Can Fortran Incorporate Variables in Output File Names?

[angura]

Hi,

I looked around in some forums, but couldn't find a good answer to this problem: my programmes produce several output files. When the programm is finished, I add certain simulation parameters to the file name, so that I see later, to which simulation run this file belongs.
(for example, a file "result.dat" is renamed to "result_500.dat" because the 500 is a certain parameter in that programm).

Now i don't want to manually rename a lot of files, but instead I'm looking for a way to make Fortran incorporate certain variables in the file names.
I only know this way of declaration:

open(unit=1,status='unknown',file='result.dat')

Assuming I have a certain variable (e.g. an integer called "number")
Is it possible to assign a file name "result_*number*.dat", so that I only have to change the value of "number" and all files have that in their names?

Thanks for your help.

 

[Useful nucleus]

A possible solution , say you have 10 files with differnet names and you want to add the number 19 to all of them . Put the initial names(i.e., before adding 19) of these files in a character array defined as follow:
CHARACTER(len=25),DIMENSION(10)::filenames

also, define a character that contains the number(19)
CHARACTER(len=2)::number
number='19' !The quotqtion are important

then to add the number to the names use the concatenation operator as follows:
DO i=1,10
filename(i)=filaename(i) // number// '.dat'
END DO

now you have the names ready in the array, you can open ten files now with the statement:
DO i=1,10
OPEN(UNIT=i+10,FILE=filename(i),STATUS='replace',ACTION='write')
END DO


Now you have ten files with the required names ready to write in them.


May be this is not the best way, but I hope it works for you.

 

[angura]

Thanks for your answer! That's exactly what I'm looking for.
I'm still having a little trouble though, because the numbers that should be in the filenames are integer values and I don't know how to convert them into characters.
It's supposed to work with the simple write - command, but somehow I can't get it to work correctly :(

 

[Useful nucleus]

Hi angura,

You can use an internal file to do this. Say we have an integer i=567, and a character called number and we want to assign the value of i to the character then this piece of code will do the job:
...
INTEGER::i
CHARACTER(len=10)::number
i=567
WRITE(number,100) i
100 FORMAT(I3)
...


A couple of comments, check that the length of the character is enough since this can create a runtime error. Also note that the write statement above creates a buffer file and do the conversion .

 

[mathmate]

Take care that the number has three digits when you use format I3.
If you want numbers with a maximum of three digits, with leading zeroes for those below 100, you can use the Iw.m conversion, for example,

WRITE(number,100) i 
100 FORMAT(I3.3)

will produce 007 when i=7.
This is important because you do not want a file name like:
ACE 7.dat
but rather
ACE007.dat

 

[melody33]

I also have the same problem.

However, the answer doesn't work to me.
I used gfortran to compile, then it said filename must be scalar.
How can I fix this? or should I use another compiler?

 

[angura]

At which position does it complain, that filename should be scalar?
Could you post a minimal example of your code?

 

[minger]

I typically write to a variable, using variable and strings, which I then open. Here is an example from a subroutine I have:

DO m=1,nFiles

  WRITE(fname,'(a,i4.4,a)')'grid',m,'.fast'
  OPEN(12,file=fname,form='formatted')
...
...
END DO

In this particular routine, I open this file which I already have, and modify it, writing out a formatted or post processed file. I concactanate the filenames easily as:

  oname = 'post.'//fname
  WRITE(6,*) 'OPENING:  ',oname
  OPEN(13,file=oname,file='formatted')

I 'used' to open several files and then write or open the file unit number as the do loop iterator, i.e.

DO i=1,10
  OPEN(i,file='whatever')
END DO

But the flexibility of the way I'm doing it up there will save you a lot of hassle down the road. I recommend it.