Question

I was looking at a library a person has made for FaceBook in C++. The header file is this:

#ifndef __FACEBOOK_H__
#define __FACEBOOK_H__

/**
 * Facebook Class 
 * Joel Seligstein
 * Last mod: Aug 22, 2006
 *
 * This is the beginnings of a facebook class set and REST client.  Its not documented
 * yet nor nearly complete.  But this is a release to demonstrate its usefulness.  
 * Please email [e-mail] with suggestions or additions.
 *
 * TODO: Create classes/parsers for each request type
 * TODO: Linux URL launcher
 */

//uncomment to have verbose output turned on
//#define fb_debug 1

//define which platform you're compiling for
#define fb_windows 1
//#define fb_linux 1

#include <string>
#include <sstream>
#include <list>
using namespace std;

#ifdef fb_windows
#include <windows.h>
#endif

#include "curl/curl.h"
#include "xmlParser/xmlParser.h"
#include "md5.h"

class facebook
{
    public:
        //app/session vars
        string api_key;
        string secret;
        string token;
        string server;
        string session_key;
        string session_secret;
        string uid;
        bool has_session;

        facebook( string my_key, string my_secret, string my_server );
        bool authenticate( );
        bool request( string method, list<string> params, string *res );
        bool load_token( );
        void launch_login( string url );
        bool get_session( );
        void clean_up( );

    private:
        //curl info
        CURL *curl;
        CURLcode res;
        int call_id;

        //internal functions
        string get_signature( list<string> params );
        static string md5( string str );
        static string get_param_string( list<string> params, bool separate );
        static size_t write_callback( void *ptr, size_t size, size_t nmemb, void *userp );
};

#endif //__FACEBOOK_H__

Then inside the cpp file, my question is regarding this, the below is the constructor:

facebook::facebook( string my_key, string my_secret, string my_server )
{
    this->api_key = my_key;
    this->secret = my_secret;
    this->server = my_server;
    this->has_session = false;
    this->call_id = 0;
}

Why have they used the -> operator and not .?

I have a limited understanding that -> accesses properties and methods of the type directly in memory but I am confused, I would, through ignorance, expect to see:

facebook::facebook( string my_key, string my_secret, string my_server )
{
    this.api_key = my_key;
    this.secret = my_secret;
    this.server = my_server;
    this.has_session = false;
    this.call_id = 0;
}

All I want to know is the theory behind why -> is used over the dot notation.

---

UPDATE:
For anyone else in the same boat as me and learning C++. I have expanded on an example posted by a member in this question. I have also wrapped in initialization list for a member field.

#include "stdafx.h"
#include <iostream>
using namespace std;

class A {
private:
    int x;
public:
    A() : x(0){}
    int getX() const {return x;}
    void setX(int xx) {x += xx;}
};

int main()
{
    A a;

    a.setX(13);

    A *pa = &a;

    pa->setX(2);

    A b = a;

    b.setX(5);

    cout << "a" << a.getX() << endl;

    cout << "a*" << pa->getX() << endl;

    cout << "b" << b.getX() << endl;

    return 0;
}

Answer 1

this is a pointer to the current object i.e., inside methods (or constructor) of class A, this is of type A *.

(Note that, if the method is tagged as const, this is of type A const *.)

Hence the use of -> (designed only for pointers) and not . (designed only for class objects A or references to class objects A&).