not a structure or union error

[burak aktas]

hi there i am trying to build a linked list from read a file operation. this code only adds the first node to the list. the problem is i am facing with "error: request for member 'head' in something not a structure or union" error. here is the code;

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "PR-ADT.h"
 
void add_Node(LIST** , NODE*);
LIST* create_list(void);
 
int main( void ) {
 
    LIST* list;
    NODE* student;
 
    list = create_list();
 
    FILE* myfile;
    char file_name[50];
    char sentence[200];
 
    printf("Enter the name of the file you want to create your list: ");
    gets(file_name);
    printf("\n");
 
    myfile = fopen(file_name,"r");
 
    while ( myfile == NULL ) {
 
        printf("File cannot be opened!!! Enter a new filename: ");
        gets(file_name);
        printf("\n");
 
        myfile = fopen(file_name,"r" );
    }
 
    while ( !feof(myfile) ) {
 
        fgets(sentence,200,myfile );
        puts(sentence);
    }
 
    rewind(myfile);
 
    student = (NODE*) malloc(sizeof(NODE));
 
    while ( !feof(myfile) ) {
 
        fscanf(myfile,"%s", &(student->first_name) );
        fscanf(myfile,"%s", &(student->last_name) );
        fscanf(myfile,"%s", &(student->email_addr) );
        fscanf(myfile,"%d", &(student->phone_num) );
        fscanf(myfile,"%s", &(student->address) );
        fscanf(myfile,"%s", &(student->city) );
        fscanf(myfile,"%d", &(student->zipcode) );
 
    }
 
    add_Node(&list,student);
 
    printf("%s", list->head->first_name );
 
    return 0;
}
 
void add_Node(LIST** list, NODE* student) {
 
    NODE* new_stu = student;
 
    new_stu = (NODE*) malloc(sizeof(NODE));
 
    if( !new_stu ) {
        printf("ERROR NOT ENOUGH MEMORY!!!\n");
        return;
    }
 
    else {
 
        new_stu->fn_next = NULL;
 
        if( *(list)->head == NULL ) {
 
            new_stu->fn_next = *(list)->head;
            *(list)->head = new_stu;
 
            printf("Adding operation is succesfull\n");
 
            *(list)->count++;
 
            return;
        }
    }
 
}
 

it gives the errors in add_Node function in all lines which include

*(list)

i try to add the first node only. so if i can manage to solve this problem i can continue on my work : ).

[Banfa]

Check your operator precedences, -> has a higher precedence than * and is applied first but list is not a pointer to a structure so the -> operator is not valid for it.

Using (list) does nothing and is a pointless waste of parentheses, you need to use parentheses to override the normal operator precedence by using (*list).

[burak aktas]

mate it worked. but i have a question this is my NODE and LIST structures;

typedef struct node {
 
    int birth_date;
    int zipcode;
    int phone_num;
    char first_name[50];
    char last_name[50];
    char city[50];
    char address[50];
    char email_addr[50];
 
    struct node* fn_next;
    struct node* ln_next;
    struct node* birdat_next;
 
} NODE;
 
typedef struct {
 
    int count;
    NODE* head;
    NODE* tail;
    NODE* current;
 
}LIST;

LIST* list

you say "list is not a pointer to a structure" . isn't this list includes 3 pointer to structures with names(head,tail ,current). could you explain why list is not pointer to a structure, i am confused : )_?

[Banfa]

in add_node void add_Node(LIST** list, NODE* student) list is declared as LIST **. So list is not a pointer to a structure, it is a pointer to a pointer to a structure. To declare a pointer to a structure you would need LIST* list (not that that would be right for your code.

If list is a pointer to a pointer to a structure then it needs to be dereferenced twice to get a structure. Both * and -> dereference a pointer, but * dereferences any pointer and -> dereferences a pointer to a structure so you need the * to be applied first because *list is a pointer to a structure.