I have opened a file to write a number. I have to write the number at the end of the file so
how to go to the last line to write on it?
You should open the file with
open(..., position="append",...)
Alternatively, you can inquire for the size of the file
inquire(...,size=some_integer_variable,...)
then if the file is a direct access file, you can use this size to calculate the record number of the final record. Alternatively, if the access mode is "stream", you can use
write(..., pos=some_integer_variable)
to write starting at the end of the file.
I've been using the same trick for years, and would be interested in a more elegant way but I can propose you the following method. Note that it is less and less efficient as the file increases in number of lines. Note also that this part of code could endup in an elegant module dedicated to playing with input/output.
Open your file
open(11, file='monfichier')
Compute how many lines there are in your file
nbline = 0 ! should have been declared as an integer
do while(.true.)
read(11,*,iostat=ios) ! ios should have been declared as an integer
if( ios > 0 ) then
stop 'problem somewhere'
else if( ios < 0 ) then ! end of file is reached
exit
else
nbline = nbline + 1
end if
end do
close(11)
at this step, you have the total number of lines stored in variable nbline.
If you want to print something at the Nth line before the last line, then
open(11, file='monfichier')
do i = 1, nbline - N ! see my nota bene at the end of my answer; i and N are integers
read(11,*)
end do
write(11,*)'hello world'
Et voilà !
N.B. : Please be carefull in the way you count for nbline-N or nbline-(N-1), depending on exactly what you want.
subroutine to_last_rec (luout)
! purpose: position to last record of file
implicit none
integer :: luout
logical :: ende
! first executable statement
ende = .FALSE.
do while ( .NOT. ende)
read (luout,*,end=100)
enddo
100 return
end subroutine to_last_rec
PROGRAM example
IMPLICIT NONE
INTEGER :: ierr
OPEN(UNIT=13,FILE="ex.dat")
CALL FSEEK(13, 0, 2, ierr)
! DO WHATEVER YOU WANT THEN
CLOSE(13)
END PROGRAM example
the call to fseek goes to the end of the file ( used like that, check the usage http://docs.oracle.com/cd/E19957-01/805-4942/6j4m3r8ti/index.html)
Related
I would like to read the same line of a file many time in Fortran. The concerned data are real values. I tried to build this code as test but I am always getting it wrong.
program advance
implicit none
integer , parameter :: ut = 20
character(len=7) :: fname = 'dat.dat'
integer :: n, idx
character(len=100) :: lnumber
open(unit = ut, file =fname, status='old', action='read')
n = 10
do idx = 1, n
read(ut, '(a)', advance = 'no') lnumber
print *, lnumber
end do
end program advance
The dat.dat file contains one line with 25.325654515464564564
The code return the following error.
At line 13 of file advance.f90 (unit = 20, file = 'dat.dat')
Fortran runtime error: End of record
How do I fix this bug?
Such non-advancing input (using advance='no') doesn't mean that the file position is not advanced at all. It means that the file position isn't advanced beyond what is needed to satisfy the requirements of the input list.
So, in this case, the file position is advanced by reading the single "real number" into the character variable lnumber. The next read will continue from this later point. This later point happens to be the end of the file.
With advancing input more generally, the file position is advanced to the start of the next record even if the record is not required in entirety.
As High Performance Mark comments, reading the same line over and over again likely isn't what you should be doing. You could read the line into a character variable (such as is done here) and repeatedly use that variable as an internal file. However, if you really want to read a line again, consider backspace.
I create a fortran code to calculate the temperature of a cfd model. This code will be called on every iteration of a steady state simulation and calculate the temperature. On every calling of my code/iteration i want my fortran code also save the temperature field on a txt file and save. After calculating the temperature field and saving the values in TFIELD(100;1:6) the part with saving in txt file looks like:
OPEN(UNIT=35,FILE='W:\temperaturField.txt',
&FORM ='FORMATTED',STATUS='UNKNOWN',
&ACTION='READWRITE')
WRITE (35,FMT='5(F8.3,2X))') TFIELD(100,1:6)
With this code it only overwrites the first line of my txt file on every iteration. But i want to paste every TFIELD(100,1:6) array on a new line. How can i do this?
Add POSTITION='APPEND' to the OPEN:
OPEN(UNIT=35,FILE='W:\temperaturField.txt',
&FORM ='FORMATTED',STATUS='UNKNOWN',POSITION='APPEND',
&ACTION='READWRITE')
It seems like you are opening and closing the file for each iteration. This is a quick and dirty method if you need to debug, but it's slow.
If you want to do that, you might want to do what #Jack said: Include a POSITION='APPEND' to the OPEN statement to set the position to write the data to the end of the file. Also, you need to make sure that you close it every time.
