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.
In order to easily handle UTF-8 encoded Unicode strings, I have come 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.
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 Unicode Home Page 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.
To illustrate the use of this utf8 library, we shall open a file containing UTF-8
encoded text, check whether it starts with a byte order mark, read each line into a
std::string, check it for validity, convert the text to UTF-16, and
back to UTF-8:
#include <fstream> #include <iostream> #include <string> #include <vector> #include "utf8.h" using namespace std; int main() { if (argc != 2) { cout << "\nUsage: docsample filename\n"; return 0; } const char* test_file_path = argv[1]; // Open the test file (must be UTF-8 encoded) ifstream fs8(test_file_path); if (!fs8.is_open()) { cout << "Could not open " << test_file_path << endl; return 0; } // Read the first line of the file unsigned line_count = 1; string line; if (!getline(fs8, line)) return 0; // Look for utf-8 byte-order mark at the beginning if (line.size() > 2) { if (utf8::is_bom(line.c_str())) cout << "There is a byte order mark at the beginning of the file\n"; } // Play with all the lines in the file do { // check for invalid utf-8 (for a simple yes/no check, there is also utf8::is_valid function) string::iterator end_it = utf8::find_invalid(line.begin(), line.end()); if (end_it != line.end()) { cout << "Invalid UTF-8 encoding detected at line " << line_count << "\n"; cout << "This part is fine: " << string(line.begin(), end_it) << "\n"; } // Get the line length (at least for the valid part) int length = utf8::distance(line.begin(), end_it); cout << "Length of line " << line_count << " is " << length << "\n"; // Convert it to utf-16 vector<unsigned short> utf16line; utf8::utf8to16(line.begin(), end_it, back_inserter(utf16line)); // And back to utf-8 string utf8line; utf8::utf16to8(utf16line.begin(), utf16line.end(), back_inserter(utf8line)); // Confirm that the conversion went OK: if (utf8line != string(line.begin(), end_it)) cout << "Error in UTF-16 conversion at line: " << line_count << "\n"; getline(fs8, line); line_count++; } while (!fs8.eof()); return 0; }
In the previous code sample, we have seen the use of the following functions from
utf8 namespace: first we used is_bom function to detect
UTF-8 byte order mark at the beginning of the file; then for each line we performed
a detection of invalid UTF-8 sequences with find_invalid; the number
of characters (more precisely - the number of Unicode code points) in each line was
determined with a use of utf8::distance; finally, we have converted
each line to UTF-16 encoding with utf8to16 and back to UTF-8 with
utf16to8.
Encodes a 32 bit code point as a UTF-8 sequence of octets and appends the sequence to a UTF-8 string.
template <typename octet_iterator> octet_iterator append(uint32_t cp, octet_iterator result);
cp: A 32 bit integer representing a code point to append to the
sequence.
result: An output iterator to the place in the sequence where to
append the code point.
Return value: An iterator pointing to the place
after the newly appended sequence.
Example of use:
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);
Note that append 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, append can add anywhere between 1 and 4
octets to the sequence. In practice, you would most often want to use
std::back_inserter to ensure that the necessary memory is allocated.
In case of an invalid code point, a utf8::invalid_code_point exception
is thrown.
Given the iterator to the beginning of the UTF-8 sequence, it returns the code point and moves the iterator to the next position.
template <typename octet_iterator> uint32_t next(octet_iterator& it, octet_iterator end);
it: 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.
end: end of the UTF-8 sequence to be processed. If it
gets equal to end during the extraction of a code point, an
utf8::not_enough_room exception is thrown.
Return value: the 32 bit representation of the
processed UTF-8 code point.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; char* w = twochars; int cp = next(w, twochars + 6); assert (cp == 0x65e5); assert (w == twochars + 3);
This function is typically used to iterate through a UTF-8 encoded string.
In case of an invalid UTF-8 seqence, a utf8::invalid_utf8 exception is
thrown.
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.
template <typename octet_iterator> uint32_t prior(octet_iterator& it, octet_iterator start);
it: 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.
start: 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.
Return value: the 32 bit representation of the
previous code point.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; unsigned char* w = twochars + 3; int cp = prior (w, twochars); assert (cp == 0x65e5); assert (w == twochars);
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 utf8::next is faster. The second purpose is to find a beginning
of a UTF-8 sequence if we have a random position within a string.
it will typically point to the beginning of
a code point, and start will point to the
beginning of the string to ensure we don't go backwards too far. it 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.
In case pass_end is reached before a UTF-8 lead octet is hit, or if an
invalid UTF-8 sequence is started by the lead octet, an invalid_utf8
exception is thrown.
