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From: sjc@key.COM (Steve Correll)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran OPEN and WRITE
Message-ID: <1613@key.COM>
Date: 9 Apr 90 21:49:46 GMT
References: <962@nisca.ircc.ohio-state.edu>
Distribution: na
Organization: Key Computer Labs, Fremont, CA
Lines: 31

In article <962@nisca.ircc.ohio-state.edu>, jliu@hpuxa.ircc.ohio-state.edu (Joe Liu) writes:
>    I have been troubled by maybe a very simple problem, what I 
> want to do is:   to write a collection of data into a binary file...
> Suppose I have 5 data points as
> ( 1,2,3,4,5), the binary file I want must be 5 bytes.  However, it seems
> Fortran on the Unix takes 1+8 bytes to write each one byte data...

The Fortran 77 standard requires that the compiler's runtime system be able to
open a "sequential" access file without any prior knowledge of record lengths,
and then skip forward (using "read" with an empty list of data items) or
backward (using "backspace") over each record. To do this, the compiler must
be able to find out the length of each record.

If the host operating system provides variable-length-record files as a
built-in service of its file system, then the compiler may be able to ask the
operating system about the length of a record, and thereby avoid storing them
in the user-visible portion of the file.

Many systems (Unix, for example) do not provide this service, and therefore the
compiler's runtime system must simulate variable length records by storing the
record lengths inside the file. Even some systems which do provide variable
length records provide them in a form which doesn't exactly meet Fortran's
needs.

If you use "direct" access (as described in the Fortran 77 standard) then you
must specify a record length in the "open" statement, and most compilers will
use that instead of storing the record length in the file itself; this will
solve your problem so long as every record can be the same length, or can be
padded to the same length.
-- 
...{sun,pyramid}!pacbell!key!sjc 				Steve Correll