Re: saving GArray contents to binary file

[edward hage <edha xs4all nl>]

Maciej Katafiasz wrote:
> Dnia 03-10-2004, nie o godzinie 12:19 +0200, edward hage napisał(a):
>
> > I want to save a GArray of struct to a binairy file, but I get stuck somehow.
> >
> >   for (i=0; i<array->len; i++)
> >   {
> >     fwrite(&array[i], sizeof (typDing), 1, fp);
>
>               ^^^^^^^^^
>
> I don't think that's right thing to do, GArray is not C array
>
>
> > I also want to save structs with GArrays inside them, like:
> > typedef struct
> > {
> >   gchar *name;
> >   GArray *attached;
> > } typDing2;
> >
> > How to save those?
>
>
> you need to save them struct-by-struct, and then read it back
> reconstructing GArray, in general. You could also do some GValue
> transformation foo, but that would be probably more hassle than gain, so
> unless you have 1000 different types with GArrays that can change at
> runtime, better go easy route and just manually save it
>
> HTH,
> Maciej


I found a way to save GArray's to file, in fact a GArray is just a struct. All the data 
about size is known in GRealArray which is used by all the g_array*** functions. This type 
is casted to GArray which has less info.

So my idea to save GArray's is to cast it back to GRealArray, save the GRealArray with 
array->data = NULL. The real data is stored after the GRealArray. A function is written to 
save everything needed. A special function to read the array will read the GRealArray and 
the data and put the data in the GRealArray, and cast it back to GArray:

typedef struct
{
  guint8 *data;
  guint   len;
  guint   alloc;
  guint   elt_size;
  guint   zero_terminated : 1;
  guint   clear : 1;
} GRealArray;

GArray *save_array_to_file (GArray *farray, FILE *fp)
{
  GRealArray *array = (GRealArray*) farray;
  guint8 *data_begin;
  data_begin = array -> data;

  array -> data = NULL;
  fwrite(array, sizeof(GRealArray),1, fp);
  gint length = array ->elt_size * array ->len;
  gint i;
  for (i=0; i < length; i++)
  {
    fwrite(&(data_begin[i]),sizeof(guint8),1,fp);
  }
  return ((GArray *) array);
}

void read_array_from_file (GArray *farray, FILE *fp)
{
  GRealArray *array = (GRealArray *) farray;
  fread(array, sizeof(GRealArray),1, fp);
  gint length = array ->elt_size * array ->len;
  gint i;
  guint8 *data_string= g_malloc(sizeof(guint8)*length);
  for (i=0; i < length; i++)
  {
    fread(&(data_string[i]),sizeof(guint8),1,fp);
  }
  array -> data = data_string;
  //attention: previous initialisation of input farray is overwritten (zero_terminated 
bit, etc.)
  // if farray not previously initialised then Segmentation fault will occur
}

MY QUESTIONS:
1) I want to save GArray's of structs with pointers to data, for which data in turn also 
have pointers to other data. Is there a good way to save the whole data-tree at once to a 
binary file?
2) Does anybody else already developed more secure or better (?) ways to save and load a 
GArray? Now not so pretty is that in read_array_from_file the GArray *farray must already 
be initialised with arbitrary values/ arbitrary because they get overwritten anyway by the 
info from the file)

Greetings, Edward