c++返回null结构[复制]

This question already has an answer here:

这个问题已经有了答案:

Return a “NULL” object if search result not found 8 answers
如果搜索结果没有找到8个答案，返回一个“NULL”对象。

I have a struct like this

我有一个这样的结构。

struct AUTO{
   int weight;
   string name;
}

and I have a function that return a struct by passing name

我有一个函数，它通过名称返回struct。

AUTO autoByName(String name, AUTO a[], int ll)
{
   for(int i = 0; i < ll; i++)
   {
      if (name == a[i].name)
      {
         return a[i];
      }
   }

   // AND HERE ?????
}

but I don't know what return at the end of the function. Is there a null for struct ?

但我不知道函数结束时返回的是什么。结构是否为空?

1 个解决方案

#1

You have a lot of options:

你有很多选择:

Give AUTO a way to represent a "no-value". For example by making weight -1. Or by adding a flag to it. This is pretty ugly; I don't recommend it, even though it's somewhat common in practice.
给AUTO一种表示“无价值”的方法。举个例子，通过权重-1。或者添加一个标志。这是相当丑陋的;我不推荐它，尽管这在实践中很常见。
Return a (smart) pointer instead of value. This way you can return a nullptr in the case of error / no value. This is also ugly because it forces you to deal with pointers for not a very good reason.
返回一个(智能)指针，而不是值。这样，您可以在错误/没有值的情况下返回一个nullptr。这也很难看，因为它迫使你去处理指针，这不是一个很好的理由。
Return a separate value to indicate success. For example adding a bool &wasFound argument to the function.
返回一个单独的值来表示成功。例如，在函数中添加bool和wasfound参数。
Return boost::optional or std::pair<AUTO, bool> to accomplish pretty much the same thing, but all wrapped up in the return value. This is probably the cleanest. This is how std::map::find works, for example.
返回boost::可选或std::pair 完成几乎相同的事情，但都包在返回值中。这可能是最干净的。这就是std::map::find works，例如。 ,>
Throw an exception. It's possible that this is acceptable if callers don't try to find items that don't exist. In other words, if "not found" is just a return value then don't throw an exception. If "not found" is truly a program error condition, throwing an exception may actually make sense. If you're not sure, don't throw an exception.
抛出异常。如果调用者不尝试查找不存在的项，这是可以接受的。换句话说，如果“not found”只是一个返回值，那么不要抛出异常。如果“未找到”确实是一个程序错误条件，抛出异常可能是有意义的。如果你不确定，不要抛出异常。

I'd recommend #4, or in rarer cases #5.

我推荐#4，或者更少的案例#5。

#1