Is it possible to access a class member in a global function? - c++

Question

Though I'm sure this is a common issue, I haven't been able to find a thread on this. The closest I found was here, but it didn't ultimately seem to be asking the same thing.
I'm fairly new to C++, so I may just be doing something dumb.
Say I have the following Person class setup (Sorry for all of the code. I'm not sure exactly where the problem is--if this is even possible--so I'm including everything.):
person.h
#ifndef PERSON_H
#define PERSON_H
#include <string>
using std::string;
class Person {
public:
Person();
Person(string name);
~Person();
string name;
private:
};
#endif
person.cpp
#include "person.h"
Person::Person() {
}
Person::Person(string name) {
this->name = name;
}
Person::~Person() {
}
Then I want a global function that will change the name property of a given person:
globals.h
#ifndef GLOBALS_H
#define GLOBALS_H
#include <string>
using std::string;
class Person; // forward declaring
void changeName(Person* person, string name);
#endif
globals.cpp
#include "globals.h"
void changeName(Person* &person, string name) {
person->name = name;
}
When I try to compile I get "incomplete class" and "forward declaration" errors (I can provide if necessary). Am I doing something wrong, or would I have to do this using a class member function (e.g. Person::changeName(.....))?
Thank you for the help.

Answer 1

Your globals.cpp file lacks the necessary #include "person.h".
There are some other problems, too:
void changeName(Person* person, string name);
This should probably be:
void changeName(Person& person, string name);
Unless you want to make it possible to call the function with nullptr.
void changeName(Person* &person, string name) {
person->name = name;
}
Should be:
void changeName(Person& person, string name) {
person.name = name;
}
Then there's this:
Person::Person(string name) {
this->name = name;
}
You should use an initialisation list instead:
Person::Person(string name) : name(name) {}
And I'm not sure if you are aware of the possibility of passing std::string via const&. It used to be the guideline for passing strings, until C++11 came along and created ongoing discussions about best practices for passing big objects.

Answer 2

For a start the following:
Person(string name);
should be
Person(const string& name);
For performance
And string name should be in the private bit,
Also then signature for
void changeName(Person* person, string name);
in the header differs from the code in the .cpp file
i.e.
void changeName(Person* &person, string name) {
Also put in the #include as stated by the other person