J3/05-108r1

To:      J3
From:    Dan Nagle
Subject: Write CSV files
Date:    2005 Feb 07


Fortran programs can read CSV files via list-directed I/O,
but there's no easy way to write one since the separator
between values is optionally blank or comma (with slash
as a Really Special Case).  Also, there's no guarantee
there will be exactly one separator between each pair of values.
If Fortran programs could easily write CSV files,
the value of using Fortran programs along side spreadsheets etc
would be higher than at present.

Number:

Title: Write CSV files Using LDIO

Submitted By: J3

Status: For Consideration

References: 04-007 10.9

Basic Functionality: Provide a quick and easy way to write files
                     using the CSV (Comma Separated Value) format.

Rationale:  CSV files (a/k/a Comma Separated Value) files are
            used by spreadsheets and "higher level math" programs
            such as Mathematica, MATLAB and Maple.  These programs
            provide easy access to graphics and other mathematically
            oriented amenities.

            List directed input treats the comma as a separator,
            but the separator is optionally blank or comma on output.
            If the separator is blank, one or more blanks may be
            between values.  A way to make the optional separator a comma
            allows an easy way to write CSV files, providing easy
            communications to spreadsheet programs and other higher level
            math programs with built-in graphics, algebraic manipulation,
            and other amenities useful with numeric programs, but absent
            in standard Fortran.

            CSV files are formatted, the simplest format from the user's
            perspective is List Directed.  So modify LDIO to serve CSV.

Estimated Impact: Rather minor, the RTL must already reckon where
                  to place a separator in LDIO output, and must already
                  recognize comma on LDIO input.

Detailed Specification: The idea is to modify list directed output
                        as little as possible to gain connectivity
                        from Fortran programs to desktop applications
                        via CSV format.

                        The proposed solution is:

                        Add a new ACCESS form, ACCESS='CSV' which on output
                        (and has no effect on input)

                        1. Implies ACCESS='STREAM', and

                        2. When list directed, requires that the processor
                           not print the "r*" form of repeated values,
                           and

                        3. When listed directed, disallows blanks as separator
                           (which means comma or semicolon is used as per
                           decimal mode), and

                        4. When listed directed, allows blanks on either side
                           of the separator as at present, and

                        5. When listed directed, disallows new records being
                           created (so one write gives one record),
                           and

                        6. Allows explicit formats to be used as needed.

History: M171 Paper J3/05-108