How to get code point number for a given character in a utf-8 string?

Question

I want to get the UCS-2 code points for a given UTF-8 string. For example the word "hello" should become something like "0068 0065 006C 006C 006F". Please note that the characters could be from any language including complex scripts like the east asian languages.

So, the problem comes down to "convert a given character to its UCS-2 code point"

But how? Please, any kind of help will be very very much appreciated since I am in a great hurry.

Thanks in advance

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Transcription of questioner's response posted as an answer

Thanks for your reply, but it needs to be done in PHP v 4 or 5 but not 6.

The string will be a user input, from a form field.

I want to implement a PHP version of utf8to16 or utf8decode like

function get_ucs2_codepoint($char)
{
    // calculation of ucs2 codepoint value and assign it to $hex_codepoint
    return $hex_codepoint;
}

Can you help me with PHP or can it be done with PHP with version mentioned above?

Thank you again.

Answer 1

Use an existing utility such as iconv, or whatever libraries come with the language you're using.

If you insist on rolling your own solution, read up on the UTF-8 format. Basically, each code point is stored as 1-4 bytes, depending on the value of the code point. The ranges are as follows:

• U+0000 — U+007F: 1 byte: 0xxxxxxx
• U+0080 — U+07FF: 2 bytes: 110xxxxx 10xxxxxx
• U+0800 — U+FFFF: 3 bytes: 1110xxxx 10xxxxxx 10xxxxxx
• U+10000 — U+10FFFF: 4 bytes: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

Where each x is a data bit. Thus, you can tell how many bytes compose each code point by looking at the first byte: if it begins with a 0, it's a 1-byte character. If it begins with 110, it's a 2-byte character. If it begins with 1110, it's a 3-byte character. If it begins with 11110, it's a 4-byte character. If it begins with 10, it's a non-initial byte of a multibyte character. If it begins with 11111, it's an invalid character.

Once you figure out how many bytes are in the character, it's just a matter if bit twiddling. Also note that UCS-2 cannot represent characters above U+FFFF.

Since you didn't specify a language, here's some sample C code (error checking omitted):

wchar_t utf8_char_to_ucs2(const unsigned char *utf8)
{
  if(!(utf8[0] & 0x80))      // 0xxxxxxx
    return (wchar_t)utf8[0];
  else if((utf8[0] & 0xE0) == 0xC0)  // 110xxxxx
    return (wchar_t)(((utf8[0] & 0x1F) << 6) | (utf8[1] & 0x3F));
  else if((utf8[0] & 0xF0) == 0xE0)  // 1110xxxx
    return (wchar_t)(((utf8[0] & 0x0F) << 12) | ((utf8[1] & 0x3F) << 6) | (utf8[2] & 0x3F));
  else
    return ERROR;  // uh-oh, UCS-2 can't handle code points this high
}

Answer 2

If you are using C, then try mbstowcs function. This should be able to convert utf8 to ucs2.

http://www.opengroup.org/onlinepubs/009695399/functions/mbstowcs.html

Answer 3

I'm amused because I just gave this problem to students on a final exam. Here's a sketch of UTF-8:

hex         binary                   UTF-8 binary
0000-007F   00000000 0abcdefg   =>   0abcdefg
0080-07FF   00000abc defghijk   =>   110abcde 10fghijk
0800-FFFF   abcdefgh ijklmnop   =>   1110abcd 10efghij 10klmnop

And here's some C99 code:

static void check(char c) {
  if ((c & 0xc0) != 0xc0) RAISE(Bad_UTF8);
}

uint16_t Utf8_decode(char **p) { // return code point and advance *p
  char *s = *p;
  if ((s[0] & 0x80) == 0) {
    (*p)++;
    return s[0];
  } else if ((s[0] & 0x40) == 0) {
    RAISE (Bad_UTF8);
    return ~0; // prevent compiler warning
  } else if ((s[0] & 0x20) == 0) {
    if ((s[0] & 0xf0) != 0xe0) RAISE (Bad_UTF8);
    check(s[1]); check(s[2]);
    (*p) += 3;
    return ((s[0] & 0x0f) << 12)
         + ((s[1] & 0x3f) <<  6)
         + ((s[2] & 0x3f));
  } else {
    check(s[1]);
    (*p) += 2;
    return ((s[0] & 0x1f) << 6)
         + ((s[1] & 0x3f));
  }
}

Answer 4

Thanks for your reply, but it needs to be done in PHP v 4 or 5 but not 6.

The string will be an user input, from a form field.

i want to implement a PHP version of utf8to16 or utf8decode like

function get_ucs2_codepoint($char)
{
    // calculation of ucs2 codepoint value and assign it to $hex_codepoint

    return $hex_codepoint;
}

can you help me with PHP or can it be done with PHP with version mentioned above?

Thank you again.

Answer 5

Scott Reynen wrote a function to convert UTF-8 into Unicode. I found it looking at the PHP documentation.

function utf8_to_unicode( $str ) {

    $unicode = array();        
    $values = array();
    $lookingFor = 1;

    for ($i = 0; $i < strlen( $str ); $i++ ) {
        $thisValue = ord( $str[ $i ] );
    if ( $thisValue < ord('A') ) {
        // exclude 0-9
        if ($thisValue >= ord('0') && $thisValue <= ord('9')) {
             // number
             $unicode[] = chr($thisValue);
        }
        else {
             $unicode[] = '%'.dechex($thisValue);
        }
    } else {
          if ( $thisValue < 128) 
        $unicode[] = $str[ $i ];
          else {
                if ( count( $values ) == 0 ) $lookingFor = ( $thisValue < 224 ) ? 2 : 3;                
                $values[] = $thisValue;                
                if ( count( $values ) == $lookingFor ) {
                    $number = ( $lookingFor == 3 ) ?
                        ( ( $values[0] % 16 ) * 4096 ) + ( ( $values[1] % 64 ) * 64 ) + ( $values[2] % 64 ):
                        ( ( $values[0] % 32 ) * 64 ) + ( $values[1] % 64 );
            $number = dechex($number);
            $unicode[] = (strlen($number)==3)?"%u0".$number:"%u".$number;
                    $values = array();
                    $lookingFor = 1;
          } // if
        } // if
    }
    } // for
    return implode("",$unicode);

} // utf8_to_unicode

Answer 6

PHP's unicode_decode may be what you're looking for:

unicode_decode($my_utf8_string, 'utf8');