将std :: tr1导入std-是否合法?会提高便携性吗? [英] Importing std::tr1 into std - is it legal? Does it improve portability?

问题描述

我有C ++ 03代码，如下所示:

I have C++03 code that looks like this:

#include <boost/tr1/unordered_map.hpp>
...
std::tr1::unordered_map<std::string, int> mystuff;
...

我开始怀疑，如果以后将代码转换为C ++ 11时会遭受痛苦，(我想)它没有std::tr1::unordered_map但却具有std::unordered_map.所以我想出了以下技巧:

I started to wonder that i would suffer later if/when i convert my code to C++11, which (i guess) doesn't have std::tr1::unordered_map but has std::unordered_map instead. So i came up with the following hack:

namespace std
{
    using namespace ::std::tr1;
}
...
std::unordered_map<std::string, int> mystuff; // no tr1 now!
...

是否合法(也许禁止将物料导入到std中)?它将使与C ++ 11代码的移植/互操作变得更容易吗?

Is it legal (maybe importing stuff into std is forbidden)? Will it make it easier to port/interoperate with C++11 code?

推荐答案

您不应触摸std命名空间:即使现在可以使用，也可能会在以后导致严重的头痛(使用新版本的编译器时，不同的编译器等).

You should not touch the std namespace: even if it works now, it can cause severe headaches later (with a new version of the compiler, on a different compiler, etc).

更新:引用标准(C ++ 2003，第17.4.3.1节保留名称")(找到

Update: Quote from the standard (C++ 2003, Section 17.4.3.1 "Reserved names") (found here):

对于C ++程序，除非另有说明，否则将声明或定义添加到名称空间std或名称空间std中的名称空间未定义.程序可以将任何标准库模板的模板专业化添加到名称空间std.除非声明依赖于用户定义的外部链接类型，并且除非该专业化满足原始模板的标准库要求，否则标准库模板的这种专业化(全部或部分)会导致未定义的行为. [强调我的]

It is undefined for a C++ program to add declarations or definitions to namespace std or namespaces within namespace std unless otherwise specified. A program may add template specializations for any standard library template to namespace std. Such a specialization (complete or partial) of a standard library template results in undefined behavior unless the declaration depends on a user-defined type of external linkage and unless the specialization meets the standard library requirements for the original template. [emphasis mine]

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