使用默认构造函数初始化变量 [英] Initializing a variable using default constructor

问题描述

我对c ++很新，我现在试图学习所有的基础知识，
我知道当默认构造函数被调用，但是当我尝试不同的语法，它不工作，像我预期的。 / p>

查看下面的代码：

  
 class b（）; 
 class c（NULL）; 
  

'class'是使用默认构造函数创建的类，
用于a和c工作得很好，但对于b，它只是不会将变量识别为类成员。

因为我看到b和c基本上是一样的，
谢谢！

解决方案

不要命名类 class



对于C ++，如果构造函数不带参数，则使用

  Foo a; //注意，如果你使用c ++ 11，你可以做Foo a {}; 
  

而不是：

  Foo b（）; 
  

这实际上是完全意外的事情，并声明一个名为 b 返回 Foo 实例。

对于 Foo c （null），它不会编译，因为没有接受参数的默认构造函数。

---

*它被称为最烦琐的解析，但我发现这是一个夸张。它可以肯定地抓住你的惊喜，但只是知道你可以声明一个函数原型，应该足以删除烦人的方面。

在其他字 int getMyInt（）; 显然是放在任何函数定义之外的函数原型。但是，由于也在函数定义内部的情况下， int getMyInt（）; 不会做任何通常会做的事情...这是定义一个返回整数的函数原型 getMyInt 。

I'm pretty new to c++, i'm now trying to learn all the basics, I know when default constructors are called, but when i tried different syntax it doesn't work like i expected.

Look at the following code:

class a;
class b();
class c(NULL);

'class' is a class i created with default constructor, for a and c everything works well, but for b it just won't recognize the variable as a class member.

As i see it b and c are basically the same, what's wrong than? Thanks!

解决方案

Don't name your class "class", as it is a reserved name.

As for C++, if the constructor takes no parameters, you instantiate it using

Foo a;   // note, if you are using c++11, you can do Foo a{};

As opposed to:

Foo b();

Which actually does something totally unexpected*, and declares a function named b that returns a Foo instance.

As for Foo c(null), it won't compile as there is no default constructor that takes an argument.

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* It is referred to as "the most vexing parse", though I find that to be an exaggeration. It can certainly catch you by surprise, but just knowing that you can declare a function prototype inside a function, should be enough to remove the "vexing" aspect.

In other words int getMyInt(); is obviously a function prototype when placed outside any function definitions. However, since this is also the case when inside a function definition, int getMyInt(); doesn't do anything it wouldn't normally do... which is to define a function prototype getMyInt that returns an integer.

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