typedef question

This is a discussion on typedef question within the C Programming forums, part of the General Programming Boards category; can I have two typedef with the same name but different things inside of it?...

  1. #1
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    typedef question

    can I have two typedef with the same name but different things inside of it?

  2. #2
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by -EquinoX- View Post
    can I have two typedef with the same name but different things inside of it?
    You cannot have two typedefs with the same name, period.

  3. #3
    and the hat of sweating
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    Sure, as long as they aren't in the same file and never get #included together.
    Why would you want to? That would be very confusing.

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    hmm.. can I cast a typedef? it's basically just a pointer right?

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    Quote Originally Posted by -EquinoX- View Post
    hmm.. can I cast a typedef? it's basically just a pointer right?
    No. A typedef names a type. It has nothing to do with pointers or any other kind of variable. What are you trying to do?

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    so I have this:

    Code:
    struct node_t{
      char* word;
      bla.. bla.. bla
    }
    
    typedef struct node_t Words;
    when I call LinkedListConstruct it returns Words*, when I call HashTableConstruct I want it to return a similar thing too.. Words*, but my hashtable function returns a HashTable* which is a different kind of struct from Words*

  7. #7
    and the hat of sweating
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    Quote Originally Posted by -EquinoX- View Post
    so I have this:

    Code:
    struct node_t{
      char* word;
      bla.. bla.. bla
    }
    
    typedef struct node_t Words;
    when I call LinkedListConstruct it returns Words*, when I call HashTableConstruct I want it to return a similar thing too.. Words*, but my hashtable function returns a HashTable* which is a different kind of struct from Words*
    So why not call one LinkedListNode and the other HashTableNode?

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    I can't because I have a file that I can't change and that file does:

    Words* f = DictionaryConstruct(some argument here); <== I can't change this!

    and inside dictionary construct I have two types of construct, one is a hashtable construct and a bst construct.. which both returns a different type of struct.. and on the other hand I need to return a pointer to a struct called *Words

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    I mean when constructing a linked list and a bst, you got two different things going on at the same time:

    in a struct of a linked list I have the next node (which is basically another struct inside a struct) I have the data itself. in a bst in the struct I have a left and right tree which is another struct inside a struct and the data

  10. #10
    and the Hat of Guessing tabstop's Avatar
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    So what you're really asking is "can I make a function return two different things, depending on the phase of the moon and other unrelated things?" The answer is no -- DictionaryConstruct must always return the same type; it should never return sometimes a hashtable and sometimes a search tree. Pick one.

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    hmm.. so I can only return one? okay then, I'll have to figure out another way through this then.. by the way if I am implementing a hashtable, how can I get all the elements in that hash table if I don't know the key? is there a way to traverse a hash table?

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    hmm..let me explain my situation here more clearly:

    so I have a code optimization assignment to be done. The program basically just takes two files,
    first it stores the list of words in a data structure unsortedly in a hash table. Second it takes the second file, which is also a list of words. Before storing the second list of words into a binary tree I want to check first if that word exists in the first file, by checking the hash table. If it does exist then I put that word in a binary tree. In other words, two similar words that exists on both files are put inside a binary tree.

    The problem is I have this code that I can't change or do anything to it:

    Words* fd = Construct(..)

    Words is just a pointer to a struct evertime it constructs that list of words file into a linked list (the current implementation is a linked list). But my HashTable returns a pointer to a struct which supports a hash table, a struct with key and values inside and my BinaryTree returns a pointer to a struct which is a binary tree struct/node that has a left and right subtree.

  13. #13
    and the Hat of Guessing tabstop's Avatar
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    On the assumption your hash table is an array of linked lists, you can walk each linked list in order.

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    yes, my hash table is an array of linked list.. so I have to check each array slot it there's a data in that linked list? I guess this wouldn't be so efficient right

    is there a way to iterate over a hash table and get the data one by one in a sorted way?

  15. #15
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by -EquinoX- View Post
    yes, my hash table is an array of linked list.. so I have to check each array slot it there's a data in that linked list? I guess this wouldn't be so efficient right

    is there a way to iterate over a hash table and get the data one by one in a sorted way?
    Unless your array of lists is somehow exponentially larger than it needs to be, traversal of a hash table is just as efficient of traversal of anything else; most every traversal is O(n) since you have to visit every item once.

    Unless your hashing mechanism and list-inserting mechanism are very carefully designed, traversal of a hash table will not be in sorted order.

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