[Wylug-help] C++ code

[Roger Leigh]

Roger Greenwood <rg@nthong.freeserve.co.uk> writes:

> The problem is buffers (i think). The code snippet following gets a
> number from stdin, by way of any string entry. The commented out bits
> have been left in so you can see where I am.
>
> What happens is that the number entered seems to leave an entry in the
> buffer so that the next question is already answered (incorrectly).

The buffer isn't cleared when you have read from it, which shouldn't
be a problem.  However, I've seen this in the past, but can't remember
the reason (I think it's the line feed at the end of the string).
I've attached the code I use in gimp-print (for the escputil tool) at
the end of the message.  This code has fully tested and working
fgets() and readline() modes, which are fully commented (it's fairly
obvious which parts use fgets()).  You'll also need to remove the _()
i18n bits.  In case you wonder why input is static, that's so the
caller doesn't need to care about memory allocation, but they can
duplicate it if they need.

I would suggest using libreadline instead of gets/fgets, but you
*must* have GPL licensed your code to link with it.

> int getnum(void)
> {
> 	int num;
> 	double numd;
> 	char entry[80];
        const char* entry = NULL;

> 	int valid = FALSE;
> 	int exit = FALSE;
> 	double dummy = 0;
> 	double fraction;
> 	do
> 	{
> 		fgets(entry,5,stdin);

                while (!entry)
                  entry = readline("Enter a real number: ");
                /* link with -lreadline; your code must be GPLed */

> 		numd = atof(entry);
> 		fraction = modf(numd,&dummy);

                free (entry);
                entry = NULL;

> 		if (fraction !=0)
                   (fraction)

> 		{
> 			cout <<"\nEntry must be a whole number - decimals not allowed ";
> 			numd = -1;
> 			cout <<"\n\nPlease try again :- ";
> 		}
> 		if (numd == 0) exit = TRUE;
                if (!numd)
                   exit = 1;

> 		if (numd >0)
> 		{
> 			if (numd <= MAXINT)
> 			{
> 				valid = TRUE;
                                valid = 1;

> 			}
> 			else
> 			{
> 				cout << "\nEntry must be less than "<< MAXINT;
> 				cout << "\n\nPlease try again :- ";
                                /* not valid C! */

> 			}
> 		}
> 	}
> 	while ((valid == FALSE) && (exit == FALSE));
               (!valid && !exit)

> 	if (exit == TRUE)
           (exit)

> 	{
> 		num = 0;
> 	}
> 	else
> 	{
> 		num = int(numd);
                      (int) numd; /* no int() function call! */

> 	}
> 	return(num);
        return num; /* return is not a function call */

> }

>From an aesthetic point-of-view, I don't like the TRUE and FALSE
macros; just use if (valid) or if (!valid) which are much safer and
easier to read (if TRUE is 0, FALSE is !0, not 1 and vice-versa).  The
definition of true and false can also change:

if (exit)
  exit(EXIT_SUCCESS);
Here, exit is 1, which is FALSE!!  From the code above, I guess you
used the opposite values, which is /not/ obvious!

I would also check the return type of /every/ libc function (except
perhaps printf) and print a diagnostic error message if it returns a
failure:

fprintf(stderr, "%s: Foo happened: %s\n", argv[0], strerror(errno));
(If you only use GNU ld/GNU libc, you can use program_invocation_name
and program_invocation_short_name instead of argv[0].)

HTH,
Roger


----do_get_input()----
char *
do_get_input (const char *prompt)
{
        static char *input = NULL;
#if (HAVE_LIBREADLINE == 0 || !defined HAVE_READLINE_READLINE_H)
        char *fgets_status;
#endif
        /* free only if previously allocated */
        if (input)
        {
                free (input);
                input = NULL;
        }
#if (HAVE_LIBREADLINE > 0 && defined HAVE_READLINE_READLINE_H)
        /* get input with libreadline, if present */
        input = readline ((char *) prompt);
        /* if input, add to history list */
#ifdef HAVE_READLINE_HISTORY_H
        if (input && *input)
        {
                add_history (input);
        }
#endif
#else
        /* no libreadline; use fgets instead */
        input = xmalloc (sizeof (char) * BUFSIZ);
        memset(input, 0, BUFSIZ);
        printf ("%s", prompt);
        fgets_status = fgets (input, BUFSIZ, stdin);
        if (fgets_status == NULL)
        {
                fprintf (stderr, _("Error in input\n"));
                return (NULL);
        }
        else if (strlen (input) == 1 && input[0] == '\n')
        {
                /* user just hit enter: empty input buffer */
                /* remove line feed */
                input[0] = '\0';
        }
        else
        {
                /* remove line feed */
                input[strlen (input) - 1] = '\0';
        }
#endif
        return (input);
}
----end do_get_input()----


--
Roger Leigh
                "Liberty and Livelihood" - Support the Countryside Alliance
                Need Epson Stylus Utilities? http://gimp-print.sourceforge.net/
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