Testing for a lead-byte value

Table 15. Lead byte and trail byte values
Code page	Language or standard	Lead-byte values	Trail-byte values
BIG-5	Traditional Chinese	161 through 254	64 through 126161 through 254
CP949	Korean	129 through 254	65 through 9097 through 122129 through 254
CP950	Traditional Chinese	129 through 254	64 through 126128 through 254
CP936	Simplified Chinese	129 through 254	64 through 126128 through 254
CP1361	Korean	132 through 211216 through 222224 through 249	65 through 127129 through 254
EUCJIS	Japanese	142164 through 254	161 through 254
GB2312	Simplified Chinese	161 through 254	161 through 254
GB18030¹	Extended Chinese	-	-
KSC5601	Korean	161 through 254	161 through 254
SHIFT-JIS	Japanese	129 through 159224 through 252	64 through 126128 through 252
UTF-8	Unicode	193 through 239	128 through 191

¹ The GB18030 code page is a multi-byte code page, consisting of one-, two-, and four-byte characters, that extends the GB2312 code page and includes all characters defined in Unicode. Unlike most multi-byte code pages that OpenEdge supports, you cannot use the lead byte of multi-byte characters in the GB18030 code page to determine the character's length. OpenEdge uses the International Components for Unicode (ICU) library to convert characters between the GB18030 code page and Unicode within the OpenEdge GUI client.

You cannot always assume a byte with a lead-byte value is a lead byte, or a byte with a trail-byte value is a trail byte. This is because the possible values for trail bytes overlap those of lead bytes and single bytes. For example, the value 164 can correspond to a lead byte or a trail byte. To determine which it is, you must inspect the string.

To determine if a byte has a lead-byte value, use the IS-LEAD-BYTE function, which evaluates a character expression and returns YES if the first byte of the first character of the character string has a value within the range permitted for lead bytes. Otherwise, IS-LEAD-BYTE returns NO. IS-LEAD-BYTE has the following syntax:

IS-LEAD-BYTE ( string )

In the following example, IS-LEAD-BYTE examines a string whose first character is single byte. Since the first byte of the first character of the string is not a lead byte, its value is not within the range permitted for lead bytes, IS-LEAD-BYTE returns NO, and the example displays Lead: no:

DEFINE VARIABLE lLead AS LOGICAL NO-UNDO.

lLead = IS-LEAD-BYTE("xy

").

DISPLAY lLead WITH 1 COLUMN.

The following example is identical to the preceding example except that the first character of the string is double byte. Since the first byte of the first character of the string is a lead byte, its value falls within the range permitted for lead bytes, IS-LEAD-BYTE returns YES, and the example displays Lead: yes: