Something

int decoupe(char *buff,cut *w)
{
     char *ptr=buff,*tmp=NULL;
     tmp=ptr;

  while(*ptr!='\0')
  {
   for (; (*ptr) && (*ptr != ' ') && (*ptr!='\0') && (!FIN_LIGNE (*ptr)); ptr++);

        w->tab = (char **) realloc (w->tab,sizeof (char *) * (w->argu + 1));
        w->tab[w->argu] = (char *) malloc (sizeof (char) * (ptr - tmp + 1));
        strncpy (w->tab[w->argu], tmp, ptr - tmp);
        w->tab[w->argu][ptr - tmp] = 0;

        w->argu++;

        tmp=++ptr;
   }
     return 0;
}