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Date: Mon, 24 Nov 1997 13:20:27 +1100 (EST)
From: Andrew Cagney <cagney@tpgi.com.au>
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To: FreeBSD-gnats-submit@FreeBSD.ORG
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Subject: bin/5135: scanf accepts %Lg but treates it as %g
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>Number:         5135
>Category:       bin
>Synopsis:       scanf accepts %Lg but treates it as %g
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Nov 23 22:30:01 PST 1997
>Last-Modified:
>Originator:     Andrew Cagney
>Organization:
>Release:        FreeBSD 2.2.5-RELEASE i386
>Environment:

Vanilla 2.2.5

>Description:

Burried away in the scanf documentation is:

     L       Indicates that the conversion will be efg and the next pointer is
             a pointer to long double. (This type is not implemented; the L
             flag is currently ignored.)

to be more precise, it assigns a `%g' value (32 bit float or single)
to a `%Lg' destination (80 bit long double).  I'm sorry but doing this
is worse than stupid!

>How-To-Repeat:

One example, all GDB floating point is broken:

        $ gdb
        ...
        (gdb) print 1.0
        $1 = 0

If you trace it through, c-exp.c:parse_number calls sscanf(...%Lg...).

>Fix:
	

For FreeBSD:

o       modify scanf so that for, %Lg (long double) it parses
        it as %lg (double) then extends/stores it as a long double.

o	Remove all support for %Lg in both printf and scanf.

	Some software (eg gdb) tests printf ("%Lg") and then assumes
	scanf also works.  Consequently it is an all or nothing afair
	:-)


For GDB:

I'll see if I can get GDB changed so that its configure script
separately checks for support of %Lg in scanf and printf.


Have a nice day.

			Andrew
>Audit-Trail:
>Unformatted: