How to check if character is upper or lowercase in Fortran?-CodePudding

Within Fortran, what are the library functions, if any (I'm using gfortran 11) that return whether the character is upper or lower case?

character :: c
c = 'l'
print *, is_lower(c) ! should display 'T'
print *, is_upper(c) ! should display 'F'
c = 'L'
print *, is_upper(c) ! should display 'T'

What should I be using in place of is_lower and is_upper? I can try to roll my own, but the comparison operators are weird enough with characters that I can't be sure of exactly what I'm doing.

CodePudding user response：

You could use an ascii comparison... trasform c with iachar in integer and compare it with the boundaries of uppercase characters (from 65 to 90) or with the boundaries of lowercase characters (from 97 to 122) that is limited solution because it will not take care of strange characters that are uppercase or lowercase like ÈÉ

CodePudding user response：

Thanks to @Gicu Aftene's help, I have this hacky way of doing the checking for each character:

module char_cases
  implicit none

  private
  public :: is_upper_ascii, is_lower_ascii

  character(len=26), parameter :: uca = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
  character(len=26), parameter :: lca = 'abcdefghijklmnopqrstuvwxyz'

contains

  pure elemental logical function is_upper_ascii(ch)
    character, intent(in) :: ch
    is_upper_ascii = index(uca, ch) /= 0
  end function is_upper_ascii

  pure elemental logical function is_lower_ascii(ch)
    character, intent(in) :: ch
    is_lower_ascii = index(lca, ch) /= 0
  end function is_lower_ascii

end module char_cases