);
// Take care of surrogate pairs first
if (cp >= LEAD_SURROGATE_MIN && cp <= LEAD_SURROGATE_MAX) {
if (start != end) {
uint32_t trail_surrogate = mask16(*start++);
if (trail_surrogate >= TRAIL_SURROGATE_MIN && trail_surrogate <= TRAIL_SURROGATE_MAX)
cp = (cp << 10) + trail_surrogate + SURROGATE_OFFSET;
else
throw invalid_utf16(static_cast<uint16_t>(trail_surrogate));
}
else
throw invalid_utf16(static_cast<uint16_t>(*start));
}
*result = append(cp, result);
}
}
template <typename u16bit_iterator, typename octet_iterator>
void utf8to16 (octet_iterator start, octet_iterator end, u16bit_iterator result)
{
while (start != end) {
uint32_t cp = next(start, end);
if (cp > 0xffff) { //make a surrogate pair
*result++ = static_cast<uint16_t>((cp >> 10) + LEAD_OFFSET);
*result++ = static_cast<uint16_t>((cp & 0x3ff) + TRAIL_SURROGATE_MIN);
}
else
*result++ = static_cast<uint16_t>(cp);
}
}
template <typename octet_iterator, typename u32bit_iterator>
void utf32to8 (u32bit_iterator start, u32bit_iterator end, octet_iterator result)
{
while (start != end)
*result = append(*(start++), result);
}
template <typename octet_iterator, typename u32bit_iterator>
void utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result)
{
while (start < end)
(*result++) = next(start, end);
}
namespace unchecked
{
template <typename octet_iterator>
octet_iterator append(uint32_t cp, octet_iterator result)
{
if (cp < 0x80) // one octet
*(result++) = static_cast<uint8_t>(cp);
else if (cp < 0x800) { // two octets
*(result++) = static_cast<uint8_t>((cp >> 6) | 0xc0);
*(result++) = static_cast<uint8_t>((cp & 0x3f) | 0x80);
}
else if (cp < 0x10000) { // three octets
*(result++) = static_cast<uint8_t>((cp >> 12) | 0xe0);
*(result++) = static_cast<uint8_t>((cp >> 6) | 0x80);
*(result++) = static_cast<uint8_t>((cp & 0x3f) | 0x80);
}
else { // four octets
*(result++) = static_cast<uint8_t>((cp >> 18) | 0xf0);
*(result++) = static_cast<uint8_t>((cp >> 12) | 0x80);
*(result++) = static_cast<uint8_t>((cp >> 6) | 0x80);
*(result++) = static_cast<uint8_t>((cp & 0x3f) | 0x80);
}
return result;
}
template <typename octet_iterator>
uint32_t next(octet_iterator& it)
{
uint32_t cp = mask8(*it);
if (cp < 0x80)
;
else if ((mask8(*it) >> 5) == 0x6) {
it++;
cp = ((cp << 6) & 0x7ff) + ((*it) & 0x3f);
}
else if ((mask8(*it) >> 4) == 0xe) {
++it;
cp = ((cp << 12) & 0xffff) + ((mask8(*it) << 6) & 0xfff);
++it;
cp += (*it) & 0x3f;
}
else if (((*it) >> 3) == 0x1e) {
++it;
cp = ((cp << 18) & 0x1fffff) + (mask8(*it) << 12) & 0x3ffff;
++it;
cp += (mask8(*it) << 6) & 0xfff;
++it;
cp += (*it) & 0x3f;
}
++it;
return cp;
}
template <typename octet_iterator>
uint32_t previous(octet_iterator& it)
{
while (is_trail(*(--it))) ;
octet_iterator temp = it;
return next(temp);
}
template <typename octet_iterator, typename distance_type>
void advance (octet_iterator& it, distance_type n)
{
for (distance_type i = 0; i < n; ++i)
next(it);
}
template <typename octet_iterator>
uint32_t get(octet_iterator it)
{
return next(it);
}
template <typename octet_iterator>
typename std::iterator_traits<octet_iterator>::difference_type
distance (octet_iterator first, octet_iterator last)
{
typename std::iterator_traits<octet_iterator>::difference_type dist;
for (dist = 0; first < last; ++dist)
next(first);
return dist;
}
template <typename u16bit_iterator, typename octet_iterator>
void utf16to8 (u16bit_iterator start, u16bit_iterator end, octet_iterator result)
{
while (start != end) {
uint32_t cp = mask16(*start++);
// Take care of surrogate pairs first
if (cp >= LEAD_SURROGATE_MIN && cp <= LEAD_SURROGATE_MAX) {
uint32_t trail_surrogate = mask16(*start++);
cp = (cp << 10) + trail_surrogate + SURROGATE_OFFSET;
}
*result = append(cp, result);
}
}
template <typename u16bit_iterator, typename octet_iterator>
void utf8to16 (octet_iterator start, octet_iterator end, u16bit_iterator result)
{
while (start != end) {
uint32_t cp = next(start);
if (cp > 0xffff) { //make a surrogate pair
