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  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

User · Answer

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

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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

User · Answer

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

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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

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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  lt  10  then             format string     A5 I1           else             format string     A5 I2           endif          write  filename format string   hello   i         print    trim filename      enddo  end program

User · Answer

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 lt  9  then    filename1 char 48 0    filename2 char 48 0    filename3 char 48 0    filename4 char 48 i      elseif i gt  10 and i lt  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 gt  100 and i lt  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 gt  1000 and i lt  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

User · Answer

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          gt  filename  output00059 dat

User · Answer

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

User · Answer

Try the following                character len 30     filename    length depends on expected names     integer              inuit              do i 1 n         write filename    output  i0   txt     i         open newunit iunit file filename                           close iunit      enddo            Where       means other appropriate code for your purpose

[string] Convert integers to strings to create output filenames at run time

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