MBLead (W*S)

Module

USE IFNLS

result = MBLead (char)

Results

The result type is LOGICAL(4). The result is .TRUE. if char is the first character of a multibyte character sequence; otherwise, .FALSE..

MBLead only works stepping forward through a whole multibyte character string. For example:

       DO i = 1, LEN(str)  ! LEN returns the number of bytes, not the
                           !  number of characters in str
          WRITE(*, 100) MBLead (str(i:i))
       END DO
 100   FORMAT (L2, \)

MBLead is passed only one character at a time and must start on a lead byte and step through a string to establish context for the character. MBLead does not correctly identify a nonlead byte if it is passed only the second byte of a multibyte character because the status of lead byte or trail byte depends on context.

The function MBStrLead is passed a whole string and can identify any byte within the string as a lead or trail byte because it performs a context-sensitive test, scanning all the way back to the beginning of a string if necessary to establish context. So, MBStrLead can be much slower than MBLead (up to n times slower, where n is the length of the string).