It does not, however, specify whether letters precede digits or
follow them. As a result, if strings of mixed text are sorted using
relational operators the results may be machine dependent. For
example, the expression
'APPLE' .LT. 'APRICOT'
is always true because at the two strings first differ at the third character position, and the letter 'P' precedes 'R' in all Fortran collating sequences. However:
'A1' .GT. 'AONE'
will have a value true if your system uses EBCDIC but false if it uses ASCII, because the digits follow letters in the former and precede them in the latter.
In order to allow character comparisons to be made in a truly portable way, Fortran has provided four additional intrinsic functions. These perform character comparisons using the ASCII collating sequence no matter what the native character code of the machine. These functions are:
|LGE(S1, S2)||greater than or equal to|
|LGT(S1, S2)||greater than|
|LLE(S1, S2)||less than or equal to|
|LLT(S1, S2)||less than.|
They take two character arguments (of any length) and return a
logical value. Thus the expression:
will always have the value false.
Character comparisons are case-sensitive on machines which have lower-case letters in their character set. It is advisable to convert both arguments to the same case beforehand.