访问类中的结构的成员 [英] accessing member of structure within a class

问题描述

我有一个.hpp和.cpp文件。我想访问一个类中的结构中的变量，恰好在.hpp文件的头文件中，在.cpp文件中。

在.hpp中，我有

  class foo {
 
 public：
 struct packet {
 int x; 
 u_int y; 
}; 
 
}; 
 
 foo（const char * name）
：m_name（name）{} 
  

在.cpp中我做了：

  foo * foo_1 =& foo; 
 printf（x的值是：％d，foo_1-> packet.x）; 
 printf（y的值是：％u，foo_1-> packet.y）; 
  

这样做时，我收到以下错误：

  code_1.cpp：117：错误：期望的主表达式';'令牌
 code_1.cpp：118：错误：无效的使用'struct foo :: packet '
 code_1.cpp：119：错误：无效使用'struct foo :: packet'
 make：*** [code_1]错误1 
  pre> 
 
 
我的目标是获取cpp文件中x和y的值。 
 
 
 
感谢。
解决方案
您需要在类foo 中  c>类型 foo :: packet  / p> 
 
 
  class foo {
 
 public：
 struct packet {
 int x; 
 u_int y; 
}; 
 
 packet my_packet; //<  -  THIS 
}; 
  
在您的.cpp中，您应该执行：
  foo * foo_1 =& foo; 
 printf（x的值是：％d，foo_1-> my_packet.x）; 
 printf（y的值为：％u，foo_1-> my_packet.y）; 
  
您必须记住，即使包在 foo 中，它不包括在 foo 中作为成员对象。它只是一个封装在另一个类中的类。对于要使用的类，你必须有它的对象（一个类也可以使用没有它的对象，但是，好...）。
 
I have an .hpp and .cpp file. I want to access the variable in the structure within a class which happens to be in the header .hpp file, in the .cpp file. 

In .hpp, I have
class foo{

public:
       struct packet{
         int x;
         u_int y;
      };

};

 foo(const char*name)
:m_name(name){}
In .cpp I did:
foo *foo_1 = &foo;
printf("The value of x is : %d",foo_1->packet.x);
printf ("The value of y is : %u", foo_1->packet.y);
On doing this I receive the following error:
code_1.cpp:117: error: expected primary-expression before ‘;’ token
code_1.cpp:118: error: invalid use of ‘struct foo::packet’
code_1.cpp:119: error: invalid use of ‘struct foo::packet’
make: *** [code_1] Error 1
My objective is to get the values of x and y in the cpp file. Any suggestion/idea will be really appreciated.

Thanks.
解决方案
You need a member object of type foo::packet in class foo.
class foo{

public:
      struct packet{
         int x;
         u_int y;
      };

      packet my_packet;   // <- THIS
};
In your .cpp, you should do:
foo *foo_1 = &foo;
printf("The value of x is : %d",foo_1->my_packet.x);
printf ("The value of y is : %u", foo_1->my_packet.y);
You must remember that even though packet is inside foo, it is not included in foo as a member object. It is just a class enclosed inside another class. And for a class to be used, you must have objects of it (a class can also be used without having objects of it, but, well...).

                        
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