A better (more efficient) method would be to keep the file open for the whole time. I'd do that with a module:
module temp_writer_module
implicit none
integer :: temp_writer_unit
logical :: is_opened = .FALSE.
private :: temp_writer_unit, is_opened
contains
subroutine temp_writer_open()
integer :: ios
character(len=100) :: iomsg
if (is_opened) then
print*, "Warning: Temperature file already openend"
return
end if
open(newunit=temp_writer_unit, file='W:\temperatureField', &
form='FORMATTED', status='UNKNOWN', action='WRITE', &
iostat=ios, iomsg=iomsg)
if (ios /= 0) then
print*, "Error opening temperature file:"
print*, trim(iomsg)
STOP
end if
is_opened = .TRUE.
end subroutine temp_writer_open
subroutine temp_writer_close()
if (.not. is_opened) return
close(temp_writer_unit)
is_opened = .FALSE.
end subroutine temp_writer_close
subroutine temp_writer(temps)
real, intent(in) :: temps(6)
integer :: ios
character(len=100) :: iomsg
if (.not. is_opened) call temp_writer_open()
write(temp_writer_unit, *, iostat=ios, iomsg=iomsg) temps
if (ios /= 0) then
print*, "Error writing to temperature file:"
print*, trim(iomsg)
end if
end subroutine temp_writer
end module temp_writer_module
Then you can use it in your program like this:
subroutine calc_temps(...)
use temp_writer_module
<variable declarations>
<calculations>
call temp_writer(tfield(100, 1:6))
end subroutine calc_temps
Just don't forget to call the temp_writer_close routine before your program ends.
I'm trying to write a time variable from a hydrodynamic model into a netcdf file (unlimited dimension variable). I've attached a simplified code example in Fortran90 that highlights my issue.
The subroutine to write the netcdf file is called multiple times during a simulation depending on a user specified output interval (10 times for this example). I can create the file and add attributes for the first time the subroutine is called.
I can't get the start and count variables correct to write the time variable to the file during the subsequent calls of the subroutine. This is the error, at the writing the model time variable, I receive when trying to compile the code: Error: There is no specific function for the generic 'nf90_put_var'
PROGRAM test_netcdf
IMPLICIT NONE
INTEGER :: N
REAL :: time_step = 2.
! Call efdc_netcdf 10 times
DO N=1,10
CALL efdc_netcdf(N, time_step)
time_step=time_step + 1.
ENDDO
END PROGRAM test_netcdf
************************************
! Create NetCDF file and write variables
SUBROUTINE efdc_netcdf(N, time_step)
USE netcdf
IMPLICIT NONE
LOGICAL,SAVE::FIRST_NETCDF=.FALSE.
CHARACTER (len = *), PARAMETER :: FILE_NAME = "efdc_test.nc"
INTEGER :: ncid, status
INTEGER :: time_dimid
INTEGER :: ts_varid, time_varid
INTEGER :: start(1), count(1)
INTEGER :: deltat
INTEGER :: N
REAL :: time_step
start=(/N/)
count=(/1/)
! Create file and add attributes during first call of efdc_netcdf
IF(.NOT.FIRST_NETCDF)THEN
status=nf90_create(FILE_NAME, NF90_CLOBBER, ncid)
! Define global attributes once
status=nf90_put_att(ncid, NF90_GLOBAL, 'format', 'netCDF-3 64bit offset file')
status=nf90_put_att(ncid, NF90_GLOBAL, 'os', 'Linux')
status=nf90_put_att(ncid, NF90_GLOBAL, 'arch', 'x86_64')
! Define deltat variable
status=nf90_def_var(ncid,'deltat',nf90_int,ts_varid)
! Define model time dimension
status=nf90_def_dim(ncid,'efdc_time',nf90_unlimited,time_dimid)
! Define model time variable
status=nf90_def_var(ncid,'efdc_time',nf90_real,time_dimid,time_varid)
status=nf90_enddef(ncid)
! Put deltat during first call
deltat=7
status=nf90_put_var(ncid, ts_varid, deltat)
FIRST_NETCDF=.TRUE.
ENDIF
! Put model time variable
status=nf90_put_var(ncid, time_varid, time_step, start=start, count=count)
! Close file at end of DO loop
IF(N.EQ.10) THEN
status=nf90_close(ncid)
ENDIF
RETURN
END SUBROUTINE efdc_netcdf
The issue is in the line the compiler flags:
status=nf90_put_var(ncid, time_varid, time_step, start=start, count=count)
You are (correctly) trying to write a scalar variable, time_step, into a specific index (start) along variable time_varid, which is defined on a 1-d, infinite-extent dimension. However, in this case, the optional argument count isn't meaningful; you are writing the scalar, and count can only ever be 1. As a result, the fortran bindings for a nf90_put_var() taking a single scalar for input don't have the optional argument defined for count, and that's why you're getting the "no specific function for the generic' nf90_put_var" error from the compiler. This is all perfectly reasonable, but neither the error message nor the docs are super helpful in figuring out how to solve the problem.
