[C400-L] Re: dynamic array of pointers

[Barbara Morris <bmorris@xxxxxxxxxx>]

James Rich wrote:
> 
> Hey everyone,
> 
> I need to make an array of pointers to struct that can be dynamically
> resized.  Right now i have this:
> 
> typedef struct _screenfields
> {
>   unsigned int totalfields;
>   field5250 fields[1782];
> } screenfields;
> 
> screenfields *fields5250[10];
> 
> I need to make the fields5250 array be dynamic (instead of only 10
> elements).  I think I need to do:
> 
> screenfields **fields5250;
> 
> I don't know how to do the malloc() properly for that, though.  Currently
> for my static array of pointers I do this:
> 
>   fields5250[0] = (screenfields *) malloc (sizeof (screenfields));
> 
> Which works great.  I think I should be able to keep the same statement to
> allocate each element using a dynamic array, but I don't know how to
> allocate the array itself.  I think I don't have to allocate the array
> itself at all, since the array is just a pointer to the first element in
> the array.  But it's been seg faulting, so I think I'm doing something
> wrong.
> 

An array of pointers is an array of data just like an array of
integers.  For a dynamic array of integers, you'd have to allocate the
array; same with the array of pointers.

  fields5250 = (screenfields **) malloc (num * sizeof(screenfields *));

Me, I like to use typedef:

  typedef screenfields *screenfieldsPtr;
  screenfieldsPtr *fields5250;

  fields5250 = (screenfieldsPtr *) malloc (num *
sizeof(screenfieldsPtr));
  fields5250[0] = whatever