Re: better snprintf replacement, anyone?

[peter.jeremy () ALCATEL COM AU (Peter Jeremy)]

On Tue, 22 Jul 1997 10:19:54 -0400, der Mouse <mouse () RODENTS MONTREAL QC CA>
wrote:
> My reaction to this is "not using punched cards makes it hard to port
> to (other) legacy systems".  The point beyond which a system is so
> legacy it's not worth even trying to support it, for me, includes
> systems without calls like snprintf.
Sun would probably not be totally pleased with having Solaris 2.5.1(*)
referred to as a legacy OS.  I don't have ready access to other
current commercial C libraries.  There's also the problem that (as far
as I know) [v]snprintf() is not part of the Standard C Library.

(*) Solaris 2.5.1 does include [v]snprintf, but only as `private'
    routines with non-standard names.  The routines weren't present
    at all prior to Solaris 2.5.

On Tue, 22 Jul 1997 00:57:11 -0600, Theo de Raadt <deraadt () CVS OPENBSD ORG>
wrote:
> On 22nd July, Steve Coile wrote:
> > I would imagine that there are only a few cases were a program coulnd't
> > pre-determine the length of a string that would be generated by sprintf()
> > and malloc() enough memory to contain it all.

> Let me give you an example of what you suggest:
>
>        if (strlen(a) + 1 + 10 + 3 + 1 + 10 + 4*sizeof(long) + 1 + strlen(b) +
>            1 + strlen(c) + 2 >= sizeof buf);
>                sprintf(buf, "%s %d see %d %lx %s %s\n", a, i, j, p,
>                    b, c);
>        else
>                goto bail; /* I really just wanted to truncate the string... */

As a comment to support Theo's point of view, it's worth noting that
the above example includes about 6 errors.  I realize Theo probably
whipped it up off the top of his head, but it does demonstrate the
difficulty of this approach.  It should be something like:

#define N_DEC_DIGIT(type)       ((((sizeof(type) * 8 - 1) * 30103 + 99999) \
                                 / 100000) + 1)

        if (strlen(a) + 1 + N_DEC_DIGIT(int) + 5 + N_DEC_DIGIT(int) + 1 +
            2*sizeof(long) + 1 + strlen(b) + 1 + strlen(c) + 2 <= sizeof buf)
        {
                sprintf(buf, "%s %d see %d %lx %s %s\n", a, i, j, p, b, c);
        } else {
                goto bail; /* I really just wanted to truncate the string... */
        }

(For those puzzled about N_DEC_DIGIT: log10(2) ~= .30103 and the sign bit
doesn't count).

Peter
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Peter Jeremy (VK2PJ)                    peter.jeremy () alcatel com au
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