Re: How do I find when the diagnostic pragmas first came into gcc?

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 11 January 2011 07:52, Patrick Horgan wrote:
> int
> main()
> {
> Â? Â?size_t a = 7;
> Â? Â?int b = -3;
> #if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__
>>= 6))

I use something like this:

#if ((__GNUC__*100)+__GNUC_MINOR__) >= 406

If the macros aren't defined they will evaluate to zero.

> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wsign-compare"
> #endif


> Ugly but effective.

I wrote this last week, which tames some of the ugliness:

#if ((__GNUC__ * 100) + __GNUC_MINOR__) >= 405
# define GCC_DIAG_DO_PRAGMA(x) _Pragma (#x)
# define GCC_DIAG_PRAGMA(x) GCC_DIAG_DO_PRAGMA(GCC diagnostic x)
# if ((__GNUC__ * 100) + __GNUC_MINOR__) >= 406
#  define GCC_DIAG_OFF(x) GCC_DIAG_PRAGMA(push) \
     GCC_DIAG_PRAGMA(ignored x)
#  define GCC_DIAG_ON(x) GCC_DIAG_PRAGMA(pop)
# else
#  define GCC_DIAG_OFF(x) GCC_DIAG_PRAGMA(ignored x)
#  define GCC_DIAG_ON(x)  GCC_DIAG_PRAGMA(warning x)
# endif
#else
# define GCC_DIAG_OFF(x)
# define GCC_DIAG_ON(x)
#endif

That gives convenient macros which are used like so:

GCC_DIAG_OFF("-Wsign-compare")
   if (a < b) {
GCC_DIAG_ON("-Wsign-compare")
       std::cout << "a<b\n";
   }

The macros use push/pop for 4.6+, or for 4.5 they just change the
behaviour to "ignored" then back to "warning".   They expand to
nothing for older versions of GCC or for non-GCC compilers.

The 4.5 behaviour is wrong if e.g. -Werror=sign-compare was being
used, because GCC_DIAG_ON re-enables a warning not an error. For my
purposes that was sufficient, it's probably not acceptable for library
code.

I've been using this for super-strict compilations with a modified GCC
that has extra warnings I've added. One of my extra warnings has too
many false positives, so I really needed to disable some known
warnings I wasn't going to fix.

For these super-strict builds, I need to temporarily disable warnings
in third-party libraries which I can't or don't want to change (Boost
in particular.) To do this I include them with -isystem instead of -I,
which has the same effect as adding the system_header pragma to them.
That allows me to make warnings fatal with -Werror without having to
worry about errors in code I don't own.