Convert integers to strings to create output filenames at run time

Question

I have a program in Fortran that saves the results to a file. At the moment I open the file using

OPEN (1, FILE = \'Output.TXT\')

However,

Answer 1

A much easier solution IMHO ...................

character(len=8) :: fmt ! format descriptor

fmt = '(I5.5)' ! an integer of width 5 with zeros at the left

i1= 59

write (x1,fmt) i1 ! converting integer to string using a 'internal file'

filename='output'//trim(x1)//'.dat'

! ====> filename: output00059.dat

Answer 2

To convert an integer to a string:

integer :: i    
character* :: s    
if (i.LE.9) then
     s=char(48+i)    
else if (i.GE.10) then
     s=char(48+(i/10))// char(48-10*(i/10)+i)    
endif

Answer 3

I've tried @Alejandro and @user2361779 already but it gives me an unsatisfied result such as file 1.txt or file1 .txt instead of file1.txt. However i find the better solution:

...
integer :: i
character(len=5) :: char_i     ! use your maximum expected len
character(len=32) :: filename

write(char_i, '(I5)') i        ! convert integer to char
write(filename, '("path/to/file/", A, ".dat")') trim(adjustl(char_i))
...

Explanation:

e.g. set i = 10 and write(char_i, '(I5)') i

char_i                gives  "   10" ! this is original value of char_i

adjustl(char_i)       gives  "10   " ! adjust char_i to the left

trim(adjustl(char_i)) gives  "10"    ! adjust char_i to the left then remove blank space on the right

I think this is a simplest solution that give you a dynamical length filename without any legacy blank spaces from integer to string conversion process.

Answer 4

For a shorten version. If all the indices are smaller than 10, then use the following:

do i=0,9
   fid=100+i
   fname='OUTPUT'//NCHAR(i+48) //'.txt'
   open(fid, file=fname)
   !....
end do

For a general version:

character(len=5) :: charI
do i = 0,100
   fid = 100 + i
   write(charI,"(A)"), i
   fname ='OUTPUT' // trim(charI) // '.txt'
   open(fid, file=fname)
end do

That's all.

Answer 5

Well here is a simple function which will return the left justified string version of an integer:

character(len=20) function str(k)
!   "Convert an integer to string."
    integer, intent(in) :: k
    write (str, *) k
    str = adjustl(str)
end function str

And here is a test code:

program x
integer :: i
do i=1, 100
    open(11, file='Output'//trim(str(i))//'.txt')
    write (11, *) i
    close (11)
end do
end program x

Answer 6

Here is my subroutine approach to this problem. it transforms an integer in the range 0 : 9999 as a character. For example, the INTEGER 123 is transformed into the character 0123. hope it helps.

P.S. - sorry for the comments; they make sense in Romanian :P

 subroutine nume_fisier (i,filename_tot)

   implicit none
   integer :: i

   integer :: integer_zeci,rest_zeci,integer_sute,rest_sute,integer_mii,rest_mii
   character(1) :: filename1,filename2,filename3,filename4
   character(4) :: filename_tot

! Subrutina ce transforma un INTEGER de la 0 la 9999 in o serie de CARACTERE cu acelasi numar

! pentru a fi folosite in numerotarea si denumirea fisierelor de rezultate.

 if(i<=9) then

  filename1=char(48+0)
  filename2=char(48+0)
  filename3=char(48+0)
  filename4=char(48+i)  

 elseif(i>=10.and.i<=99) then

  integer_zeci=int(i/10)
  rest_zeci=mod(i,10)
  filename1=char(48+0)
  filename2=char(48+0)
  filename3=char(48+integer_zeci)
  filename4=char(48+rest_zeci)

 elseif(i>=100.and.i<=999) then

  integer_sute=int(i/100)
  rest_sute=mod(i,100)
  integer_zeci=int(rest_sute/10)
  rest_zeci=mod(rest_sute,10)
  filename1=char(48+0)
  filename2=char(48+integer_sute)
  filename3=char(48+integer_zeci)
  filename4=char(48+rest_zeci)

 elseif(i>=1000.and.i<=9999) then

  integer_mii=int(i/1000)
  rest_mii=mod(i,1000)
  integer_sute=int(rest_mii/100)
  rest_sute=mod(rest_mii,100)
  integer_zeci=int(rest_sute/10)
  rest_zeci=mod(rest_sute,10)
  filename1=char(48+integer_mii)
  filename2=char(48+integer_sute)
  filename3=char(48+integer_zeci) 
  filename4=char(48+rest_zeci)

 endif

 filename_tot=''//filename1//''//filename2//''//filename3//''//filename4//''
 return
 end subroutine nume_fisier