[cfe-commits] [patch] Conditionalize use of 'long long' for libc++

[Dimitry Andric]

On 2012-11-26 17:59, Howard Hinnant wrote:
> On Nov 25, 2012, at 12:24 PM, Dimitry Andric <dimitry at andric.com> wrote:
>> When using libc++ headers on FreeBSD, in combination with -std=c++98,
>> -ansi or -std=c++03, the long long type is not supported.  So in this
>> case, several functions and types, like lldiv_t, strtoll(), are not
>> declared.
>>
>> The attached patch conditionalizes those types and functions for libc++,
>> using a _LIBCPP_HAS_NO_LONG_LONG define.  This can easily be extended
>> to other operating systems.
...
> Thanks for the patch Dimitry.
>
> long long is used extensively throughout the libc++ headers.  I'm counting over 200 uses (just a quick search which also picks up comments).  The reason long long isn't already guarded is because libc++ wasn't meant to serve as a C++98/03 implementation.

I understand; on FreeBSD, we indeed build the libc++ implementation with
-std=c++0x.  But the idea is that if there is a relatively simple way of
using just the *headers* in that mode, it would be nice to have.


> I'm wondering if your patch actually expands the usability of libc++ on FreeBSD.  It only guards 2 of the 14 or so headers that use long long.  I'm hesitant both to put in a partial solution, and also to clutter the library by guarding all uses.
>
> Can you clarify what differentiates <cstdlib> and <cwchar> from all of the other headers that use long long?

When you use clang and gcc in -std=c++98 mode, they don't actually
forbid using the long long type, unless you are using -pedantic (and
then you get what you ask for :).  So there really isn't a problem in
using the type throughout the headers, and there is no need to
conditionalize all of the uses.

The reason <cstdlib> and <cwchar> are special, at least on FreeBSD, is
that the corresponding C headers <stdlib.h> and <wchar.h> do not declare
some macros, types, functions when compiling for __cplusplus < 201103L.
Namely, the following:

macros:
   ULLONG_MAX
   LLONG_MAX
   LLONG_MIN
types:
   lldiv_t
functions:
   atoll()
   llabs()
   lldiv()
   strtoll()
   strtoull()
   wcstoll()
   wcstoull()

The patch I posted just conditionalizes these specific types and
functions; the macros are only referenced in a comment in <climits>, so
there is no need to do anything about those.

Note, Linux (actually glibc) also has a define, __GLIBC_HAVE_LONG_LONG,
used to conditionalize a similar list of functions like atoll, strtoll,
etc.  So the approach in my could also work for the Linux case.  And
I'll assume something like this is also used in the OSX headers...