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$WREVERSE (ObjectScript)

Returns the characters in a string in reverse order, recognizing surrogate pairs.




Argument Description
string A string or expression that evaluates to a string.


$WREVERSE returns the characters in string in reverse order. $WREVERSE is functionally identical to $REVERSE, except that $WREVERSE recognizes surrogate pairs. You can use the $WISWIDE function to determine if a string contains a surrogate pair.

A surrogate pair is a pair of 16-bit InterSystems IRIS character elements that together encode a single Unicode character. Surrogate pairs are used to represent certain ideographs which are used in Chinese, Japanese kanji, and Korean hanja. (Most commonly-used Chinese, kanji, and hanja characters are represented by standard 16-bit Unicode encodings.) Surrogate pairs provide InterSystems IRIS support for the Japanese JIS X0213:2004 (JIS2004) encoding standard and the Chinese GB18030 encoding standard.

A surrogate pair consists of high-order 16-bit character element in the hexadecimal range D800 through DBFF, and a low-order 16-bit character element in the hexadecimal range DC00 through DFFF.

The $WREVERSE function counts a surrogate pair as a single character. The $REVERSE function treats a surrogate pair as two characters. In all other aspects, $WREVERSE and $REVERSE are functionally identical. However, because $REVERSE is generally faster than $WREVERSE, $REVERSE is preferable for all cases where a surrogate pair is not likely to be encountered.

For further details on reversing strings, refer to the $REVERSE function.


The following example shows how $WREVERSE treats a surrogate pair as a single character:

  SET spair=$CHAR($ZHEX("D806"),$ZHEX("DC06"))
  SET str="AB"_spair_"CD"
    WRITE !,"String before reversing:"
    ZZDUMP str
  SET wrev=$WREVERSE(str)
    WRITE !,"$WREVERSE did not reverse surrogate pair:"
    ZZDUMP wrev
  SET rev=$REVERSE(str)
    WRITE !,"$REVERSE reversed surrogate pair:"
    ZZDUMP rev

See Also

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