This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of LEWG status.
std::fixed ignores std::uppercaseSection: 30.4.3.3.3 [facet.num.put.virtuals] Status: LEWG Submitter: Jonathan Wakely Opened: 2024-04-30 Last modified: 2024-05-09
Priority: 3
View other active issues in [facet.num.put.virtuals].
View all other issues in [facet.num.put.virtuals].
View all issues with LEWG status.
Discussion:
In Table 114 – Floating-point conversions [tab:facet.num.put.fp]
we specify that a floating-point value should be printed as if by %f
when (flags & floatfield) == fixed.
This ignores whether uppercase is also set in flags,
meaning there is no way to use the conversion specifier %F
that was added to printf in C99.
That's fine for finite values, because 1.23 in fixed format has
no exponent character and no hex digits that would need to use uppercase.
But %f and %F are not equivalent for non-finite values,
because %F prints "NAN" and "INF" (or "INFINITY").
It seems there is no way to print "NAN" or "INF" using std::num_put.
Libstdc++ and MSVC print "inf" for the following code,
but libc++ prints "INF" which I think is non-conforming:
std::cout << std::uppercase << std::fixed << std::numeric_limits<double>::infinity();
The libc++ behaviour seems more useful and less surprising.
[2024-05-08; Reflector poll]
Set priority to 3 after reflector poll. Send to LEWG.
Proposed resolution:
This wording is relative to N4981.
Modify 30.4.3.3.3 [facet.num.put.virtuals] as indicated:
Table 114 – Floating-point conversions [tab:facet.num.put.fp] State stdioequivalentfloatfield == ios_base::fixed&& !uppercase%ffloatfield == ios_base::fixed%Ffloatfield == ios_base::scientific && !uppercase%efloatfield == ios_base::scientific%Efloatfield == (ios_base::fixed | ios_base::scientific)` && !uppercase%afloatfield == (ios_base::fixed | ios_base::scientific)%A!uppercase%gotherwise %G