ee161acv@sdccs5.UUCP (03/02/84)
I want to have an element in a structure that points to the
end of the structure, but I don't want any space allocated
by 'C' for that element. The reason for this is that I want
the structure to have varying sizes, with the size depending
on certain other parameters. The following is the kind of
thing I want:
------------------------------
struct stuff
{
int numchars; /* Size of remainder of structure */
char chars[]; /* Allocate numchars chars for this
element */
/*###6 [cc] warning: illegal zero sized structure member: chars%%%*/
};
main ()
{
int num; /* User input */
struct stuff *block; /* -> node to allocate */
printf ("How many characters to allocate? ");
scanf ("%d", &num); /* Request info */
block = (struct stuff *)calloc(1, sizeof(struct stuff) + num);
/* Allocate enough memory for the
structure and the extra bytes */
block->numchars = num; /* Etc. */
/* block->chars[0] = ... */
}
------------------------------
Of course this program runs (the warning does not stop it from
compiling), but I also want to suppress the warning. Is there
any provision in C to allow me to do this? Of course, I want
the character string to be stored WITHIN the structure (as above)
and NOT a character pointer to some string outside the structure.
Also, I can't say that the end of the string is the first '\0'
character, because I want them to be allowed in the string.
In the mean time, I was able to solve the problem (with a bit
of a comprimise on neatness) with this:
------------------------------
#define FUDGEFACTOR sizeof(char *)
#define SIZEOF(type) (sizeof(type) - FUDGEFACTOR)
struct stuff
{
int numchars; /* Size of remainder of structure */
char chars[FUDGEFACTOR]; /* Allocate numchars chars for this
element */
};
main ()
{
int num; /* User input */
struct stuff *block; /* -> node to allocate */
printf ("How many characters to allocate? ");
scanf ("%d", &num); /* Request info */
block = (struct stuff *)calloc(1, SIZEOF(struct stuff) + num);
/* Allocate enough memory for the
structure and the extra bytes */
block->numchars = num; /* Etc. */
/* block->chars[0] = ... */
}
------------------------------------
I would like to find a better way.
Thanks for any suggestions,
Victor Romano.
P. S. I also noticed that the directory files on 4.2 use
dynamic structure sizes as well, so there's one application
of this!
=========
Meek and obedient you follow the leader
down well trodden corridors into the valley of steel!
-PF