c++ - 错误 : no member function declared in class

Question

我的代码中不断出现以下错误:

(第 58 行)错误:没有在类“Person”中声明的“std::string Person::Modify_Person(Person)”成员函数在函数“int main()”中:

(第 113 行)错误:“Modify_Person”未在此范围内声明

代码如下:

#include <iostream>
#include <string>

using namespace std;

void PassByByValue(int num2){

  cout << "You are in PassByValue()" << endl;

  num2++;

}
class Person{
    int age;
    string name;
    int height;
    int weight;
public:

    Person(){

    }

    Person(string name){
        this->name=name;
    }

    string getName(){
    return this->name;
    }

    void setAge(int age){
    this->age=age;
    }


    void setName(string name){
    this->name=name;
    }

    void setHeight(int height){
    this->height=height;
    }

    void setWeight(int weight){
    this->weight=weight;
    }


    ~Person(){

    }

};



string Person::Modify_Person(Person example){

    example.getName()="Jessica";

    return example.getName();
}

void PassByRef(int& num3){

cout << "You are in PassByRef()" << endl;

num3=50;

cout << "inside PassByRef() pNum is: " <<num3<<endl;

}

int main()
{
   int num1;
   int* pNum;

    num1=3;
    *pNum=5;

    PassByByValue(num1);

    cout << "num1= " <<num1 <<endl;

    PassByRef(*pNum);

    cout << "outside PassByRef() in main() pNum is: " <<pNum<<endl;

    PassByByValue(*pNum);

    double* DblePtr;

    DblePtr= new double;

    *DblePtr=12.0;

    cout<< "DblePtr: "<< &DblePtr;

    delete[] DblePtr;

    cout<< "DblePtr: "<< &DblePtr;

    Person human;
    human.setName("Kate");
    human.setAge(27);
    human.setHeight(100);
    human.setWeight(100);

    Modify_Person(human);

    cout << "Modify_Person returns: " << Modify_Person(human) <<endl;

    cout << "name should be Jessica: " << human.getName() << endl;

    return 0;
}

Answer 1

您不能在 C++ 中的类外部声明成员函数。要解决此问题，请将相应的成员函数声明添加到您的类中:

class Person{
...
public:
string Modify_Person(Person);
};

然后你的代码就可以工作了。另外，一个建议:如果构造函数和析构函数为空，则不要定义它们；允许编译器为您生成它们。如果您打算通过这样做来禁用移动构造函数等，请编写 Person() = default; 让编译器生成默认实现。