*result++ = static_cast<uint16_t>((cp >> 10) + LEAD_OFFSET);
*result++ = static_cast<uint16_t>((cp & 0x3ff) + TRAIL_SURROGATE_MIN);
}
else
*result++ = static_cast<uint16_t>(cp);
}
}
template <typename octet_iterator, typename u32bit_iterator>
void utf32to8 (u32bit_iterator start, u32bit_iterator end, octet_iterator result)
{
while (start != end)
*result = append(*(start++), result);
}
template <typename octet_iterator, typename u32bit_iterator>
void utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result)
{
while (start < end)
(*result++) = next(start);
}
} // namespace utf8::unchecked
} // namespace utf8
#endif // header guard

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UTF-8 decoder capability and stress test
----------------------------------------
Markus Kuhn <http://www.cl.cam.ac.uk/~mgk25/> - 2003-02-19
This test file can help you examine, how your UTF-8 decoder handles
various types of correct, malformed, or otherwise interesting UTF-8
sequences. This file is not meant to be a conformance test. It does
not prescribes any particular outcome and therefore there is no way to
"pass" or "fail" this test file, even though the texts suggests a
preferable decoder behaviour at some places. The aim is instead to
help you think about and test the behaviour of your UTF-8 on a
systematic collection of unusual inputs. Experience so far suggests
that most first-time authors of UTF-8 decoders find at least one
serious problem in their decoder by using this file.
The test lines below cover boundary conditions, malformed UTF-8
sequences as well as correctly encoded UTF-8 sequences of Unicode code
points that should never occur in a correct UTF-8 file.
According to ISO 10646-1:2000, sections D.7 and 2.3c, a device
receiving UTF-8 shall interpret a "malformed sequence in the same way
that it interprets a character that is outside the adopted subset" and
"characters that are not within the adopted subset shall be indicated
to the user" by a receiving device. A quite commonly used approach in
UTF-8 decoders is to replace any malformed UTF-8 sequence by a
replacement character (U+FFFD), which looks a bit like an inverted
question mark, or a similar symbol. It might be a good idea to
visually distinguish a malformed UTF-8 sequence from a correctly
encoded Unicode character that is just not available in the current
font but otherwise fully legal, even though ISO 10646-1 doesn't
mandate this. In any case, just ignoring malformed sequences or
unavailable characters does not conform to ISO 10646, will make
debugging more difficult, and can lead to user confusion.
Please check, whether a malformed UTF-8 sequence is (1) represented at
all, (2) represented by exactly one single replacement character (or
equivalent signal), and (3) the following quotation mark after an
illegal UTF-8 sequence is correctly displayed, i.e. proper
resynchronization takes place immageately after any malformed
sequence. This file says "THE END" in the last line, so if you don't
see that, your decoder crashed somehow before, which should always be
cause for concern.
All lines in this file are exactly 79 characters long (plus the line
feed). In addition, all lines end with "|", except for the two test
lines 2.1.1 and 2.2.1, which contain non-printable ASCII controls
U+0000 and U+007F. If you display this file with a fixed-width font,
these "|" characters should all line up in column 79 (right margin).
This allows you to test quickly, whether your UTF-8 decoder finds the
correct number of characters in every line, that is whether each
malformed sequences is replaced by a single replacement character.
Note that as an alternative to the notion of malformed sequence used
here, it is also a perfectly acceptable (and in some situations even
preferable) solution to represent each individual byte of a malformed
sequence by a replacement character. If you follow this strategy in
your decoder, then please ignore the "|" column.
