解释错误：ISO C++ 禁止声明没有类型的“Personlist”

Explain the error: ISO C++ forbids declaration of `Personlist' with no type

提问by Ms01

I have a class which is going to handle an array of objects of another class I've created earlier (which works fine). The problem appears when I try to create an object of my List-class.

我有一个类将处理我之前创建的另一个类的对象数组（工作正常）。当我尝试创建 List 类的对象时出现问题。

This is the header of the list-class:

这是列表类的标题：

#ifndef personlistH
#define personlistH
#include "Person.h"
#include <iomanip>
#include <iostream>
#define SIZE 10

namespace std {

    class PersonList {
private:
    Person persons[SIZE];
    int arrnum;
    string filename;

public:
    Personlist();
    };
}
#endif

This is the main function:

这是主要功能：

#include <iostream>
#include "PersonList.h"

using namespace std;

int main() {

PersonList personlist;

return 0;   
}

The error my compiler is giving me is the following:

我的编译器给我的错误如下：

error: "27 \PersonList.h ISO C++ forbids declaration of `Personlist' with no type"

错误：“27 \PersonList.h ISO C++ 禁止声明没有类型的‘Personlist’”

I've searched for answers but as I'm quite new to C++ it's been a bit confusing and I haven't found any fitting yet. It would be great if you could explain this error for me.

我一直在寻找答案，但由于我对 C++ 很陌生，所以有点困惑，我还没有找到任何合适的答案。如果您能为我解释这个错误，那就太好了。

回答by RobH

You have the wrong capitalisation on your constructor declaration. You have Personlist();but need PersonList();. Because what you have isn't equal to the class name it is considered a function rather than a constructor, and a function needs a return type.

您的构造函数声明的大小写错误。你有Personlist();但需要PersonList();. 因为您拥有的不等于类名，所以它被视为函数而不是构造函数，并且函数需要返回类型。

回答by Alok Save

Do notadd your own types to the standard namespace(std), instead create your own namespace and define your class inside it.

不要将您自己的类型添加到标准命名空间（std），而是创建您自己的命名空间并在其中定义您的类。

//PersonList.h

//人员列表.h

namespace PersonNamespace 
{
    class PersonList 
    {
        //members here
    };
}

//Main.cpp

//主.cpp

using namespace PersonNamespace;

The actual error is that you made a typo in Personlistinstead of PersonList

实际的错误是你打错了Personlist而不是PersonList

回答by Mike Seymour

The error is because you got the capitalisation wrong when you declared the constructor; it should be PersonList()not Personlist().

错误是因为您在声明构造函数时弄错了大小写；应该PersonList()不是Personlist()。

Also, you should never declare your own classes in the stdnamespace; that's reserved for the standard library. You shoud make up your own namespace name, and put your things in that.

此外，永远不要在std命名空间中声明自己的类；这是为标准库保留的。您应该创建自己的命名空间名称，并将您的东西放入其中。