malloc

This is a discussion on malloc within the C Programming forums, part of the General Programming Boards category; Hey guys im loading some data from a file into memory using the structs.. i need to allocate some memory ...

  1. #1
    Musicman - Canora
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    malloc

    Hey guys im loading some data from a file into memory using the structs.. i need to allocate some memory for it using malloc but im unsure which variables i need to use to allocate memory for the structs.

    could someone also explain a little more about the structs


    Code:
    typedef struct category* CategoryTypePtr;
    typedef struct item* ItemTypePtr;
    
    /* Structure definitions. */
    typedef struct price
    {
       unsigned dollars;
       unsigned cents;
    } PriceType;
    
    typedef struct item
    {
       char itemID[ID_LEN + 1];
       char itemName[MAX_NAME_LEN + 1];
       PriceType prices[NUM_PRICES];
       char itemDescription[MAX_DESC_LEN];
       ItemTypePtr nextItem;
    } ItemType;
    
    typedef struct category
    {
       char categoryID[ID_LEN + 1];
       char categoryName[MAX_NAME_LEN + 1];
       char drinkType;      /* (H)ot or (C)old. */
       char categoryDescription[MAX_DESC_LEN];
       CategoryTypePtr nextCategory;
       ItemTypePtr headItem;
       unsigned numItems;
    } CategoryType;
    
    typedef struct gjc
    {
       CategoryTypePtr headCategory;
       unsigned numCategories;
    } GJCType;

  2. #2
    Registered User 00Sven's Avatar
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    You need to malloc() memory for each structure so make a pointer.
    Code:
    int main(){
         GJCType *name;
         name = malloc(sizeof(GJCType));
         name -> headCategory = malloc( sizeof(CategoryType) );
         name -> headCategory -> headItem=malloc( sizeof(ItemType) );
         name -> headCategory -> nextCategory = malloc( sizeof(CategoryType) );
         name -> headCategory -> headItem -> nextItem = malloc( sizeof(ItemType) );
    }
    And so on...
    ~Sven
    Last edited by 00Sven; 04-19-2006 at 09:23 AM.
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  3. #3
    Just kidding.... fnoyan's Avatar
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    And don't forget to make type casting!Because malloc() return a *void

  4. #4
    Sys.os_type="Unix";;
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    Quote Originally Posted by fnoyan
    And don't forget to make type casting!Because malloc() return a *void
    What are you referring to? Casting the return value of malloc?
    C does type coercian from void to any other type automatically so casting malloc only has the potential of evil side-effects.

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