Here come the tests: |
|
1 Some correct UTF-8 text |
|
You should see the Greek word 'kosme': "κόσμε" |
|
2 Boundary condition test cases |
|
2.1 First possible sequence of a certain length |
|
2.1.1 1 byte (U-00000000): ""
2.1.2 2 bytes (U-00000080): "€" |
2.1.3 3 bytes (U-00000800): "ࠀ" |
2.1.4 4 bytes (U-00010000): "𐀀" |
2.1.5 5 bytes (U-00200000): "?" |
2.1.6 6 bytes (U-04000000): "?" |
|
2.2 Last possible sequence of a certain length |
|
2.2.1 1 byte (U-0000007F): ""
2.2.2 2 bytes (U-000007FF): "߿" |
2.2.3 3 bytes (U-0000FFFF): "?" |
2.2.4 4 bytes (U-001FFFFF): "?" |
2.2.5 5 bytes (U-03FFFFFF): "?" |
2.2.6 6 bytes (U-7FFFFFFF): "?" |
|
2.3 Other boundary conditions |
|
2.3.1 U-0000D7FF = ed 9f bf = "퟿" |
2.3.2 U-0000E000 = ee 80 80 = "" |
2.3.3 U-0000FFFD = ef bf bd = "<22>" |
2.3.4 U-0010FFFF = f4 8f bf bf = "􏿿" |
2.3.5 U-00110000 = f4 90 80 80 = "?" |
|
3 Malformed sequences |
|
3.1 Unexpected continuation bytes |
|
Each unexpected continuation byte should be separately signalled as a |
malformed sequence of its own. |
|
3.1.1 First continuation byte 0x80: "?" |
3.1.2 Last continuation byte 0xbf: "?" |
|
3.1.3 2 continuation bytes: "??" |
3.1.4 3 continuation bytes: "???" |
3.1.5 4 continuation bytes: "????" |
3.1.6 5 continuation bytes: "?????" |
3.1.7 6 continuation bytes: "??????" |
3.1.8 7 continuation bytes: "???????" |
|
3.1.9 Sequence of all 64 possible continuation bytes (0x80-0xbf): |
|
"???????????????? |
???????????????? |
???????????????? |
????????????????" |
|
3.2 Lonely start characters |
|
3.2.1 All 32 first bytes of 2-byte sequences (0xc0-0xdf), |
each followed by a space character: |
|
"?? àĠŠƠǠȠɠʠˠ̠͠ΠϠ |
РѠҠӠԠՠ֠נؠ٠ڠ۠ܠݠޠߠ" |
|
3.2.2 All 16 first bytes of 3-byte sequences (0xe0-0xef), |
each followed by a space character: |
|
"ࠡ ⠣ 䠥 栧 蠩 ꠫ 젭  " |
|
3.2.3 All 8 first bytes of 4-byte sequences (0xf0-0xf7), |
each followed by a space character: |
|
"𠱠򠳠??" |
|
3.2.4 All 4 first bytes of 5-byte sequences (0xf8-0xfb), |
each followed by a space character: |
|
"? ? |
|
3.2.5 All 2 first bytes of 6-byte sequences (0xfc-0xfd), |
each followed by a space character: |
|
"? |
|
3.3 Sequences with last continuation byte missing |
|
All bytes of an incomplete sequence should be signalled as a single |
malformed sequence, i.e., you should see only a single replacement |
character in each of the next 10 tests. (Characters as in section 2) |
|
3.3.1 2-byte sequence with last byte missing (U+0000): "? |
3.3.2 3-byte sequence with last byte missing (U+0000): "? |
3.3.3 4-byte sequence with last byte missing (U+0000): "? |
3.3.4 5-byte sequence with last byte missing (U+0000): "? |
3.3.5 6-byte sequence with last byte missing (U+0000): "? |
3.3.6 2-byte sequence with last byte missing (U-000007FF): "ߢ |
3.3.7 3-byte sequence with last byte missing (U-0000FFFF): "￢ |
3.3.8 4-byte sequence with last byte missing (U-001FFFFF): "? |
3.3.9 5-byte sequence with last byte missing (U-03FFFFFF): "? |
3.3.10 6-byte sequence with last byte missing (U-7FFFFFFF): "? |
|
3.4 Concatenation of incomplete sequences |
|
All the 10 sequences of 3.3 concatenated, you should see 10 malformed |
sequences being signalled: |
|
"???????????????" |
|
3.5 Impossible bytes |
|
The following two bytes cannot appear in a correct UTF-8 string |
|
3.5.1 fe = "? |
3.5.2 ff = "? |
3.5.3 fe fe ff ff = "? |
|
4 Overlong sequences |
|
The following sequences are not malformed according to the letter of |
the Unicode 2.0 standard. However, they are longer then necessary and |
a correct UTF-8 encoder is not allowed to produce them. A "safe UTF-8 |
decoder" should reject them just like malformed sequences for two |
