Thread: Problems with recursive structure

Hello,

I'm trying to understand the logic of recursive structures (or is "linked list" much proper term?) and I have a problem with following code:

Code:

#include <stdio.h>
#include <stdlib.h>


struct person
    {
    const char *first_name;
    const char *last_name;
    int age;
    struct person *next;
    };

typedef struct person PERSON;


void add_new_person(PERSON **p_obj, const char *first_name, const char *last_name, int age)
    {
    PERSON *p = (PERSON *)malloc(sizeof(PERSON));
    p = *p_obj;

    if(p->next != NULL)
        p = p->next;

    p->first_name = first_name;
    p->last_name = last_name;
    p->age = age;

    p->next = (PERSON *)malloc(sizeof(PERSON));

    return;
    }


void show_persons(PERSON **p_obj)
    {
    PERSON *p = (PERSON *)malloc(sizeof(PERSON));
    p = *p_obj;

    if(p != NULL)
        {
        while(p->next != NULL)
            {
            printf("%s %s (age: %d years)\n"
                , p->first_name
                , p->last_name
                , p->age
                );

            p = p->next;
            }
        }

    return;
    }


int main(void)
    {
    PERSON *nice_person = (PERSON *)malloc(sizeof(PERSON));

    add_new_person(&nice_person, "Donald", "Duck", 122);
    add_new_person(&nice_person, "Jack", "Sparrows", 32);
    add_new_person(&nice_person, "Bruce", "Wayne", 40);
    add_new_person(&nice_person, "Gregory", "House", 55);
    add_new_person(&nice_person, "Luke", "Skywalker", 20);
    add_new_person(&nice_person, "Hannibal", "Lecter", 65);

    show_persons(&nice_person);

    return 0;
    }

I was hoping it prints out all six of the names, but the actual outpot is:

Code:

Donald Duck (age: 122 years)
Hannibal Lecter (age: 65 years)

(the first and the last item from the list).

I can't figure out what am I doing wrong here.

I can not see why the malloc in start of main function is needed.I would suggest you to just declare the pointer and set it to NULL.

add_new_person adds a person (a node of the list in other words) in the end of the list...So maybe you should

Code:

p->next=NULL;

as the last node has never a next one

Thanks for the advices given so far. I'll try to follow at least most of them.

Just a brief note considering this line:

Code:

PERSON *p = (PERSON *)malloc(sizeof(PERSON));

Since I try to make my code compatible with both C and C++ compilers, casting the return value of malloc is actually needed.

Originally Posted by heinz55

Since I try to make my code compatible with both C and C++ compilers, casting the return value of malloc is actually needed.

Well in C++ actually you would use the keyword new instead of malloc

Originally Posted by std10093

Well in C++ actually you would use the keyword new instead of malloc

You are correct, but traditional C does not support the "new" keyword.

Originally Posted by heinz55

You are correct, but traditional C does not support the "new" keyword.

You are correct too in this case

Originally Posted by heinz55

... I try to make my code compatible with both C and C++ compilers ...

Then you get something that is neither C nor C++.
Happy coding!

Originally Posted by qny

Then you get something that is neither C nor C++.
Happy coding!

He is correct too

Originally Posted by qny

Then you get something that is neither C nor C++.
Happy coding!

Don't be harsh about it. You know if you want a half-monkey and half-human, you just get one of each species, cut them in half, and stitch one half from each species, together -- Bingo!

That's just common sense.

Originally Posted by qny

Then you get something that is neither C nor C++.
Happy coding!

I'm just trying to write C code that can be compiled with C++ compilers as well. Simple as that.
But if I write C++ then I try to keep it pure C++.