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From: STEINBERGER@KL.SRI.COM (Richard Steinberger)
Newsgroups: comp.os.vms
Subject: 2 C questions
Message-ID: <12334342671.18.STEINBERGER@KL.SRI.Com>
Date: Sun, 13-Sep-87 14:47:54 EDT
Article-I.D.: KL.12334342671.18.STEINBERGER
Posted: Sun Sep 13 14:47:54 1987
Date-Received: Mon, 14-Sep-87 03:51:51 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 49


    I have 2 questions concerning VAX C.  Thanks in advance to anyone who can
help.

Question 1: I wrote a short main routine (see below) to test a function.  One
of the inputs is an integer number, and the next input is a filename.  The
problem is that the scanf that reads the number apparently leaves a LF
character in a buffer that is then read by the code that is expecting the
filename.  Because it's a LF, I never get a chance to enter a filename (see
code).  My "kludgy" solution was to put the line "i = getchar()" after the
scanf to remove the LF character; when this is done the following lines that
get a filename work fine.  Am I missing something fundamental?  I've tried
using gets after the scanf and the result is the same, i.e. unless the "i =
getchar()" is there to remove the LF, gets doesn't "work" either.  Why does
scanf leave a LF character, or am I misinterpreting what's going on?  Are
there solutions other than using a getchar() call after a scanf that preceeds a
gets or getchar call?  The relevant code section is below:


	printf("\nEnter a string size: ");
	scanf("%d",&n_chars);
/*
                             clear NEWLINE char left after scanf 
*/
	i = getchar();          /* WHY DO I NEED THIS ? */

	printf("\nEnter a file to use: ");
	for (i=0; (input_file[i] = getchar()) != '\n'; i++);
        input_file[i] = '\0';

______________________________________________________________________________

Question 2: I am trying to read and write binary files similar to ones 
created by FORTRAN open statements (that produce sequential, unformatted,
fixed recordsize files).  Specifying "rb" in an fopen statement seems to
be enough to access existing files (using an fread call).  If I want to
create a new binary file with fixed-length records, which if any, of
the keywords on p 4-5 of the C RTL Ref Man are appropriate? Is "rfm=fix"
enough?  Do I need "mrs=size" as well, and if so, is size in units of bytes,
or longwords (like Fortran)?

Also, is there any reason to use the chapter 4 open and read or write
functions instead of the chapter 2 functions (fopen, fread and fwrite)?
______________________________________________________________________________


Ric Steinberger
steinberger@kl.sri.com
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