Re: [HACKERS] snprintf causes regression tests to fail

Nicolai Tufar <ntufar(at)gmail(dot)com> writes:
>> Having looked at the current snprintf.c, I don't actually believe that
>> it works at all in the presence of positional parameter specs.

> It picks up arguments in order of appearance, places them in
> array then shuffles them according to %n$ positional parameter.
> I checked it with in many different combinations, it works!

Did you try combinations of parameters of different sizes? For instance

snprintf(..., "%g %d", doubleval, intval);
and
snprintf(..., "%2$d %1$g", doubleval, intval);

You cannot pick this up in order of appearance and expect it to work.
It might fail to fail on some machine architectures, but it's not going
to be portable.

>> On the other side of the
>> coin, the hardwired 4K limit in printf() is certainly *not* enough.

> How would one solve this issue. Calling malloc() from a print function
> would be rather expensive.

printf shouldn't use a buffer at all. I was thinking in terms of
passing around a state struct like

typedef struct {
char *output;
char *end;
FILE *outfile;
} printf_target;

and making dopr_outch look like

static void
dopr_outch(int c, printf_target *state)
{
if (state->output)
{
if (state->end == NULL || state->output < state->end)
*(state->output++) = c;
}
else
fputc(c, state->outfile);
}

regards, tom lane