reasons: (1) It helps to debug applications if overlong sequences are |
not treated as valid representations of characters, because this helps |
to spot problems more quickly. (2) Overlong sequences provide |
alternative representations of characters, that could maliciously be |
used to bypass filters that check only for ASCII characters. For |
instance, a 2-byte encoded line feed (LF) would not be caught by a |
line counter that counts only 0x0a bytes, but it would still be |
processed as a line feed by an unsafe UTF-8 decoder later in the |
pipeline. From a security point of view, ASCII compatibility of UTF-8 |
sequences means also, that ASCII characters are *only* allowed to be |
represented by ASCII bytes in the range 0x00-0x7f. To ensure this |
aspect of ASCII compatibility, use only "safe UTF-8 decoders" that |
reject overlong UTF-8 sequences for which a shorter encoding exists. |
|
4.1 Examples of an overlong ASCII character |
|
With a safe UTF-8 decoder, all of the following five overlong |
representations of the ASCII character slash ("/") should be rejected |
like a malformed UTF-8 sequence, for instance by substituting it with |
a replacement character. If you see a slash below, you do not have a |
safe UTF-8 decoder! |
|
4.1.1 U+002F = c0 af = "?" |
4.1.2 U+002F = e0 80 af = "?" |
4.1.3 U+002F = f0 80 80 af = "?" |
4.1.4 U+002F = f8 80 80 80 af = "?" |
4.1.5 U+002F = fc 80 80 80 80 af = "?" |
|
4.2 Maximum overlong sequences |
|
Below you see the highest Unicode value that is still resulting in an |
overlong sequence if represented with the given number of bytes. This |
is a boundary test for safe UTF-8 decoders. All five characters should |
be rejected like malformed UTF-8 sequences. |
|
4.2.1 U-0000007F = c1 bf = "?" |
4.2.2 U-000007FF = e0 9f bf = "?" |
4.2.3 U-0000FFFF = f0 8f bf bf = "?" |
4.2.4 U-001FFFFF = f8 87 bf bf bf = "?" |
4.2.5 U-03FFFFFF = fc 83 bf bf bf bf = "?" |
|
4.3 Overlong representation of the NUL character |
|
The following five sequences should also be rejected like malformed |
UTF-8 sequences and should not be treated like the ASCII NUL |
character. |
|
4.3.1 U+0000 = c0 80 = "?" |
4.3.2 U+0000 = e0 80 80 = "?" |
4.3.3 U+0000 = f0 80 80 80 = "?" |
4.3.4 U+0000 = f8 80 80 80 80 = "?" |
4.3.5 U+0000 = fc 80 80 80 80 80 = "?" |
|
5 Illegal code positions |
|
The following UTF-8 sequences should be rejected like malformed |
sequences, because they never represent valid ISO 10646 characters and |
a UTF-8 decoder that accepts them might introduce security problems |
comparable to overlong UTF-8 sequences. |
|
5.1 Single UTF-16 surrogates |
|
5.1.1 U+D800 = ed a0 80 = "<22><><EFBFBD>" |
5.1.2 U+DB7F = ed ad bf = "<22><><EFBFBD>" |
5.1.3 U+DB80 = ed ae 80 = "<22><><EFBFBD>" |
5.1.4 U+DBFF = ed af bf = "<22><><EFBFBD>" |
5.1.5 U+DC00 = ed b0 80 = "<22><><EFBFBD>" |
5.1.6 U+DF80 = ed be 80 = "<22><><EFBFBD>" |
5.1.7 U+DFFF = ed bf bf = "<22><><EFBFBD>" |
|
5.2 Paired UTF-16 surrogates |
|
5.2.1 U+D800 U+DC00 = ed a0 80 ed b0 80 = "𐀀" |
5.2.2 U+D800 U+DFFF = ed a0 80 ed bf bf = "𐏿" |
5.2.3 U+DB7F U+DC00 = ed ad bf ed b0 80 = "󯰀" |
5.2.4 U+DB7F U+DFFF = ed ad bf ed bf bf = "󯿿" |
5.2.5 U+DB80 U+DC00 = ed ae 80 ed b0 80 = "󰀀" |
5.2.6 U+DB80 U+DFFF = ed ae 80 ed bf bf = "󰏿" |
5.2.7 U+DBFF U+DC00 = ed af bf ed b0 80 = "􏰀" |
5.2.8 U+DBFF U+DFFF = ed af bf ed bf bf = "􏿿" |
|
5.3 Other illegal code positions |
|
5.3.1 U+FFFE = ef bf be = "?" |
5.3.2 U+FFFF = ef bf bf = "?" |
|
THE END |

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#include <cassert>
#include <vector>
#include <iterator>
#include "utf8.h"
using namespace utf8;
using namespace std;
int main()
{
//append
unsigned char u[5] = {0,0,0,0,0};
unsigned char* end = append(0x0448, u);
