Fortran and Octave/Matlab: Variable File Names

Suppose you want to write to files with names that are not known before compile time, or loop over a set of related filenames. For example, you may want to write to files file0001.txt, file0002.txt, ... so on.

Doing this in Octave/Matlab is quite easy: For example:

	filename = sprintf('file%04d.txt',i) % say i = 10
	f1 = fopen(filename, 'w')
	% write stuff to the file, ex: fprintf(f1,"%d",25)
	fclose(f1)

view raw fooWrite.m hosted with ❤ by GitHub

In Fortran 90, you do something similar

	program foo
	character(len=12) :: filename
	integer :: i
	i = 10
	write (filename, "(A4,i0.4,A4)") "file", i,".dat"
	print*, trim(filename)
	open(1, file=filename)
	! write to the file
	close(1)
	end program foo

view raw fooName.f90 hosted with ❤ by GitHub

It is easy to extend this idea to create files using loops.