Charles Mills wrote:
I'd like to format fixed point decimal (packed, in other words) numbers in a
common subroutine that would be passed the precision and scaling. Can
printf() and friends take '*' and then a passed integer for its (n,p) values
- analogous to the way printf() width and precision may be specified?
My initial experiment failed but I'd like a clue whether it's mission
impossible or fat fingers.
Hi again Charles,
I just had this thought that might work for you. You can build
the %D specification yourself - something like:
_Decimal(X,Y) d; /* where X and Y were, for example macros that */
/* expand to valid constant integers
- but unknown */
/* to this routine. */
char fmt[20];
sprintf(fmt,"d is %%D(%d,%d)\n", digitsof(d), precisionof(d));
printf(fmt, d);
I think, in practice, as the #-of-digits and precision specifications
in a _Decimal data declaration must be constants, any program is going
to know the values a-priori. But, in the event of macros, etc.. it's
possible
for the programmer to not know what values may eventually be used
(even though, at compile-time, these are definitionally constant.)
Of course, there would be the general pointer-to-_Decimal problem to.
For example, here's a routine that accepts a pointer to the _Decimal value,
and the number-of-digits and precision of that _Decimal value and then
prints it out with printf(); but even in that case, because %D wants
the _value_
of the _Decimal data (not a pointer to it) you still have do some
shanigans.
(I only show the first 8 possibilities - would need to expand this for
all 31-digit
possibilities):
void
printd(void *dec, int digits, int prec)
{
_Decimal(1,0) d1; _Decimal(2,0) d2; _Decimal(3,0) d3;
_Decimal(4,0) d4;
_Decimal(5,0) d5, _Decimal(6,0) d6; _Decimal(7,0) d7,
_Decimal(8,0) d8;
char fmt[20];
switch(digits) {
case 1: memcpy(&d1, dec, 1); break; case 2: memcpy(&d2,dec,2);
break;
case 3: memcpy(&d3, dec, 2); break; case 4: memcpy(&d4, dec,
3); break;
case 5: memcpy(&d5, dec, 3); break; case 6: memcpy(&d6, dec,
4); break;
case 7: memcpy(&d7, dec, 4); break; case 8: memcpy(&d8, dec,
5); break;
}
sprintf(fmt, "dec is %%D(%d,%d)", digits, prec);
switch(digits) {
case 1: printf(fmt, d1); break; case 2: printf(fmt, d2); break;
case 3: printf(fmt, d3); break; case 4: printf(fmt, d4); break;
case 5: printf(fmt, d5); break; case 6: printf(fmt, d6); break;
case 7: printf(fmt, d7); break; case 8: printf(fmt, d8); break;
}
}
This little trick, of formatting the format string or something similar
might be a good approach.
- Dave Rivers -
--
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