Struct array malloc and realloc

This is a discussion on Struct array malloc and realloc within the C Programming forums, part of the General Programming Boards category; I'm trying to get a struct to malloc (one time its size) this is the code: Code: #include <stdio.h> #include ...

  1. #1
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    Feb 2008
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    Question Struct array malloc and realloc

    I'm trying to get a struct to malloc (one time its size) this is the code:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    #define MAX_STRING 128
    
    typedef char String[MAX_STRING];
    
    typedef struct {
            String Name;
            double Size;
    } ArrayType;
    
    typedef ArrayType Array[];
    
    int main(void) {
    
    Array = malloc(sizeof(*Array));
    
    }
    isn't this the right way?
    Also, i cant figure out how to realloc the array.
    I would really appreciate any help.
    Last edited by pseudonoma; 03-01-2008 at 05:59 PM.

  2. #2
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    What are you doing with that last typedef?

    What are you trying to do? It's a little confusing just looking at your code.

    Basically, you need a type that you want to malloc that you sizeof and pass to malloc, and a pointer to that type that you assign the result of malloc to.

  3. #3
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    So should it be:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    #define MAX_STRING 128
    
    typedef char String[MAX_STRING];
    
    typedef struct {
            String Name;
            double Size;
    } ArrayType;
    //--------------------------------------------------------------------
    int main(void) {
    
    ArrayType *Array = malloc(sizeof(Array));
    
    }
    As much as I try to understand pointers, i get more confused

  4. #4
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    more like sizeof(*Array) or sizeof(ArrayType)

    sizeof(Array) would just give you the size of the pointer to ArrayType, which is probably only a couple of bytes (typically 4 on 32-bit processors, 8 on 64-bit processors), which is probably too small for ArrayType.

    free it when you're done.

    >As much as I try to understand pointers, i get more confused

    pointers are just variables that hold an address to another variable. When you access the other variable through the pointer, that's called dereferencing.

    dereference with the * operator. like this:
    Code:
    int i; /* 'integer' i */
    int *p; /* 'pointer to integer' p */
    
    p = &i; /* put the address of the variable i into the pointer to integer p. */
    *p = 15 ; /* dereferences p, and assigns 15 to the integer i */
    
    printf("&#37;d %d\n" , *p, i ); /* prints "15 15" */
    http://www.cprogramming.com/tutorial/c/lesson6.html
    http://faq.cprogramming.com/cgi-bin/...&id=1043284351
    Last edited by robwhit; 03-02-2008 at 12:42 AM.

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