Problems with evolving feature test macros?

[Joseph S. Myers]

On Tue, 11 Mar 2014, Michael Kerrisk (man-pages) wrote:

> Really? I could imagine it to be a source of quite some pain for
> programmers trying to write portable code, although I have no specific
> examples to cite. The point here is that programmer's are trying to
> write applications that are not Linux-specific, but are forced to

Then they shouldn't be using qecvt.  The whole ecvt/fcvt/gcvt function 
family is obsolete (the parts that were in POSIX as XSI extensions were 
marked LEGACY in the 2001 revision and removed in the 2008 revision), and 
qecvt never was even in POSIX.

For a portable application, you should avoid interfaces removed in newer 
standard versions, and probably avoid non-POSIX interfaces (_SVID_SOURCE 
and _BSD_SOURCE never were particularly well-defined sets of interfaces, 
at least not recently when __USE_MISC covers lots of stuff that's neither 
BSD nor SVID, and certainly weren't portably available sets of 
interfaces).  An application using _POSIX_C_SOURCE=200809L is a lot more 
likely to be portable (although not having reviewed the conformtest 
expectations against that version of POSIX, it's likely there are bugs 
beyond those currently shown by conformtest).

snprintf (not sprintf as suggested by the manpage) should be used instead 
of qecvt and the rest of that family.

-- 
Joseph S. Myers
joseph@codesourcery.com