write formatted UTF-8 text file fortran - fortran

Question

I'm trying to write in from fortran a text file.
I did this short test program but of course it does not work, because it does not create a text file that could be readable :
PROGRAM teste
INTEGER(4) REC2,RECL1
character(20) :: charI, wanted
RECL1=10
DO REC2=1,10
OPEN(1,FILE='teste.txt',ACCESS="direct",RECL=RECL1);
write (charI, "(A5,I4)") "hello", REC2
wanted=trim(charI)
write(1,REC=REC2) wanted
close(1)
END DO
END PROGRAM teste
I read lot of different thing but it's still really unclear how it should be written.
Do I need to convert to string before writing ? if yes why ?

Answer 1

Try this
PROGRAM test
IMPLICIT NONE
INTEGER, PARAMETER :: ascii = selected_char_KIND ("ascii")
INTEGER, PARAMETER :: ucs4 = selected_char_KIND ('ISO_10646')
INTEGER :: ix
CHARACTER(len=5,kind=ucs4) :: greeting = ucs4_"hello"
OPEN(10,FILE='test.txt')
DO ix=1,10
WRITE (10,'(A5,I4)') greeting, ix
END DO
CLOSE(10)
END PROGRAM test
... a commentary ...
PROGRAM test
IMPLICIT NONE
All good Fortran programs include the line implicit none; the reason for this is explained in 101 Qs and As here on Stack Overflow and I won't repeat them here.
INTEGER, PARAMETER :: ascii = selected_char_KIND ("ascii")
INTEGER, PARAMETER :: ucs4 = selected_char_KIND ('ISO_10646')
The latest Fortran standard requires that compilers provide these two kinds of character. I'm honestly not sure if iso_10646 is the same as UTF-8 but if it isn't you're probably out of luck. Here, I'm defining two parameters for identifying the character kinds to use later in the program. For your purposes the first of these parameters is unnecessary but you ought to know about it too.
I suppose your compiler might support other character kinds, read the documentation.
(Aside: technically, there is a third character kind name, default. This is likely to set the character kind to either ascii or iso_10646, most likely the former, but if this is important to you check your compiler's documentation.)
INTEGER :: ix
CHARACTER(len=5,kind=ucs4) :: greeting = ucs4_"hello"
In the second of these lines I've defined a character variable with the text hello and of kind ucs4 (which, as you see above, is a local code for iso_10646). Without the prefix ucs4_ the string hello will be interpreted as being of kind default and then converted to ucs4 when stored into the variable greeting. In this case, where there is a 1:1 mapping between the (representation of) the characters in ascii and in ucs4 the prefix is strictly unnecessary but there will be other cases where it won't be.
OPEN(10,FILE='test.txt')
DO ix=1,10
WRITE (10,'(A5,I4)') greeting, ix
END DO
CLOSE(10)
I've removed all the guff about direct access and writing at particular records in a file. It's all unnecessary for what seems to be your immediate need. So this loop will write greeting (ie the ucs4 string hello) and a row index into the file test.txt 10 times.
END PROGRAM test

Answer 2

In your open statement you are opening a file for unformatted input/output. Because you have specified ACCESS="direct" the default is for unformatted, compared with the default as formatted when connected for sequential access.
To make the file "readable" you need to actively open for formatted access, and provide a format for the writing:
open(1,FILE='teste.txt',ACCESS="direct",RECL=RECL1, FORM='formatted')
...
write(1,fmt=...,REC=REC2) ...