__cplusplus对于C ++ 17的价值是什么? [英] What is the value of __cplusplus for C++17?

问题描述

我们正在尝试在C ++ 17及其更改为std::uncaught_exception 的情况下测试一些代码.我似乎无法让GCC提供__cplusplus的值:

We are trying to test some code under C++17 and its change to std::uncaught_exception. I can't seem to get GCC to provide the value of __cplusplus:

$ /opt/local/bin/g++ -std=c++17 -dM -E - </dev/null | grep __cplusplus
cc1: warning: command line option '-std=c++1z' is valid for C++/ObjC++ but not for C
$

并且:

$ /opt/local/bin/g++ --version
g++-mp-6 (MacPorts gcc6 6.1.0_0) 6.1.0
Copyright (C) 2016 Free Software Foundation, Inc.

使用C ++ 17时__cplusplus的值是什么?

What is the value of __cplusplus when using C++17?

推荐答案

使用C ++ 17时__cplusplus的值是什么?

根据标准草案 N4594 §16.8/p1预定义的宏名称[cpp.predefined] (重点矿):

以下宏名称应由实现定义: __cplusplus名称__cplusplus定义为值 201402L ，当编译C ++转换单元时. ¹⁵⁶

The following macro names shall be defined by the implementation: __cplusplus The name __cplusplus is defined to the value 201402L when compiling a C++ translation unit.¹⁵⁶

_{156)本标准的未来版本旨在 用更大的值替换此宏的值.不合格 编译器应使用最多包含五个十进制数字的值.}

_{156) 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.}

但是，为C ++ 14标准指定了相同的值.显然，C ++ 17标准尚未设置官方/标准__cplusplus值.

However the same value is appointed for the C++14 standard. Apparently it seems so, that there's no official/standard __cplusplus value set yet for the C++17 standard.

在GCC版本6.1和7.0中，值更改为 201500

In GCC versions 6.1 and 7.0 the value is changed to 201500

实时演示

在Clang 3.8版和3.9版中，该值保持不变 201406 .

In Clang version 3.8 and 3.9 the value is unchanged 201406.

因此，您需要稍等一会儿才能看到标准值.

Consequently, you'll have to wait a little bit for the standard value to come out.

根据C ++标准§19.8/p1预定义的宏名称[cpp.predefined] (强调矿井):

According to the C++ standard §19.8/p1 Predefined macro names [cpp.predefined] (Emphasis Mine):

₁ 以下宏名称应由 实施:

₁ The following macro names shall be defined by the implementation:

__cplusplus整数常量 201703L .

因此，使用C ++ 17时__cplusplus的值应为 201703L .

Thus, the value of __cplusplus when using C++17 shall be 201703L.

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