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Hase Table - compiling error

This is a discussion on Hase Table - compiling error within the C Programming forums, part of the General Programming Boards category; Hi , Could you please help me whith this error? :86:16: error: invalid operands to binary == (have ‘IP_addres’ and ...

  1. #1
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    Feb 2013
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    Cool Hase Table - compiling error

    Hi ,
    Could you please help me whith this error?

    :86:16: error:
    invalid operands to binary == (have ‘IP_addres’ and ‘IP_addres’)

    Code:
    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    
    
    typedef struct
    {
      long l;
      union
      {
          unsigned int lo:16;
          unsigned int hi:16;
    
      }s;
    
    }IP_addres;
    
    typedef struct Node
    {
        IP_addres data;
        struct Node *next;
    
    } Node;
    
    
    
    Node *HashTable[10];
    
     //  Function //
    
    void create_hashtable(Node *HashTable[]) //  ‫‪create_hashtable Init‬‬
    {
        int index;
    
       for(index=0;index<10;index++)
        {
    
            HashTable[index]=NULL;
    
        }
    }
    
    
    
    Node* InsertNode(IP_addres Data)  //‫‪hashtable_insert‬‬
    {
    
        Node *first;
        Node *second;
        int index;
    
    
    
            first = (Node *) malloc(sizeof(Node));
            if (first== 0)
            {
                printf ( "out of memory \n");
                return(NULL);
            }
    
            if (HashTable[index] == NULL)
            {
                HashTable[index]=first;
                first->next=NULL;
                first->data=Data;
            }
            else
            {
                second=HashTable[index];
                first->next=second;
                first->data=Data;
            }
    
        return first;
    }
    
    void hashtable_remove(IP_addres Data)  //hashtable_remove
    {
            Node *head;
            Node *first=head;
            Node *second=head;
    
            if(head==NULL)
                printf("first element is empty\n");
    
            if(head->data==Data)
            {
                first=head->next;
                free(head);
    
            }
    
    
            while(first->next!=NULL)
         {
             second=first;
             first=first->next;
             if(first->data==Data)
             {
                 second->next=first->next;
                 free(second);
    
             }
    
    
         }
    
        }
    
    
    int hashtable_count(Node *node)
    {
        int i=0;
        while(node!=NULL)
        {
            node=node->next;
            i++;
        }
        printf("%d\n",i);
    
        return i;
    
    }
    
    void menu()
    {
        {
    
    
            puts("------------------------");
            puts("r. hashtable_remove");
            puts("i. InsertNode");
            puts("c. hashtable_count");
            puts("x. Exit");
    
        }
    }
    
    int main(void) {
    
        IP_addres IP;
        char c;
        Node *first;
        create_hashtable(HashTable);
    
        while(1)
        {
    
        start:        menu();
                printf("Enter IP Address:\n");
                    scanf("%x",&IP);
                c = getchar();
                switch(c)
                            {
                            case 'c': /* hashtable_count*/
                                hashtable_count( first);
                                goto start;
                                break;
                            case 'i': /* InsertNode*/
                                InsertNode(IP);
                                goto start;
                                break;
                            case  'r': /* hashtable_remove */
                                hashtable_remove(IP);
                                 goto start;
                                break;
    
                            case  'x': /* Exit */
                            break;
    
                            }
        }
    
        return 0;
    }

  2. #2
    Registered User
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    1,066
    Quote Originally Posted by ilans11il View Post
    :86:16: error:
    invalid operands to binary == (have ‘IP_addres’ and ‘IP_addres’)

    Code:
    if(head->data==Data)
    Both "head->data" and "Data" are structures and you can't compare them with the "==" operator.
    You can only compare its members with each other.

    Bye, Andreas

  3. #3
    and the hat of wrongness Salem's Avatar
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    > if(head->data==Data)
    You have to do this
    if(head->data.l == Data.l && head->data.s.lo == Data.s.lo && /* and all other members */ )

    C doesn't automatically know how to compare structs.

    Even in C++, you would have to overload == to make it work properly for a class/struct.

    And no, you can't use memcmp() either, before someone suggests you can.
    structs have padding and alignment, which means you have no control over the content of the padding space, and thus you can't tell whether there is a real difference or just a padding difference.
    iMalc likes this.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  4. #4
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    Feb 2013
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    Andreas , Salem

    Tank youuuuuuuuuu very much

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