可以在分配期间在C ++中给出类的定义，这在Java中是允许的 [英] Is it possible to give a definition of a class in C++ during allocation, as is allowed in java

问题描述

或者只需输入

即可执行

  class A {
 public：
 virtual void foo（）= 0; 
}; 
 
 B类{
 public：
 A * a; 
 b（）{
 a = new A（）{void foo（）{printf（hello）;} 
} 
} 
  
没有，C ++没有类似Java的匿名类。
 
 
 
您可以定义本地类，例如：
  B {
 public：
 A * a; 
 b（）{
 struct my_little_class：public A {
 void foo（）{printf（hello）;} 
}; 
 a = new my_little_class（）; 
} 
}; 
  
或者只是一个嵌套类：
  class B {
 private：
 struct my_little_class：public A {
 void foo（）{printf（hello）;} 
 }; 
 
 public：
 A * a; 
 
 b（）{
 a = new my_little_class（）; 
} 
}; 
  
在C ++ 03中，本地类有一些限制（例如，它们不能使用作为模板参数）在C ++ 11中提升。
 
 
 
在Java中，匿名类有时用于做其他语言做匿名函数，当您创建 Runnable 的匿名实现。 C ++ 11有匿名函数（也称为lambdas），所以如果这是你想要实现的，可以是一个选项。
 
Or simply put

can I do some thing like
class A {
public:
  virtual void foo() = 0;
};

class B {
  public:
    A *a;
    b(){
       a = new A() { void foo() {printf("hello");}
    }
};

解决方案
No, C++ doesn't have anonymous classes like Java's.

You can define local classes, like this:
class B {
  public:
    A *a;
    b(){
       struct my_little_class : public A {
           void foo() {printf("hello");}
       };
       a = new my_little_class();
    }
};
Or maybe just a nested class:
class B {
  private:
    struct my_little_class : public A {
        void foo() {printf("hello");}
    };

  public:
    A *a;

    b(){
       a = new my_little_class();
    }
};
In C++03, local classes have some limitations (for example, they can't be used as template parameters) that were lifted in C++11.

In Java, anonymous classes are sometimes used to do what other languages do with anonymous functions like, for example, when you create an anonymous implementation of Runnable. C++11 has anonymous functions (also known as lambdas), so that could be an option if this is what you're trying to achieve.

                        
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