什么是C ++ 98等效的自动迭代器参考？ [英] What's the C++98 equivalent of the auto iterator reference?

问题描述

我的开发环境有RHEL 5.8，它不支持GCC 4.8+现代（C ++ 11 +）编译器。我预计有一天我们会到那里，所以我有一个头文件，其中我定义宏基于C ++ 11支持级别，所以我可以这样做：

My development environment has RHEL 5.8 which does not support GCC 4.8+ modern (C++11+) compilers. I anticipate that someday we'll get there, so I have a header file where I define macros based on C++11 support levels so I can do something like this:

#if defined(CPP11_auto_type_inference) && defined(CPP11_range_based_for_loops)
  for (auto vit : args)
#else
  std::vector<std::string>::const_iterator vit, vend;
  for (vend=args.end(),vit=args.begin(); vit != vend; ++vit)
#endif
  { // process arguments...
    std::cout << "Processing \"" << *vit << '"' << std::endl;
    . . .
  } // end "process arguments" loop

在C ++ 98中，相当于迭代器引用（或者更准确地说dereferenced iterator？），如下所示：

So, what I'm trying to do in C++98 is the equivalent of the iterator reference (or is it more accurate to say "a dereferenced iterator"?), like below:

for (auto& it : args)
  std::cout << "Processing \"" << it << '"' << std::endl;

对于我的生活，我不知道如何获得一个解引用的迭代器在C ++ 98。我可以模拟，如下：

For the life of me, I cannot figure out how to get a dereferenced iterator (or iterator reference) in C++98. I can simulate, as below:

#if defined(CPP11_auto_type_inference) && defined(CPP11_range_based_for_loops)
  for (auto& it : args) {
#else
  std::vector<std::string>::const_iterator vit, vend;
  for (vend=args.end(),vit=args.begin(); vit != vend; ++vit) {
    std::string it(*vit);
#endif
    std::cout << "Processing \"" << it << '"' << std::endl;
    . . .
  }

...但我真的希望这不是答案。

... but I'm really hoping that is not the answer.

的C ++ 98等价物是（auto& it：vec），还是不可能？是否只能模拟它，但是取消引用迭代器并在每次迭代中创建一个副本？

What is the C++98 equivalent of for (auto& it : vec), or is it not possible? Is it only possible to "simulate" it but dereferencing the iterator and creating a copy each iteration?

如果是这种情况，覆盖C ++ 11 auto& 语法？ （我不得不相信这是不是。）无论如何，使用（auto& it：vec）

And if that be the case, is that what is going on "under the covers" with C++11 auto& syntax? (I have to believe this is not the case.) In any case, is it more costly to use for (auto& it : vec) than for (auto it : vec)?

推荐答案

我想你将要花费太多的精力来模拟C ++ 11的功能。现在可以使用C ++ 98/03方法。

I think you are going into too much trouble to emulate C++11 functionality. You can use C++98/03 method for now. They will continue to work when you are able to use a C++11 compiler.

这样，你可以使用：

#if defined(CPP11_auto_type_inference) && defined(CPP11_range_based_for_loops)
  for (auto vit : args)
#else
  std::vector<std::string>::const_iterator viter, vend;
  for (vend=args.end(),viter=args.begin(); viter != vend; ++viter)
  {
     std::string vit = *viter;
#endif
     { // process arguments...
       std::cout << "Processing \"" << vit << '"' << std::endl;
       . . .
     } // end "process arguments" loop
#if defined(CPP11_auto_type_inference) && defined(CPP11_range_based_for_loops)  
#else
  }
#endif

如果你想仿效

  for (auto& vit : args)

您可以使用：

     std::string const& vit = *viter;

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