Will __GXX_EXPERIMENTAL_CXX0X__ go away?

Will __GXX_EXPERIMENTAL_CXX0X__ go away?

[Patrick Horgan]

I'm using the following in a header that uses typeof and needs to build
in code that builds with -std=c++0x or the default -std=c++98.  Can I
leave it and forget it, or will eventually the compiler's use of c++0x
features no longer be experimental?  How do I future proof it?

#ifdef __GXX_EXPERIMENTAL_CXX0X__
#define typeof decltype
#endif


Patrick

Re: Will __GXX_EXPERIMENTAL_CXX0X__ go away?

[Jonathan Wakely]

On 25 May 2011 07:44, Patrick Horgan wrote:
> I'm using the following in a header that uses typeof and needs to build
> in code that builds with -std=c++0x or the default -std=c++98.  Can I
> leave it and forget it, or will eventually the compiler's use of c++0x
> features no longer be experimental?  How do I future proof it?
>
> #ifdef __GXX_EXPERIMENTAL_CXX0X__
> #define typeof decltype
> #endif

Yes it will go away at some point.  The portable way to detect C++0x support is:

#if __cplusplus >= 201103L

Re: Will __GXX_EXPERIMENTAL_CXX0X__ go away?

[Jonathan Wakely]

On 25 May 2011 09:19, Jonathan Wakely wrote:
> On 25 May 2011 07:44, Patrick Horgan wrote:
>> I'm using the following in a header that uses typeof and needs to build
>> in code that builds with -std=c++0x or the default -std=c++98.  Can I
>> leave it and forget it, or will eventually the compiler's use of c++0x
>> features no longer be experimental?  How do I future proof it?
>>
>> #ifdef __GXX_EXPERIMENTAL_CXX0X__
>> #define typeof decltype
>> #endif
>
> Yes it will go away at some point.  The portable way to detect C++0x support is:
>
> #if __cplusplus >= 201103L

Actually portable is the wrong word, since G++ doesn't actually
conform to that requirement - but it's the method specified by the
standard, so other compilers should conform to it and G++ should do
one day too.

Re: Will __GXX_EXPERIMENTAL_CXX0X__ go away?

[Patrick Horgan]

On 05/25/2011 01:21 AM, Jonathan Wakely wrote:
> On 25 May 2011 09:19, Jonathan Wakely wrote:
>> On 25 May 2011 07:44, Patrick Horgan wrote:
>>> I'm using the following in a header that uses typeof and needs to build
>>> in code that builds with -std=c++0x or the default -std=c++98.  Can I
>>> leave it and forget it, or will eventually the compiler's use of c++0x
>>> features no longer be experimental?  How do I future proof it?
>>>
>>> #ifdef __GXX_EXPERIMENTAL_CXX0X__
>>> #define typeof decltype
>>> #endif
>> Yes it will go away at some point.  The portable way to detect C++0x support is:
>>
>> #if __cplusplus >= 201103L
> Actually portable is the wrong word, since G++ doesn't actually
> conform to that requirement - but it's the method specified by the
> standard, so other compilers should conform to it and G++ should do
> one day too.
>
Yeah, the current draft (N3242) has this:
16.8 Predefined macro
names                                               [cpp.predefined]
1 The following macro names shall be defined by the implementation:
_ _ cplusplus
The name _ _ cplusplus is defined to the value 201103L when compiling a
C++ translation unit.155
155) It is intended that future versions of this standard will replace
the value of this macro with a greater value. Non-conforming compilers
should use a value with at most five decimal digits.

right now gcc defines __cplusplus as 1, so maybe something like?

#if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
#define typeof decltype
#endif

Patrick

Re: Will __GXX_EXPERIMENTAL_CXX0X__ go away?

[Jonathan Wakely]

The current draft is n3290 but apart from that, yes that should detect
C++0x support

I hope that gcc will eventually define __cplusplus correctly too