我需要一个extern“C”块包括标准C头？ [英] Do I need an extern "C" block to include standard C headers?

问题描述

我需要一个 externC{} 块，以在C ++程序中包含标准C头。只考虑在C ++中没有对应项的标准C头。

例如：

 code> externC{
 #include< fcntl.h> 
 #include< unistd.h> 
} 
  

解决方案

<$ c C ++中的$ c>< fcntl.h> 和< unistd.h> 不是由标准指定的（因为它们也不是部分C89标准）。也就是说，我从来没有见过一个平台，他们（a）存在，（b）实际上需要包装在 externC b
$ b

< stdio.h> ，< math.h> ，而其他标准C头由C ++ 03标准的D.5节指定。它们不需要 externC包装器块，并且将它们的符号转储到全局命名空间中。但是，附件D中的所有内容都已废弃。

这些标题的规范C ++形式是< cstdio> ，< cmath> 等，并且它们由C ++标准的第17.4.1.2（3）节指定：

 < cassert> < ciso646> < csetjmp> < cstdio> < ctime> < cctype> < climits> 
< csignal> < cstdlib> < cwchar> < cerrno> < clocale> < cstdarg> ;. < cstring> 
< cwctype> 
  

除第18至27条所述外，
cname应与相应的标题name.h的相同，如ISO / IEC 9899：1990编程语言C（第7条）中规定的
或
ISO / IEC：1990编程语言-C修改1：C完整性，（条款
7），如果合适，如同通过包含。然而，在C ++标准库
中，声明和定义（除了
定义为C中的宏之外的名称）在
命名空间std的命名空间范围（3.3.5）中。

因此，使用标准的，非弃用的，规范的方式（例如） printf 在C ++中是 #include< cstdio> 然后调用 std :: printf 。

Do I need an extern "C" {} block to include standard C headers in a C++ program. Only consider standard C headers which do not have counterparts in C++.

For example:

extern "C" {
 #include <fcntl.h>
 #include <unistd.h>
}

解决方案

The behavior of <fcntl.h> and <unistd.h> in C++ is not specified by the standard (because they are also not part of the C89 standard). That said, I have never seen a platform where they (a) exist and (b) actually need to be wrapped in an extern "C" block.

The behavior of <stdio.h>, <math.h>, and the other standard C headers is specified by section D.5 of the C++03 standard. They do not require an extern "C" wrapper block, and they dump their symbols into the global namespace. However, everything in Annex D is "deprecated".

The canonical C++ form of those headers is <cstdio>, <cmath>, etc., and they are specified by section 17.4.1.2 (3) of the C++ standard, which says:

<cassert> <ciso646> <csetjmp> <cstdio> <ctime> <cctype> <climits>
<csignal> <cstdlib> <cwchar> <cerrno> <clocale> <cstdarg> <cstring>
<cwctype>

Except as noted in clauses 18 through 27, the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C (Clause 7), or ISO/IEC:1990 Programming Languages—C AMENDMENT 1: C Integrity, (Clause 7), as appropriate, as if by inclusion. In the C++ Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std.

So the standard, non-deprecated, canonical way to use (e.g.) printf in C++ is to #include <cstdio> and then invoke std::printf.

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