Apparently not able to append a string to another

Question

I have a very simple problem, that I am yet to find an answer to.

Is there any way in which I can append a character (in particular, a white space) to a character that has already been initialized in Fortran?

Apparently

CHARACTER(2000) :: result
result = ''
result = result // ' '

does not work.

Answer 1

Be aware that all strings are filled with trailing blanks (space characters) after their last non-space character. This is very important!

'a' // ' ' really produces  'a '

but

result = result // ' '

produces a 2001 character string (you are appending to the whole 2000-character result including the trailing blanks), which is then truncated on assignment, so that result ends up being the same.

You may want

result = trim(result) // ' '

but it is also useless, because the string is filled with trailing blanks (spaces) anyway.

It would make sense when you append something non-blank:

  character(4) :: str

  str = "a"
  str = trim(str) // "bcd"
  print *, str
end

It should print abcd.

---

If you want to make the variable larger, you have to use:

character(:), allocatable:: result
result = 'a'  !now contains 'a' and has length 1
result = result // 'b' !now contains 'ab' and has length 2

It works also with space characters:

character(:), allocatable:: result
result = ' '  !now contains ' ' and has length 1
result = result // ' ' !now contains '  ' and has length 2

(In old versions of Intel Fortran one had to enable reallocation on assignment for this behaviour.)