From:	CRDGW2::CRDGW2::MRGATE::"SMTP::CRVAX.SRI.COM::RELAY-INFO-VAX" 23-MAY-1989 02:31
To:	MRGATE::"ARISIA::EVERHART"
Subj:	VMS record formats and VAXC

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Date: 22 May 89 18:58:11 GMT
From: gjc@bu-cs.bu.edu  (George J. Carrette)
Organization: Boston U. Comp. Sci.
Subject: VMS record formats and VAXC
Message-Id: <31586@bu-cs.BU.EDU>
References: <685@marob.MASA.COM>
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A straight fopen(x,"wb") is a pretty darn good approximation to unix
fopen(x,"w"). However, many programs written before the stream_* format was
available in RMS would use a straight "unstructured" 512 byte fixed
record file with no record attributes.

When I write a "binary" "data-file" from VAXC I prefer to use the following:

 fopen(name,"wb","mrs=512","rfm=fix","ctx=rec");

Then, if you want extra speed, use macro versions of getc and putc!

(Note: This getc will return extra characters at the end of some kinds
 of RMS files.)

First fix iobuf in stdio.h to have unsigned char for _ptr and _base
instead of char. Then:

#define xgetc(p) (--(*p)->_cnt>=0?((int)*(*p)->_ptr++):xfilbuf(p))

#define xputc(x,p) \
 (--(*p)->_cnt>=0?(int)(*(*p)->_ptr++=(unsigned char)(x)): \
 xflsbuf((unsigned char)(x),p))

Now xfilbuf and xflsbuf both work by setting (*p)->_cnt = 0
and then calling fgetc and fputc.

The speed-up when using these macro getc and putc over using the DIGITAL 
implementations, which turn into fgetc and fputc, is VERY LARGE indeed.

Q: Has DIGITAL made any improvements here in the latest releases of
   the VAXC compiler? I'm still using V2.3 myself.
Q: Can anyone figure out why a "FILE *" in VAXC is a pointer to a pointer to
   an iobuf, instead of just being a pointer to an iobuf? What is
   gained by having an extra level of indirection?

-gjc