Re: sprintf() error (compiled by VC++)

[Ethan M. <merritt@u.washington.edu>]

On Thursday, October 06, 2011 03:46:13 pm Hans-Bernhard Bröker wrote:
> On 06.10.2011 10:01, Shigeharu TAKENO wrote:
> 
> > I saw that gnuplot.exe of CVS version compiled by VC++ reports
> [...]
> >    foo = sprintf("%40d %40d %40d %40d %40d %40d",1,2,3,4,5,6)
> >          ^
> >    "stringvar.dem", line 59: undefined value
> 
> For what it's worth: this program doesn't appear in gnuplot.exe compiled 
> by Open Watcom.
> 
> > The gnuplot show no erorr message for the command
> >
> >    foo = sprintf("%83d",1)
> >
> > but it show the same error message above for the command
> >
> >    foo = sprintf("%84d",1)
> 
> This doesn't cause problem either.
> 
> The root of the problem appears to be the buffer size computation and 
> subsequent realloc()ation in f_sprintf().  The number 84 is magic 
> because it's 84 plus the length of the format string "%84d".  Go figure.

The problem occurs when the platform/compiler does not support snprintf.
f_sprintf() has:

#ifdef HAVE_SNPRINTF
        /* Use the format to print next arg */
    ... this code works fine ...
#else
        /* FIXME - this is bad; we should dummy up an snprintf equivalent */
    ... this code triggers a buffer overflow if the format width is too large
#endif

So the FIXME comment is correct.
	
	Ethan

-- 
Ethan A Merritt
Biomolecular Structure Center,  K-428 Health Sciences Bldg
University of Washington, Seattle 98195-7742