[C++] C++在类的内部声明函数，在类的外部定义函数

//在类的外部定义内部函数
#include<iostream>
#include<vector>
#include<string>
using namespace std;
struct user {
string id(string id="") {
if (id.size()) {
this->user_id = id;
}
return this->user_id;
}
string user_id;
string password(string password="") {
if (password.size()) {
this->user_password = password;
}
return this->user_password;
}
string user_password;
int out();
};
int user::out(){
cout << "这是一个在类内部声明在类外部定义的函数\n";
return 0;
};
int main(void) {
struct user user;
user.user_id = "gaowanlu";
user.user_password = "133466377";
user.password("1234567890");//修改密码
cout << user.id() << endl;
cout << user.password() << endl;
user.out();
return 0;
}