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.
template <typename octet_iterator> uint32_t previous(octet_iterator& it, octet_iterator pass_start);
it: 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.
pass_start: 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.
Return value: the 32 bit representation of the
previous code point.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; unsigned char* w = twochars + 3; int cp = previous (w, twochars - 1); assert (cp == 0x65e5); assert (w == twochars);
utf8::previous is deprecated, and utf8::prior should
be used instead, although the existing code can continue using this function.
The problem is the parameter pass_start 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.
it will typically point to the beginning of
a code point, and pass_start will point to the octet just before the
beginning of the string to ensure we don't go backwards too far. it 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.
In case pass_end is reached before a UTF-8 lead octet is hit, or if an
invalid UTF-8 sequence is started by the lead octet, an invalid_utf8
exception is thrown
Advances an iterator by the specified number of code points within an UTF-8 sequence.
template <typename octet_iterator, typename distance_type> void advance (octet_iterator& it, distance_type n, octet_iterator end);
it: 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.
n: a positive integer that shows how many code points we want to
advance.
end: end of the UTF-8 sequence to be processed. If it
gets equal to end during the extraction of a code point, an
utf8::not_enough_room exception is thrown.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; unsigned char* w = twochars; advance (w, 2, twochars + 6); assert (w == twochars + 5);
This function works only "forward". In case of a negative n, there is
no effect.
In case of an invalid code point, a utf8::invalid_code_point exception
is thrown.
Given the iterators to two UTF-8 encoded code points in a seqence, returns the number of code points between them.
template <typename octet_iterator> typename std::iterator_traits<octet_iterator>::difference_type distance (octet_iterator first, octet_iterator last);
first: an iterator to a beginning of a UTF-8 encoded code point.
last: 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.
Return value the distance between the iterators,
in code points.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; size_t dist = utf8::distance(twochars, twochars + 5); assert (dist == 2);
This function is used to find the length (in code points) of a UTF-8 encoded
string. The reason it is called distance, rather than, say,
length is mainly because developers are used that length 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 std::distance algorithm.
In case of an invalid UTF-8 seqence, a utf8::invalid_utf8 exception is
thrown. If last does not point to the past-of-end of a UTF-8 seqence,
a utf8::not_enough_room exception is thrown.
Converts a UTF-16 encoded string to UTF-8.
template <typename u16bit_iterator, typename octet_iterator> octet_iterator utf16to8 (u16bit_iterator start, u16bit_iterator end, octet_iterator result);
start: an iterator pointing to the beginning of the UTF-16 encoded
string to convert.
end: an iterator pointing to pass-the-end of the UTF-16 encoded
string to convert.
result: an output iterator to the place in the UTF-8 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-8 string.
Example of use:
unsigned short utf16string[] = {0x41, 0x0448, 0x65e5, 0xd834, 0xdd1e}; vector<unsigned char> utf8result; utf16to8(utf16string, utf16string + 5, back_inserter(utf8result)); assert (utf8result.size() == 10);
In case of invalid UTF-16 sequence, a utf8::invalid_utf16 exception is
thrown.
Converts an UTF-8 encoded string to UTF-16
template <typename u16bit_iterator, typename octet_iterator> u16bit_iterator utf8to16 (octet_iterator start, octet_iterator end, u16bit_iterator result);
start: an iterator pointing to the beginning of the UTF-8 encoded
string to convert. < br /> end: an iterator pointing to
pass-the-end of the UTF-8 encoded string to convert.
result: an output iterator to the place in the UTF-16 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-16 string.
Example of use:
char utf8_with_surrogates[] = "\xe6\x97\xa5\xd1\x88\xf0\x9d\x84\x9e"; 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);
In case of an invalid UTF-8 seqence, a utf8::invalid_utf8 exception is
thrown. If end does not point to the past-of-end of a UTF-8 seqence, a
utf8::not_enough_room exception is thrown.
Converts a UTF-32 encoded string to UTF-8.
template <typename octet_iterator, typename u32bit_iterator> octet_iterator utf32to8 (u32bit_iterator start, u32bit_iterator end, octet_iterator result);
start: an iterator pointing to the beginning of the UTF-32 encoded
string to convert.
end: an iterator pointing to pass-the-end of the UTF-32 encoded
string to convert.
result: an output iterator to the place in the UTF-8 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-8 string.
Example of use:
int utf32string[] = {0x448, 0x65E5, 0x10346, 0}; vector<unsigned char> utf8result; utf32to8(utf32string, utf32string + 3, back_inserter(utf8result)); assert (utf8result.size() == 9);
In case of invalid UTF-32 string, a utf8::invalid_code_point exception
is thrown.
