defining path for file in FORTRAN

Question

In bash I could write a simple script like below; to read the content of a file in the folder as I define the path for the file using environment variable "fileplace"

#!/bin/bash

fileplace="/home/vijay/data1/process-folder1/"

cat $file/file1.dat

I would like to achieve the same like above in FORTRAN 90, by defining the path using variable. I want to do like this because my folder location path is long and I wanted to avoid using & and + symbol for long lines in FORTRAN 90.

I have tried writing simple FORTRAN 90 code as below for testing.

program test_read
implicit none

open (unit=10, status="old",file="/home/vijay/data1/process-folder1/file1.dat")
read(10,*) junk
write(*,*) junk 

stop
end

If can I want to avoid using the long path (/home/vijay/data1/process-folder1/) in the FORTRAN code. Is there any possibility to achieve this? If yes can anyone help to correct this FORTRAN code? Appreciate any help in advance.

Thank you

Vijay

Shack

Answer 1

Fortran isn't a good language to work with strings, but this is still possible.

You need a variable, where you can store the path. If this path is a constant and already known at compile time, you can simply write

CHARACTER(*), PARAMETER :: fileplace = "/home/vijay/data1/process-folder1/"

The file can then be opened with

OPEN(unit=10, status="old",file=fileplace//"file1.dat")

If you want to change the path during execution time, you have to set a appropriate length for fileplace and adjust it accordingly, when you want to use it:

CHARACTER(100) :: fileplace

WRITE(fileplace,*) "/home/vijay/data1/process-folder1/"
OPEN(unit=10, status="old", file=TRIM(ADJUSTL(fileplace))//"file1.dat")

The functions ADJUSTL() and TRIM() move the content of string to the left to remove any leading whitespace and then cut all trailing whitespace.

Freudberg

My path is like this (/home/vijay/Simulation-Folder-Feb2013/chapter6-lyo-paper1-Vj/TRAJ-malto12per/). I used in preamble (CHARACTER() :: fileplace="/home/vijay/Simulation-Folder-Feb2013/chapter6-lyo-paper1-Vj/TRAJ-malto12per/"). Then in the body of the code i typed (OPEN(unit=31, status="old",file=fileplace//"maltoLyo12per-reimage-set1.traj"). But I get error like this [CHARACTER() :: fileplace="/home/vijay/Simulation-Folder-Feb2013/chapter6-lyo- 1 Error: Entity with assumed character length at (1) must be a dummy argument or a PARAMETER]. Could you give any comment on this? Thanks – Shack

Sry... I forgot the PARAMETER. – Freudberg

The use of a list directed internal write to define a character variable with the value of a character literal constant is unnecessarily convoluted. A simple assignment statement would be better (that would also allow the reference to ADJUSTL to be removed). – Interconnect

Answer 2

You can use some Fortran like this:

fileplace = "/home/vijay/data1/process-folder1/"

open (unit=10, status="old",file=fileplace//"file1.dat")

Note:

1. In Fortran string concatenation is expressed by the operator //.

2. You'll have to declare the character variable fileplace, something like

   character(len=:), allocatable :: fileplace

ought to do it.

Fortran 2003 introduced the standard procedure GET_ENVIRONMENT_VARIABLE which may also be of interest to you if your compiler implements it.

Sandstrom