基于范围的for循环中未命名的循环变量？ [英] Unnamed loop variable in range-based for loop?

问题描述

有没有什么方法不能在基于范围的for循环中使用循环变量，但也避免编译器对它未使用的警告？

，我想做一些像下面的事情。我有治疗警告作为错误启用，我宁愿不做一个黑客，强迫变量被使用无意义地提到它在某个地方。

  size_t getSize（const std :: forward_list& list）
 {
 size_t count = 0; 
 for（auto&：list）//编译错误，但是如果我在这里做auto& i，MSVC 
 //（合理地）抱怨我是未使用
 {
 ++ count; 
} 
 return count; 
} 
  

我知道还有其他方法可以做到这一点，我需要使用基于范围的for循环。

解决方案

你可以明确地声明变量在循环体：

  ptrdiff_t size（std :: forward_list const& list）
 {
 ptrdiff_t count = 0; 
 for（auto& dummy：list）
 {
（void）dummy; struct dummy; //如果你想要在一个宏包装。 
 //这里每个人都包括编译器知道虚拟没有使用，不能使用。 
 
 ++ count; 
} 
 return count; 
} 
  

然而，上述情况远比简单使用普通的

更不用说简单地调用 size p>

Is there any way to not "use" the loop variable in a range-based for loop, but also avoid compiler warnings about it being unused?

For context, I'm trying to do something like the following. I have "treat warnings as errors" enabled, and I'd rather not do a hack like forcing the variable to be "used" by pointlessly mentioning it somewhere.

size_t getSize(const std::forward_list &list)
{
  size_t count = 0;
  for (auto & : list) // compile error, but if i do "auto &i" here, MSVC
                      // complains (reasonably) that i is unused
  {
    ++count;
  }
  return count;
}

I know there are other ways to do this, but let's say for argument's sake that I need to use a range-based for loop.

解决方案

You can always state explicitly that the variable is guaranteed unused in the loop body:

ptrdiff_t size( std::forward_list const& list )
{
    ptrdiff_t count = 0;
    for( auto& dummy : list ) 
    {
        (void) dummy; struct dummy;    // Wrap this in a macro if you want.
        // Here everybody including compiler knows that dummy isn't used and can't be used.

        ++count;
    }
    return count;
}

The above is however much less clear than simply using an ordinary for-loop.

Not to mention simply calling size.

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