C++ 如何在类中声明结构？
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How do I declare a struct within a class?
提问by haddad
I want to declare a struct within a class which is private and I want to give a character value to a variable in the same struct, but I can't initialize it or cin it:
我想在一个私有的类中声明一个结构，我想给同一个结构中的一个变量一个字符值，但我不能初始化它或cin它：
class puple
{
private:
struct p
{
char name[25];
int grade;
};
public:
puple(){};
void setme()
{
this->p::grade=99;
this->p::name[25]='g'; //here is the problem
}
void printme()
{
cout<<"Name: "<<this->p::name<<endl;
cout<<"Grade: "<<this->p::grade<<endl;
}
};
void main()
{
puple pu1;
pu1.setme();
pu1.printme();
}
回答by Doug T.
You've describe a type called "p" which is a struct. There is yet no thing of type p around. Therefore your
您已经描述了一种名为“p”的类型，它是一个结构体。周围还没有 p 类型的东西。因此你的
p->...
calls make no sense.
打电话没有意义。
Try declaring
尝试声明
p pInstance;
in your class and using it, ie:
在你的课堂上并使用它，即：
void setme()
{
this->pInstance.grade=99;
this->pInstance.name[25]='g'; //here is the problem
}
Note even with this your assignment to name[25] will fail as the allowed indices for that array are 0 up to 24 (totalling 25 elements).
请注意，即使这样，您对 name[25] 的分配也会失败，因为该数组的允许索引为 0 到 24（总共 25 个元素）。
回答by jkerian
You have two serious problems here
你这里有两个严重的问题
struct p
{
char name[25];
int grade;
};
This defines a struct type, named p. I think what you wanted to do was
这定义了一个名为 p的结构体类型。我想你想做的是
struct
{
char name[25];
int grade;
} p;
This will declare a struct, named p, with the name and grade member variables.
这将声明一个名为 p的struct，其中包含 name 和 grade 成员变量。
Your second serious problem is that you assign:
您的第二个严重问题是您分配了：
this->p::name[25]='g'; //here is the problem
This assigns 'g' to the 26th element of the array name. (arrays are 0-indexed)
这将 'g' 分配给数组名称的第 26 个元素。（数组是 0 索引的）
回答by THX-1138
isn't it
是不是
struct { ... } p; // variable of struct-type definition.
not
不是
struct p { ... }; // type 'struct p' definition.
?
?
回答by Will Bickford
Place the struct definition outside of the class using a typedef. By having the struct defined in your .cpp file it will not be visible outside of your class.
使用 typedef 将 struct 定义放在类之外。通过在您的 .cpp 文件中定义结构，它在您的类之外将不可见。
#include <iostream>
typedef struct _foo
{
int a;
} foo;
class bar
{
public:
void setA(int newa);
int getA();
private:
foo myfoo;
};
void bar::setA(int newa)
{
myfoo.a = newa;
}
int bar::getA()
{
return myfoo.a;
}
using namespace std;
int main()
{
bar mybar;
mybar.setA(17);
cout << mybar.getA() << endl;
return 0;
}
