Thread: Question regarding pointers

Hey guys,

I have programmed a tree structure with the help of my C++ book and was wondering about the usage of double pointers by the author.

Here's the code:

Code:

#include <iostream>
#include <malloc.h>
#include <string>
using namespace std;

struct link_str{
    string *pbegriff;
    link_str *left;
    link_str *right;

};

void eintragen(link_str **pstart, string s1){
    
    link_str *pliste;
    pliste = *pstart;

    //First Case
    if(pliste == NULL){
        pliste = (link_str *)malloc(sizeof(link_str));

        

        pliste->pbegriff = new string(s1);
        pliste->left = NULL;
        pliste->right = NULL;

        *pstart = pliste; 
        return;
    }
    while(pliste != NULL){
        if(s1 <= *(pliste->pbegriff)){
            if(pliste->left != NULL){
                pliste = pliste->left;
            } else {
            pliste->left =(link_str *)malloc(sizeof(link_str));
            pliste = pliste->left; 

                //Datensatz
            pliste->pbegriff = new string(s1);
            pliste->left = NULL;
            pliste->right = NULL;


            pliste = NULL; 
            }
        } else {
            if(pliste->right != NULL){
                pliste = pliste->right; 
            } else {
                pliste->right =(link_str *)malloc(sizeof(link_str));
                pliste = pliste->right; 

                
                pliste->pbegriff = new string(s1);
                pliste->left = NULL;
                pliste->right = NULL;


                pliste = NULL; //Schleife zu Ende
            }
        }
    }//while(pliste != NULL)


}//void eintragen(link_str **pstart, string s1)

void ausgabe(link_str *pliste){

    if (pliste == NULL) return;
    ausgabe(pliste->left); //Rekursion
    cout << "Sorted:  " << * (pliste->pbegriff) << endl;
    ausgabe(pliste->right);//Rekursion
}

void freigeben(link_str *pliste){
    if (pliste == NULL) return;
    freigeben(pliste->left);
    freigeben(pliste->right);
    delete(pliste->pbegriff);
    free(pliste);
}

int main() {

    

    

    link_str *pstart = NULL; 

    string s1;

    //Filling the list
    do {
        getline(cin, s1,'\n');
        if(s1 != "QUIT"){
            eintragen(&pstart,s1);
        }

    }while(s1 != "QUIT");

    //output of the list

    ausgabe(pstart);

    //Free the list

    freigeben(pstart);
    pstart = NULL;



    return 0;
}

My question:

1.Instead of writing eintragen(link_str **pstart,string s1) in line 13 which gets the value (&pstart, s1) in line 98, wouldn't it be enough if I just delete one & and one * and getting this:

eintragen(link_str *pstart,string s1) which just gets the value (pstart,s1).
Unfortunately the code doesn't work anymore, if I put it like that.

(Also, you have to change line 16 and 28 from *pstart to just pstart, as you only have to dereference once.)