assert (u[0] == 0xd1 && u[1] == 0x88 && u[2] == 0 && u[3] == 0 && u[4] == 0);
end = append(0x65e5, u);
assert (u[0] == 0xe6 && u[1] == 0x97 && u[2] == 0xa5 && u[3] == 0 && u[4] == 0);
end = append(0x10346, u);
assert (u[0] == 0xf0 && u[1] == 0x90 && u[2] == 0x8d && u[3] == 0x86 && u[4] == 0);
//next
unsigned char twochars[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0x0};
unsigned char* w = twochars;
int cp = next(w, twochars + 6);
assert (cp == 0x65e5);
assert (w == twochars + 3);
//previous
cp = previous (w, twochars - 1);
assert (cp == 0x65e5);
assert (w == twochars);
// advance
w = twochars;
advance (w, 2, twochars + 6);
assert (w == twochars + 5);
// distance
size_t dist = utf8::distance(twochars, twochars + 5);
assert (dist == 2);
// utf32to8
int utf32string[] = {0x448, 0x65E5, 0x10346, 0};
vector<unsigned char> utf8result;
utf32to8(utf32string, utf32string + 3, back_inserter(utf8result));
assert (utf8result.size() == 9);
//utf8to32
vector<int> utf32result;
utf8to32(twochars, twochars + 5, back_inserter(utf32result));
assert (utf32result.size() == 2);
//utf16to8
unsigned short utf16string[] = {0x41, 0x0448, 0x65e5, 0xd834, 0xdd1e};
utf8result.clear();
utf16to8(utf16string, utf16string + 5, back_inserter(utf8result));
assert (utf8result.size() == 10);
//utf8to16
unsigned char utf8_with_surrogates[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88,
0xf0, 0x9d, 0x84, 0x9e};
vector <unsigned short> utf16result;
utf8to16(utf8_with_surrogates, utf8_with_surrogates + 9, back_inserter(utf16result));
assert (utf16result.size() == 4);
assert (utf16result[2] == 0xd834);
assert (utf16result[3] == 0xdd1e);
//find_invalid
unsigned char utf_invalid[] = {0xE6, 0x97, 0xA5, 0xd1, 0x88, 0xfa};
unsigned char* invalid = find_invalid(utf_invalid, utf_invalid + 6);
assert (invalid == utf_invalid + 5);
//is_valid
bool bvalid = is_valid(utf_invalid, utf_invalid + 6);
assert (bvalid == false);
bvalid = is_valid(utf8_with_surrogates, utf8_with_surrogates + 9);
assert (bvalid == true);
//is_bom
unsigned char byte_order_mark[] = {0xef, 0xbb, 0xbf};
bool bbom = is_bom(byte_order_mark);
assert (bbom == true);
//////////////////////////////////////////////////////////
//// Unchecked variants
//////////////////////////////////////////////////////////
//append
memset(u, 0, 5);
end = unchecked::append(0x0448, u);
assert (u[0] == 0xd1 && u[1] == 0x88 && u[2] == 0 && u[3] == 0 && u[4] == 0);
end = unchecked::append(0x65e5, u);
assert (u[0] == 0xe6 && u[1] == 0x97 && u[2] == 0xa5 && u[3] == 0 && u[4] == 0);
end = unchecked::append(0x10346, u);
assert (u[0] == 0xf0 && u[1] == 0x90 && u[2] == 0x8d && u[3] == 0x86 && u[4] == 0);
//next
w = twochars;
cp = unchecked::next(w);
assert (cp == 0x65e5);
assert (w == twochars + 3);
//previous
cp = unchecked::previous (w);
assert (cp == 0x65e5);
assert (w == twochars);
// advance
w = twochars;
unchecked::advance (w, 2);
assert (w == twochars + 5);
// distance
dist = unchecked::distance(twochars, twochars + 5);
assert (dist == 2);
// utf32to8
utf8result.clear();
unchecked::utf32to8(utf32string, utf32string + 3, back_inserter(utf8result));
assert (utf8result.size() == 9);
//utf8to32
utf32result.clear();
unchecked::utf8to32(twochars, twochars + 5, back_inserter(utf32result));
assert (utf32result.size() == 2);
//utf16to8
utf8result.clear();
unchecked::utf16to8(utf16string, utf16string + 5, back_inserter(utf8result));
assert (utf8result.size() == 10);
//utf8to16
utf16result.clear();
unchecked::utf8to16(utf8_with_surrogates, utf8_with_surrogates + 9, back_inserter(utf16result));
assert (utf16result.size() == 4);
assert (utf16result[2] == 0xd834);
assert (utf16result[3] == 0xdd1e);
}