How to resolve incorrect fortran read from data text file?

Question

I have a text file with two numbers on the same line

108  6.7522

I have a fortran subroutine READCN that stores the numbers 108 6.7522 from the text file into the variables NN and BOX

    SUBROUTINE READCN ( CNFILE, BOX )
    CHARACTER   CNFILE*(*)
    REAL        BOX
    INTEGER     CNUNIT
    PARAMETER ( CNUNIT = 10 )
    INTEGER     NN
    OPEN ( UNIT = CNUNIT, FILE = CNFILE, STATUS = 'OLD',
 :         FORM = 'UNFORMATTED'                        )

    READ ( CNUNIT ) NN, BOX
    WRITE(*,*) NN, BOX
    CLOSE ( UNIT = CNUNIT )
    RETURN
    END

The output for READCN variables NN BOX is

   3.2997999      2.74554597E-31

How do I read the values correctly?

This program is taken from http://www.ccl.net/cca/software/SOURCES/FORTRAN/allen-tildesley-book/f.12

When I attempted to remove the format option in the read command this was the follow error I received

At line 686 of file MCNPT.f (unit = 10, file = 'LATTICE-256.txt')
Fortran runtime error: Missing format for FORMATTED data transfer

By "remove the format option in the read command" you mean "remove the form='unformatted' in the open statement"? — francescalus

francescalus francescalus · Accepted Answer · 2014-05-17T15:36:32

Moving from using unformatted input to formatted input requires three actions:

changing the input to a "text file";
opening the file for formatted, rather than unformatted, I/O;
providing a format for the read statements.

You've done the first two of these. [If you didn't know, removing form='unformatted' means that the default of formatted I/O is used.]

All that remains is to use a format specifier in the subsequent reads. This is where the compiler is complaining.

The simplest formatted read to use is list-directed, which is given by fmt=* specifier in the read. This should be sufficient for your case, but you should ensure you are happy with its limitations.

To be precise: replace

      OPEN ( UNIT = CNUNIT, FILE = CNFILE, STATUS = 'OLD',
     :         FORM = 'UNFORMATTED'                        )
      READ ( CNUNIT ) NN, BOX

with

      OPEN ( UNIT = CNUNIT, FILE = CNFILE, STATUS = 'OLD')
      READ ( CNUNIT, * ) NN, BOX

How to resolve incorrect fortran read from data text file?

1 Answers