`List x;`和'List x（）`之间有什么区别 [英] Is there any difference between `List x;` and `List x()`

问题描述

标题来自着名网站 C ++

作者声称以下两个代码示例之间有区别。

假设List是某个类的名称。然后函数f（）声明一个名为x的局部List对象：

  void f b $ b {
 List x; // Local类名为x（List类）
 ... 
} 
  

< blockquote>

但是函数g（）声明了一个函数x（），返回一个List：

  void g（）
 {
 List x（）; //函数命名为x（返回一个List）
 ... 
} 
  

但是使用第二个变量是真的错了吗？

如果它真的是一个声明，不会编译器抱怨说你不能在函数中声明一个函数

解决方案

如果它真的是一个声明不会编译器抱怨你不能声明函数内的函数。

当然不是。

这是最令人烦恼的解析，因此您可以可以声明函数。事实上，它代表编译器处理一个错误

  List x（）; 
  

作为变量声明。

但是使用第二个变量真的错了吗？

如果你想要一个变量，如果你想声明一个函数... kinda是的。你可以，但通常你会在函数范围之外。

The title comes from the famous site C++ FAQ by Marshall Cline.

The author claims that there is a difference between the following two code examples.

Suppose that List is the name of some class. Then function f() declares a local List object called x:

void f()
{
    List x;     // Local object named x (of class List)
    ...
}

But function g() declares a function called x() that returns a List:

void g()
{
    List x();   // Function named x (that returns a List)
    ...
}

But is it really wrong to use the second variant?

And if it really is a declaration wouldn't the compiler complain that you cannot declare a function within a function?

解决方案

And if it really is a declaration wouldn't the compiler complain that you cannot declare a function within a function.

Of course not. Because you can declare a function withing a function.

This is called most vexing parse and it's well documented. In fact, it would be an error on behalf of the compiler to treat

List x();

as a variable declaration.

But is it really wrong to use the second variant?

If you want a variable, then yes. If you want to declare a function... kinda yes. You can, but usually you'd do it outside of a function scope.

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