How can I write a to_upper() or to_lower() function in F90?

Question

How does one write a (Intel) F90 function that converts a string into lowercase (or, alternatively, uppercase)? I want to pass a character array to the function and have it retu

Answer 1

Here's one that doesn't rely on the ASCII representation

Pure Function to_upper (str) Result (string)

!   ==============================
!   Changes a string to upper case
!   ==============================

    Implicit None
    Character(*), Intent(In) :: str
    Character(LEN(str))      :: string

    Integer :: ic, i

    Character(26), Parameter :: cap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
    Character(26), Parameter :: low = 'abcdefghijklmnopqrstuvwxyz'

!   Capitalize each letter if it is lowecase
    string = str
    do i = 1, LEN_TRIM(str)
        ic = INDEX(low, str(i:i))
        if (ic > 0) string(i:i) = cap(ic:ic)
    end do

End Function to_upper

You can easily change this to to_lower by switching the low and cap strings in the loop.