| Summary: | support for printing/reading decimal numbers (_Decimal64) | ||
|---|---|---|---|
| Product: | glibc | Reporter: | Paul Zimmermann <zimmerma+gcc> |
| Component: | libc | Assignee: | Ulrich Drepper <drepper.fsp> |
| Status: | RESOLVED WONTFIX | ||
| Severity: | enhancement | CC: | glibc-bugs, vincent-srcware |
| Priority: | P2 | Flags: | fweimer:
security-
|
| Version: | unspecified | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | ||
The code is invalid. %f takes an argument of type double, not a _Decimal64. You need the D modifier (see WG14/N1312, 9.5 Formatted input/output specifiers), e.g. %Df. Vincent, you are right. With printf ("%.20Df\n", e) I get:
tarte% gcc bug.c
tarte% ./a.out
0.10000000000000000555
%.20Df
which is not very useful...
Paul
With a corrected code:
#include <stdio.h>
int main (void)
{
double d = 0.1;
_Decimal64 e = 0.1;
printf ("%.20f\n", d);
printf ("%Da\n", e);
printf ("%De\n", e);
printf ("%Df\n", e);
printf ("%Dg\n", e);
return 0;
}
currently gives:
0.10000000000000000555
%Da
%De
%Df
%Dg
Also, this doesn't matter now, but if accuracy needs to be taken into account (once this is implemented), one should use _Decimal64 e = 0.1dd; for the tests, instead of: _Decimal64 e = 0.1; *** Bug 11476 has been marked as a duplicate of this bug. *** This is what the printf hooks are for. I'm not going to add any such non-standard conversion. It far too dangerous a compability risk going forward. The conversion is currently non-standard, but it may become standard in the future. At that time, the status of this bug will have to be revised. (In reply to comment #6) > This is what the printf hooks are for. I'm not going to add any such > non-standard conversion. It far too dangerous a compability risk going forward. Dear Ulrich, please can you explain why this is "non-standard". With respect to which standard? Is _Decimal64 standard? Also, if someone provides changes to scanf/printf based on functions already existing in libbid or libdecnumber (currently used internally by gcc) for conversions between strings and decimal formats, would them be included in glibc? Subject: Re: support for printing/reading decimal numbers (_Decimal64) On Wed, 28 Apr 2010, zimmerma+gcc at loria dot fr wrote: > ------- Additional Comments From zimmerma+gcc at loria dot fr 2010-04-28 08:15 ------- > (In reply to comment #6) > > This is what the printf hooks are for. I'm not going to add any such > > non-standard conversion. It far too dangerous a compability risk going forward. > > Dear Ulrich, please can you explain why this is "non-standard". With respect to > which standard? Is _Decimal64 standard? A Technical Report Type 2 (such as TR 24732) is not a standard or an amendment to a standard. > Also, if someone provides changes to scanf/printf based on functions already > existing in libbid or libdecnumber (currently used internally by gcc) for > conversions between strings and decimal formats, would them be included in glibc? The functionality is in the libfdp add-on. This is an example of what the add-on mechanism is for; it doesn't need to be in the core libc. (I imagine the libdfp people will propose a scanf hook facility at some point to allow that part to be fully implemented in an add-on. One remaining DFP requirement relates to the predefined macro __STDC_DEC_FP__ but unfortunately my proposal for a change which would also allow that to be handled entirely within the add-on has stalled; see bug 10110.) |
as far as I know, the current glibc does not print/read decimal formats (_Decimal64 for example). Is there any plan to support this? Example code: #include <stdio.h> int main() { double d = 0.1; _Decimal64 e = 0.1; printf ("%.20f\n", d); printf ("%.20f\n", e); } gives: tarte% gcc bug.c tarte% ./a.out 0.10000000000000000555 0.00000000000000000000 We expect 0.10000000000000000000 for the second output.