Converts a UTF-8 encoded string to UTF-32.
template <typename octet_iterator, typename u32bit_iterator> u32bit_iterator utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result);
start: an iterator pointing to the beginning of the UTF-8 encoded
string to convert.
end: an iterator pointing to pass-the-end of the UTF-8 encoded string
to convert.
result: an output iterator to the place in the UTF-32 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-32 string.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; vector<int> utf32result; utf8to32(twochars, twochars + 5, back_inserter(utf32result)); assert (utf32result.size() == 2);
In case of an invalid UTF-8 seqence, a utf8::invalid_utf8 exception is
thrown. If end does not point to the past-of-end of a UTF-8 seqence, a
utf8::not_enough_room exception is thrown.
Detects an invalid sequence within a UTF-8 string.
template <typename octet_iterator> octet_iterator find_invalid(octet_iterator start, octet_iterator end);
start: an iterator pointing to the beginning of the UTF-8 string to
test for validity.
end: an iterator pointing to pass-the-end of the UTF-8 string to test
for validity.
Return value: an iterator pointing to the first
invalid octet in the UTF-8 string. In case none were found, equals
end.
Example of use:
char utf_invalid[] = "\xe6\x97\xa5\xd1\x88\xfa"; char* invalid = find_invalid(utf_invalid, utf_invalid + 6); assert (invalid == utf_invalid + 5);
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 unchecked operations on it.
Checks whether a sequence of octets is a valid UTF-8 string.
template <typename octet_iterator> bool is_valid(octet_iterator start, octet_iterator end);
start: an iterator pointing to the beginning of the UTF-8 string to
test for validity.
end: an iterator pointing to pass-the-end of the UTF-8 string to test
for validity.
Return value: true if the sequence
is a valid UTF-8 string; false if not.
char utf_invalid[] = "\xe6\x97\xa5\xd1\x88\xfa"; bool bvalid = is_valid(utf_invalid, utf_invalid + 6); assert (bvalid == false);
is_valid is a shorthand for find_invalid(start, end) ==
end;. 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.
Replaces all invalid UTF-8 sequences within a string with a replacement marker.
template <typename octet_iterator, typename output_iterator> output_iterator replace_invalid(octet_iterator start, octet_iterator end, output_iterator out, uint32_t replacement); template <typename octet_iterator, typename output_iterator> output_iterator replace_invalid(octet_iterator start, octet_iterator end, output_iterator out);
start: an iterator pointing to the beginning of the UTF-8 string to
look for invalid UTF-8 sequences.
end: an iterator pointing to pass-the-end of the UTF-8 string to look
for invalid UTF-8 sequences.
out: An output iterator to the range where the result of replacement
is stored.
replacement: A Unicode code point for the replacement marker. The
version without this parameter assumes the value 0xfffd
Return value: An iterator pointing to the place
after the UTF-8 string with replaced invalid sequences.
Example of use:
char invalid_sequence[] = "a\x80\xe0\xa0\xc0\xaf\xed\xa0\x80z"; vector<char> replace_invalid_result; replace_invalid (invalid_sequence, invalid_sequence + sizeof(invalid_sequence), back_inserter(replace_invalid_result), '?'); bvalid = is_valid(replace_invalid_result.begin(), replace_invalid_result.end()); assert (bvalid); char* fixed_invalid_sequence = "a????z"; assert (std::equal(replace_invalid_result.begin(), replace_invalid_result.end(), fixed_invalid_sequence));
replace_invalid 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, out must not
be in the [start, end] range.
If end does not point to the past-of-end of a UTF-8 sequence, a
utf8::not_enough_room exception is thrown.
Checks whether a sequence of three octets is a UTF-8 byte order mark (BOM)
template <typename octet_iterator> bool is_bom (octet_iterator it);
it: beginning of the 3-octet sequence to check
Return value: true if the sequence
is UTF-8 byte order mark; false if not.
Example of use:
unsigned char byte_order_mark[] = {0xef, 0xbb, 0xbf}; bool bbom = is_bom(byte_order_mark); assert (bbom == true);
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.
