为什么C ++标准没有提到__STDC_IEC_559__？ [英] Why does the C++ standard not mention __STDC_IEC_559__?

问题描述

根据C ++ 11标准[c.math]，< cmath> 头与标准C库头 math.h> 。

（当然，有几个区别，---命名空间，重载等等---但这里可以忽略。）

根据C99标准附录F，定义 __ STDC_IEC_559 __ 的实现应符合附录F中的规范。

例如。如果两个参数都为零，则 atan2 可能会导致域错误，但如果定义 __ STDC_IEC_559 __ p>

在C99中，许多行为也取决于是否定义 __ STDC_IEC_559 __ 。

但是，似乎在C ++ 11标准中没有提及 __ STDC_IEC_559 __ 。

如果是这样，实现符合附件F中的规范？

我认为 std :: numeric_limits< T> :: is_iec559（）

解决方案

C ++标准（n3797）包括C标准库，见参考文件s1.2 / 2。

ISO / IEC 9899：1999第7条和ISO / IEC 9899：1999 / Cor.1中第7条所述的库： 2001
和ISO / IEC 9899：1999 / Cor.2：2003的第7条以下称为C标准库。

18到30，在C.4中，C标准库是C ++标准
库的子集。

标准中没有提到该符号，我不会期望它被定义，因为它似乎是标准C的特定。通过不定义该符号，C ++不受附件F的内容的约束。

相反，C ++标准包含了更多类似C ++的形式的多个IEC 559提及。例如

对于 is_iec559！= false

在18.3.2.4/56中有具体的提及。

static constexpr bool is_iec559;

当且仅当类型符合IEC 559 standard.218时才为true

对所有浮点类型都有意义。

我认为C ++包含所有相同能力（或缺乏），但适应C ++世界。

According to C++11 standard [c.math], the <cmath> header is same as Standard C library header <math.h>.
(Of course, there are several differences, --- namespace, overloads etc. --- but these can be ignored here.)
And according to C99 standard annex F, "An implementation that defines __STDC_IEC_559__ shall conform to the specifications in" the annex F.

Ex. The atan2 may cause a domain error if both arguments are zero, but It must not if __STDC_IEC_559__ is defined.

In C99, many behavior is also dependent on whether __STDC_IEC_559__ is defined or not.

However, it seems that __STDC_IEC_559__ is not mentioned anywhere in C++11 standard.
If so, shall a C++ implementation conform to the specifications in the annex F?

I think that std::numeric_limits<T>::is_iec559() is a substitute, but it seems to mention about only type.

解决方案

The C++ standard (n3797) includes the C standard library by reference, see s1.2/2.

The library described in Clause 7 of ISO/IEC 9899:1999 and Clause 7 of ISO/IEC 9899:1999/Cor.1:2001 and Clause 7 of ISO/IEC 9899:1999/Cor.2:2003 is hereinafter called the C standard library.

With the qualifications noted in Clauses 18 through 30 and in C.4, the C standard library is a subset of the C++ standard library.

The standard contains no mention of that symbol, and I would not expect it be defined, since it appears to be specific to Standard C. By not defining that symbol, C++ is not bound by the contents of Annex F.

Instead the C++ standard contains multiple mentions of IEC 559 in a rather more C++-like form. For example,

Shall be true for all specializations in which is_iec559 != false

There is a specific mention in 18.3.2.4/56.

static constexpr bool is_iec559;

True if and only if the type adheres to IEC 559 standard.218

Meaningful for all floating point types.

I think it would be fair to say that C++ includes all the same capabilities (or lack of them), but adapted to the C++ world.

这篇关于为什么C ++标准没有提到__STDC_IEC_559__？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！