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, I now want to run a loop, and save the results of each iteration to the files 'Output1.TXT', 'Output2.TXT', 'Output3.TXT', and so on.
Is there an easy way in Fortran to constuct filenames from the loop counter i?
you can write to a unit, but you can also write to a string
program foo character(len=1024) :: filename write (filename, "(A5,I2)") "hello", 10 print *, trim(filename) end program Please note (this is the second trick I was talking about) that you can also build a format string programmatically.
program foo character(len=1024) :: filename character(len=1024) :: format_string integer :: i do i=1, 10 if (i 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 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 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.
I already showed this elsewhere on SO (How to use a variable in the format specifier statement? , not an exact duplicate IMHO), but I think it is worthwhile to place it here. It is possible to use the techniques from other answers for this question to make a simple function
function itoa(i) result(res) character(:),allocatable :: res integer,intent(in) :: i character(range(i)+2) :: tmp write(tmp,'(i0)') i res = trim(tmp) end function which you can use after without worrying about trimming and left-adjusting and without writing to a temporary variable:
OPEN(1, FILE = 'Output'//itoa(i)//'.TXT') It requires Fortran 2003 because of the allocatable string.
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.
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 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=10.and.i=100.and.i=1000.and.i