C ++：is string.empty（）总是等效于string =="&quot ;?

问题描述

我可以假设给定

  std :: string str; 
 ... // do something to str 
  

以下语句总是为真吗？

 （str.empty（）==（str ==））
  
 
 
解决方案
 
回答
 
 
 
下面是 bits / basic_string.h 的相关实现， basic_string  
  / ** 
 *如果％string为空，则返回true。等同于* this ==。 
 * / 
 bool 
 empty（）const 
 {return this-> size（）== 0; } 
  
 
 
 
讨论
 
 
 
形式对 std :: string 是等效的，您可以 希望使用 .empty（） 
 
 
 
确实，评论说，如果您切换到使用 std :: wstring 而不是 std :: string   ==甚至不会编译，因为你不能比较 wchar_t  code> char 。但是，这与您的原始问题不直接相关，我99％确定您不会切换到 std :: wstring 。
 
Can I make an assumption that given
std::string str;
... // do something to str
Is the following statement is always true?
(str.empty() == (str == ""))
 解决方案 
Answer
Yes.  Here is the relevant implementation from bits/basic_string.h, the code for basic_string<_CharT, _Traits, _Alloc>:
  /**
   *  Returns true if the %string is empty.  Equivalent to *this == "".
   */
  bool
  empty() const
  { return this->size() == 0; }
Discussion
Even though the two forms are equivalent for std::string, you may wish to use .empty() because it is more general.
Indeed, J.F. Sebastian comments that if you switch to using std::wstring instead of std::string, then =="" won't even compile, because you can't compare a string of wchar_t with one of char.  This, however, is not directly relevant to your original question, and I am 99% sure you will not switch to std::wstring.
                        
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