You can fix your code by putting the time_step data into a real, dimension(1) variable, and putting that, instead; but easiest is to just get rid of the count specification, which isn't necessary here anyway:
status=nf90_put_var(ncid, time_varid, time_step, start=start)
I have an existing file written by a Fortran program (formatted) and I would like to add few lines at the beginning of the file. The idea is to do so without making a copy of the original file.
I could add a line at the end of the file with:
open(21,file=myfile.dat,status='old',action='write',
form='formatted',position="append")
write(21,*) "a new line"
but when I tried:
open(21,file=myfile.dat,status='old',action='write',
form='formatted',position="rewind")
write(21,*) "a new line"
it overwrites the whole file.
It might be impossible.
At least, I would be glad to have a confirmation that it is effectively impossible.
Yes, it is impossible. With position= you only set the position for writing. Normally you just delete everything past the current record by a write in a sequential file. You may be able to adjust a record at the beginning in a direct access file, but also not just add something at the beginning. You have to make a copy first.
If you are using un-formatted data and know how many lines to expect, try using the direct access file read/write method. This has the potential to store information for each line in a 'record' which can be accessed later much like an array.
In order to append to the beginning, simply create as many empty records as you will have lines in your 'header' at the beginning of the file then go back and change their values to the actual lines you want them to be later.
Example of Direct Access file io:
CHARACTER (20) NAME
INTEGER I
INQUIRE (IOLENGTH = LEN) NAME
OPEN( 1, FILE = 'LIST', STATUS = 'REPLACE', ACCESS = 'DIRECT', &
RECL = LEN )
DO I = 1, 6
READ*, NAME
WRITE (1, REC = I) NAME ! write to the file
END DO
DO I = 1, 6
READ( 1, REC = I ) NAME ! read them back
PRINT*, NAME
END DO
WRITE (1, REC = 3) 'JOKER' ! change the third record
DO I = 1, 6
READ( 1, REC = I ) NAME ! read them back again
PRINT*, NAME
END DO
CLOSE (1)
END
code source, see section on "Direct Access Files":
http://oregonstate.edu/instruct/ch590/lessons/lesson7.html
It is possible !!! Here is a sample program which could accomplish the task.
! Program to write after the end line of a an existing data file
! Written in fortran 90
! Packed with an example
program write_end
implicit none
integer :: length=0,i
! Uncomment the below loop to check example
! A file.dat is created for EXAMPLE defined to have some 10 number of lines
! 'file.dat may be the file under your concern'.
! open (unit = 100, file = 'file.dat')
! do i = 1,10
! write(100,'(i3,a)')i,'th line'
! end do
! close(100)
! The below loop calculates the number of lines in the file 'file.dat'.
open(unit = 110, file = 'file.dat' )
do
read(110,*,end=10)
length= length + 1
end do
10 close(110)
! The number of lines are stored in length and printed.
write(6,'(a,i3)')'number of lines= ', length
! Loop to reach the end of the file.
open (unit= 120,file = 'file.dat')
do i = 1,length
read(120,*)
end do
! Data is being written at the end of the file...
write(120,*)'Written in the last line,:)'
close(120)
end
I am using FORTRAN to read in data from an ASCII text file. The file contains multiple data values per line but the number of values per line is not constant.
101.5 201.6 21.4 2145.5
45.6 21.2
478.5
...
Normally after a read statement, Fortran would go to the next line. What I want to be able to do is read one data value at a time. If it hits the end of the line, it should just continue reading on the next line. Is this possible?
As pointed out by IRO-bot in their comment to your question, the answer has already been given by M.S.B. Below I have merely provided some code illustrating that answer (as M.S.B.'s post contained none):
program test
character(len=40) :: line
integer :: success, i, indx, prev, beginning
real :: value
open(1,file='test.txt')
do
read(1,'(A)',iostat=success) line
if (success.ne.0) exit
prev = 1
beginning = 1
do i=1,len(line)
! is the current character one out of the desired set? (if you
! have got negative numbers as well, don't forget to add a '-')
indx = index('0123456789.', line(i:i))
! store value when you have reached a blank (or any other
! non-real number character)
if (indx.eq.0 .and. prev.gt.0) then
read(line(beginning:i-1), *) value
print *, value
else if (indx.gt.0 .and. prev.eq.0) then
beginning = i
end if
prev = indx
end do
end do
close(1)
end program test
When running this program using the sample lines you provided the output is
101.5000
201.6000
21.40000
2145.500
45.60000
21.20000
478.5000
I hope you will find this helpful.