Re: The following works in Linux

From:

Maxim Yegorushkin <maxim.yegorushkin@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 3 Dec 2008 07:08:58 -0800 (PST)

Message-ID:

<1e2e6023-d2a9-49ab-a34a-5f20a53e0f71@v42g2000yqv.googlegroups.com>

On Dec 3, 12:34 pm, "parag_p...@hotmail.com" <parag_p...@hotmail.com>
wrote:

#include <stdio.h>

struct _table_model_entry {
  struct _table_model_entry *next;
  int line_nr;
  int nr_fields;
  char *fields[0]; /* User defined */
};

int main(){
char * a,*b,*c,*d;
struct _table_model_entry tb;
tb.fields[0] = a;
tb.fields[1] = b;
}

But I dont get the use of an array size of 0 for member fields in the
struct _table_model_entry .

char *fields[0] is a gcc extension similar to C99 flexible array
member. You can find more information here:
http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Zero-Length.html#Zero-Length

The storage for that member must be allocated manually. It is normally
used with dynamic allocation:

    #include <stdlib.h>

    struct _table_model_entry {
      struct _table_model_entry *next;
      int line_nr;
      int nr_fields;
      char *fields[0]; /* User defined */
    };

    typedef struct _table_model_entry tme;

    tme* tme_alloc(int fields_count)
    {
        return (tme*)malloc(
              sizeof(tme)
              /* space for tme::fields member*/
            + sizeof(char*) * fields_count
            );
    }

    int main()
    {
        tme* p = tme_alloc(2);
        p->fields[0] = NULL;
        p->fields[1] = NULL;
    }

--
Max