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From: jliu@hpuxa.ircc.ohio-state.edu (Joe Liu)
Newsgroups: comp.lang.fortran
Subject: Fortran OPEN and WRITE
Message-ID: <962@nisca.ircc.ohio-state.edu>
Date: 8 Apr 90 00:50:34 GMT
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   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, 
each of my data is normalized to 128 ( 1-128), so it's possible to 
represent it with a BYTE on VAX or INTEGER*1 on a Stellar UNIX machine.
Now I must write the data byte by byte successively, because that's how
another program will look for data.  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, thus
the following will result in a 45 bytes file.  

        OPEN (7, FILE='test.dat', FORM='UNFORMATTED')
        DO 10 I=1,5
  10    WRITE (7) I
        CLOSE (7)

 if I have a 5 bytes array and write the array as one record, I will 
get a 5+8= 13 bytes file on the Unix machine.  

         BYTE N(5)
         DO 10 I=1,5
  10     N(I)=I
         OPEN (7,FILE='test.dat, FORM='UNFORMATTED')
         WRITE (7) N
	 CLOSE (7)

  I can look at the 45 bytes or ( 13 bytes) file byte by byte, and I can 
see the first 4 bytes and the last 4 bytes contain some kind of information.
(the size of that record ? ) while the 5th byte contain the right data.
that is, in the 45 bytes files, the 45 bytes are,    
        0,0,0,1, 1 ,0,0,0,1
	0,0,0,1, 2, 0,0,0,1
	0,0,0,1, 3, 0,0,0,1
	0,0,0,1, 4, 0,0,0,1
 	0,0,0,1, 5, 0,0,0,1

 in the 13 bytes file, they are
      0,0,0,5, 1,2,3,4,5, 0,0,0,5 

Although Fortran has no problem to get the right data back when I read 
them out,   The file is not what I must have,  ie, only 1,2,3,4,5 in it.

  On the VAX machine, the bahavior is similar, only difference is that 
it has a 4 bytes extra for each record writen instead of 8.  If I compile
the above two on the VAX I will get a 25 bytes and a 9 bytes file respectively  
instead the 45 bytes and 13 bytes.

   I did try to play with possible options in the OPEN statements
but did not achieve what I wanted.  As I said the FORTRAN itself has 
no problem to read back the right data.  What's behind this ?  Some 
one told me this will not happen on an IBM machine but I did not get 
the chance to try it on IBM yet.  The same purpose can be very easily
achieved in C. That's what I am doing now, use a C program to pick out
the right bytes from a FORTRAN output and write it into the byte by byte
form, to input this into anthoer  graphics application. It will
be nice if I can slightly modify the FORTRAN program to have the compatible
output for the application.

   There must be a lot FORTRAN experts on this group. Please enlighten 
me.  I have sought help from as close as my next door to as far as DEC
technical assitance.  But I still do not know how.

 Thanks.            

Joe