Adapts the underlying octet iterator to iterate over the sequence of code points, rather than raw octets.
template <typename octet_iterator> class iterator;
iterator(); octet_iterator is
constructed with its default constructor.
explicit iterator (const octet_iterator& octet_it,
const octet_iterator& range_start,
const octet_iterator& range_end); octet_iterator with octet_it
and sets the range in which the iterator is considered valid.
octet_iterator base () const; octet_iterator.
uint32_t operator * () const; octet_iterator is pointing to and returns the code point.
bool operator == (const iterator& rhs)
const; bool operator != (const iterator& rhs)
const; iterator& operator ++ (); iterator operator ++ (int); iterator& operator -- (); iterator operator -- (int); Example of use:
char* threechars = "\xf0\x90\x8d\x86\xe6\x97\xa5\xd1\x88"; utf8::iterator<char*> it(threechars, threechars, threechars + 9); utf8::iterator<char*> it2 = it; assert (it2 == it); assert (*it == 0x10346); assert (*(++it) == 0x65e5); assert ((*it++) == 0x65e5); assert (*it == 0x0448); assert (it != it2); utf8::iterator<char*> endit (threechars + 9, threechars, threechars + 9); assert (++it == endit); assert (*(--it) == 0x0448); assert ((*it--) == 0x0448); assert (*it == 0x65e5); assert (--it == utf8::iterator<char*>(threechars, threechars, threechars + 9)); assert (*it == 0x10346);
The purpose of utf8::iterator 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
utf8::next() and utf8::prior() functions.
Note that utf8::iterator 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 begin and end, i.e.:
std::string s = "example";
utf8::iterator i (s.begin(), s.begin(), s.end());
Encodes a 32 bit code point as a UTF-8 sequence of octets and appends the sequence to a UTF-8 string.
template <typename octet_iterator> octet_iterator append(uint32_t cp, octet_iterator result);
cp: A 32 bit integer representing a code point to append to the
sequence.
result: An output iterator to the place in the sequence where to
append the code point.
Return value: An iterator pointing to the place
after the newly appended sequence.
Example of use:
unsigned char u[5] = {0,0,0,0,0}; unsigned char* end = unchecked::append(0x0448, u); assert (u[0] == 0xd1 && u[1] == 0x88 && u[2] == 0 && u[3] == 0 && u[4] == 0);
This is a faster but less safe version of utf8::append. It does not
check for validity of the supplied code point, and may produce an invalid UTF-8
sequence.
Given the iterator to the beginning of a UTF-8 sequence, it returns the code point and moves the iterator to the next position.
template <typename octet_iterator> uint32_t next(octet_iterator& it);
it: 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.
Return value: the 32 bit representation of the
processed UTF-8 code point.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; char* w = twochars; int cp = unchecked::next(w); assert (cp == 0x65e5); assert (w == twochars + 3);
This is a faster but less safe version of utf8::next. It does not
check for validity of the supplied UTF-8 sequence.
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.
template <typename octet_iterator> uint32_t prior(octet_iterator& it);
it: 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.
Return value: the 32 bit representation of the
previous code point.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; char* w = twochars + 3; int cp = unchecked::prior (w); assert (cp == 0x65e5); assert (w == twochars);
This is a faster but less safe version of utf8::prior. It does not
check for validity of the supplied UTF-8 sequence and offers no boundary checking.
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.
template <typename octet_iterator> uint32_t previous(octet_iterator& it);
it: 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.
Return value: the 32 bit representation of the
previous code point.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; char* w = twochars + 3; int cp = unchecked::previous (w); assert (cp == 0x65e5); assert (w == twochars);
The reason this function is deprecated is just the consistency with the "checked"
versions, where prior should be used instead of previous.
In fact, unchecked::previous behaves exactly the same as
unchecked::prior
This is a faster but less safe version of utf8::previous. It does not
check for validity of the supplied UTF-8 sequence and offers no boundary checking.
Advances an iterator by the specified number of code points within an UTF-8 sequence.
template <typename octet_iterator, typename distance_type> void advance (octet_iterator& it, distance_type n);
it: 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.
n: a positive integer that shows how many code points we want to
advance.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; char* w = twochars; unchecked::advance (w, 2); assert (w == twochars + 5);
This function works only "forward". In case of a negative n, there is
no effect.
This is a faster but less safe version of utf8::advance. It does not
check for validity of the supplied UTF-8 sequence and offers no boundary checking.
Given the iterators to two UTF-8 encoded code points in a seqence, returns the number of code points between them.
template <typename octet_iterator> typename std::iterator_traits<octet_iterator>::difference_type distance (octet_iterator first, octet_iterator last);
first: an iterator to a beginning of a UTF-8 encoded code point.
last: 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.
Return value the distance between the iterators,
in code points.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; size_t dist = utf8::unchecked::distance(twochars, twochars + 5); assert (dist == 2);
This is a faster but less safe version of utf8::distance. It does not
check for validity of the supplied UTF-8 sequence.
