Problem storing in char pointer

This is a discussion on Problem storing in char pointer within the C Programming forums, part of the General Programming Boards category; Hello, I'm new to C, and have been messing around with pointers. I have a program that creates a "movienode' ...

  1. #1
    Registered User
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    May 2008
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    2

    Problem storing in char pointer

    Hello,

    I'm new to C, and have been messing around with pointers. I have a program that creates a "movienode' struct that stores two ints and a char pointer (string).

    When creating nodes in the program, the string are stored successfully in nodes I create. However, in my addMovie function I am apparently not storing the char correctly because upon calling printQueue I see that instead of a title I get giberish (example: �'� �)

    I originally had *title instead of title[40] in addMovie, and had scanf save to &title instead of title... but printQueue would segfault.

    If anyone could help me, I'd appreciate it.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <string.h>
    struct movienode {
    char *title;
    int year;
    int id;
    struct movienode *next;
    };
    //global head
    struct movienode *movie = NULL;
    //define
    void printQueue (struct movienode *);
    
    int main (void) {
    struct movienode *m1 = (struct movienode *) malloc(sizeof(struct movienode));
    struct movienode *m2 = (struct movienode *) malloc(sizeof(struct movienode));
    movie = m1;
    movie->year = 1985;
    movie->id = 1582;
    movie->title = "Movie1";
    movie->next = m2;
    m2->year = 1955;
    m2->title = "Movie2";
    m2->id = 1583;
    menu();
    return 0;
    }
    void printQueue (struct movienode * h) {
    while (h != 0)
    {
    printf("Movie: &#37;s Year: %d ID: %d",h->title, h->year, h->id);
    printf("\n");
    h = h->next;
    }
    }
    void addMovie (struct movienode * h)
    {
    struct movienode *temp = (struct movienode *) malloc(sizeof(struct movienode));
    char title[32];
    int year;
    int id;
    printf("\nEnter movie title: ");
    scanf("%s", title);
    printf("\nEnter movie year: ");
    scanf("%d", &year);
    printf("\nEnter movie id: ");
    scanf("%d", &id);
    temp->id = id;
    temp->year = year;
    temp->title = title;
    temp->next = h;
    movie = temp;
    }
    int findMovie (struct movienode * h)
    {
        int id;
        int curid;
        printf("Enter movie ID to search for: ");
        scanf("%d", &id);
        while (h != 0)
        {
                if (h->id == id)
                {
                    printf("Movie: %s Year: %d ID: %d", h->title,h->year,h->id);
                    return 1;
                }
                else
                    h=h->next;
        }
        printf("Not found.");
        return 0;
    }
    int delMovie (struct movienode * h)
    {
        int id;
        printf("Enter movie ID to delete: ");
        scanf("%d", &id);
        if (h->id == id)
        {
            movie = h->next;
            free(h);
            return 1;
        }
        while (h != 0)
        {
            if (h->next->id == id)
            {
                h->next = h->next->next;
                free(h->next);
                return 1;
            }
            else
                h=h->next;
             
        }
        printf("Not found");
        return 0;
    }
    void menu(void)
    {
        int opt;
        while (opt != 0)
        {
            printf("\n\nMenu\n\n\n");
            printf("1. Print Movies\n");
            printf("2. Add Movie\n");
            printf("3. Del Movie\n");
            printf("4. Search Movies\n");
            printf("0. Exit");
            printf("\n\nEnter option: \n");
            scanf("%d", &opt);
            if (opt == 1)
                printQueue(movie);
            else if (opt == 2)
                addMovie(movie);
            else if (opt == 3)
                delMovie(movie);
            else if (opt == 4)
                findMovie(movie);
    }
    }
    Last edited by Termina; 05-02-2008 at 08:04 PM.

  2. #2
    Deathray Engineer MacGyver's Avatar
    Join Date
    Mar 2007
    Posts
    3,211
    One problem I have spotted right away is this from addMovie():

    Code:
    temp->title = title;
    title is actually a local char array. It will be destroyed around the time control returns from the function (Note: This is not entirely true, but to get into any more of a detailed discussion would probably not be beneficial.).

    temp->title will simply point to this local variable. This is bad. Once something wrecks the memory in title some time after the function returns, temp->title is also wrecked because temp->title simply points to title. What you need to do is malloc() space for temp->title to hold strlen(title) +1 and then strcpy(temp->title, title). Remember to free() the malloc()'ed memory that you allocate for temp->title, however.

  3. #3
    Registered User
    Join Date
    May 2008
    Posts
    2
    Thank you for the quick reply!

    That solved my problem. I wish my professor had gone over strcpy.

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