Gnu C ++宏__cplusplus标准符合? [英] Gnu C++ macro __cplusplus standard conform?
问题描述
Gnu C ++编译器似乎将 __ cplusplus
定义为 1
#include< iostream>
int main(){
std :: cout<< __cplusplus<< std :: endl;
}
打印 1
在标准c ++模式中使用gcc,在C ++ 0x模式中使用 gcc 4.3.4 和gcc 4.7.0。 / p>
C ++ 11 FDIS在<16>预定义宏名称[cpp.predefined] 中说明
在编译C ++翻译单元时,值201103L 定义的名称
__ cplusplus
(脚注:本标准的未来版本将以更大的值替换此宏的值。不合格的comp $ b pilers应使用最多五个十进制数字的值。)
旧的std C ++ 03也有类似的规则。
GCC故意将此设置为 1
,因为它是不合格?
通过该列表我认为如果我有一个C + + 11启用编译器,我可以使用 __ cplusplus
以检查便携式。但是使用 g ++ 这似乎不工作。我知道 ... EXPERIMENTAL ...
宏,但很好奇为什么 g ++ 定义 __ cplusplus
这样。
我的原始问题是在不同的空指针变体之间切换。像这样:
#if __cplusplus> 201100L
#define MYNULL nullptr
#else
#define MYNULL NULL
#endif
是否有一种简单而合理的便携式方式来实现此类切换?
这是固定大约一个月前(对于gcc 4.7.0)。错误报告提供了一个有趣的阅读: http://gcc.gnu.org/bugzilla/show_bug.cgi ?id = 1773
The Gnu C++ compiler seems to define __cplusplus
to be 1
#include <iostream>
int main() {
std::cout << __cplusplus << std::endl;
}
This prints 1
with gcc in standard c++ mode, as well as in C++0x mode, with gcc 4.3.4, and gcc 4.7.0.
The C++11 FDIS says in "16.8 Predefined macro names [cpp.predefined]" that
The name
__cplusplus
is defined to the value 201103L when compiling a C++ translation unit. (Footnote: It is intended that future versions of this standard will replace the value of this macro with a greater value. Non-conforming com- pilers should use a value with at most five decimal digits.)
The old std C++03 had a similar rule.
Is the GCC deliberatly setting this to 1
, because it is "non-conforming"?
By reading through that list I thought that I could use __cplusplus
to check in a portable way if I have a C++11 enabled compiler. But with g++ this does not seem to work. I know about the ...EXPERIMENTAL...
macro, but got curious why g++ is defining __cplusplus
this way.
My original problem was switch between different null-pointer-variants. Something like this:
#if __cplusplus > 201100L
# define MYNULL nullptr
#else
# define MYNULL NULL
#endif
Is there a simple and reasonably portable way to implement such a switch?
This was fixed about a month ago (for gcc 4.7.0). The bug report makes for an interesting read: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=1773
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