Converts a UTF-16 encoded string to UTF-8.
template <typename u16bit_iterator, typename octet_iterator> octet_iterator utf16to8 (u16bit_iterator start, u16bit_iterator end, octet_iterator result);
start: an iterator pointing to the beginning of the UTF-16 encoded
string to convert.
end: an iterator pointing to pass-the-end of the UTF-16 encoded
string to convert.
result: an output iterator to the place in the UTF-8 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-8 string.
Example of use:
unsigned short utf16string[] = {0x41, 0x0448, 0x65e5, 0xd834, 0xdd1e}; vector<unsigned char> utf8result; unchecked::utf16to8(utf16string, utf16string + 5, back_inserter(utf8result)); assert (utf8result.size() == 10);
This is a faster but less safe version of utf8::utf16to8. It does not
check for validity of the supplied UTF-16 sequence.
Converts an UTF-8 encoded string to UTF-16
template <typename u16bit_iterator, typename octet_iterator> u16bit_iterator utf8to16 (octet_iterator start, octet_iterator end, u16bit_iterator result);
start: an iterator pointing to the beginning of the UTF-8 encoded
string to convert. < br /> end: an iterator pointing to
pass-the-end of the UTF-8 encoded string to convert.
result: an output iterator to the place in the UTF-16 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-16 string.
Example of use:
char utf8_with_surrogates[] = "\xe6\x97\xa5\xd1\x88\xf0\x9d\x84\x9e"; vector <unsigned short> 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);
This is a faster but less safe version of utf8::utf8to16. It does not
check for validity of the supplied UTF-8 sequence.
Converts a UTF-32 encoded string to UTF-8.
template <typename octet_iterator, typename u32bit_iterator> octet_iterator utf32to8 (u32bit_iterator start, u32bit_iterator end, octet_iterator result);
start: an iterator pointing to the beginning of the UTF-32 encoded
string to convert.
end: an iterator pointing to pass-the-end of the UTF-32 encoded
string to convert.
result: an output iterator to the place in the UTF-8 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-8 string.
Example of use:
int utf32string[] = {0x448, 0x65e5, 0x10346, 0}; vector<unsigned char> utf8result; utf32to8(utf32string, utf32string + 3, back_inserter(utf8result)); assert (utf8result.size() == 9);
This is a faster but less safe version of utf8::utf32to8. It does not
check for validity of the supplied UTF-32 sequence.
Converts a UTF-8 encoded string to UTF-32.
template <typename octet_iterator, typename u32bit_iterator> u32bit_iterator utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result);
start: an iterator pointing to the beginning of the UTF-8 encoded
string to convert.
end: an iterator pointing to pass-the-end of the UTF-8 encoded string
to convert.
result: an output iterator to the place in the UTF-32 string where to
append the result of conversion.
Return value: An iterator pointing to the place
after the appended UTF-32 string.
Example of use:
char* twochars = "\xe6\x97\xa5\xd1\x88"; vector<int> utf32result; unchecked::utf8to32(twochars, twochars + 5, back_inserter(utf32result)); assert (utf32result.size() == 2);
This is a faster but less safe version of utf8::utf8to32. It does not
check for validity of the supplied UTF-8 sequence.
Adapts the underlying octet iterator to iterate over the sequence of code points, rather than raw octets.
template <typename octet_iterator> class iterator;
iterator(); octet_iterator is
constructed with its default constructor.
explicit iterator (const octet_iterator& octet_it);
octet_iterator with octet_it
octet_iterator base () const; octet_iterator.
uint32_t operator * () const; octet_iterator is pointing to and returns the code point.
bool operator == (const iterator& rhs)
const; bool operator != (const iterator& rhs)
const; iterator& operator ++ (); iterator operator ++ (int); iterator& operator -- (); iterator operator -- (int); Example of use:
char* threechars = "\xf0\x90\x8d\x86\xe6\x97\xa5\xd1\x88"; utf8::unchecked::iterator<char*> un_it(threechars); utf8::unchecked::iterator<char*> un_it2 = un_it; assert (un_it2 == un_it); assert (*un_it == 0x10346); assert (*(++un_it) == 0x65e5); assert ((*un_it++) == 0x65e5); assert (*un_it == 0x0448); assert (un_it != un_it2); utf8::::unchecked::iterator<char*> un_endit (threechars + 9); assert (++un_it == un_endit); assert (*(--un_it) == 0x0448); assert ((*un_it--) == 0x0448); assert (*un_it == 0x65e5); assert (--un_it == utf8::unchecked::iterator<char*>(threechars)); assert (*un_it == 0x10346);
This is an unchecked version of utf8::iterator. It is faster in many cases, but offers
no validity or range checks.
The library was designed to be:
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:
std::string. 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.
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.