manual/examples/rprintf.c

   1 /* Printf Extension Example
   2    Copyright (C) 1991-2014 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU General Public License
   6    as published by the Free Software Foundation; either version 2
   7    of the License, or (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, if not, see <http://www.gnu.org/licenses/>.
  16 */
  17
  18 #include <stdio.h>
  19 #include <stdlib.h>
  20 #include <printf.h>
  21
  22 /*@group*/
  23 typedef struct
  24 {
  25   char *name;
  26 }
  27 Widget;
  28 /*@end group*/
  29
  30 int
  31 print_widget (FILE *stream,
  32               const struct printf_info *info,
  33               const void *const *args)
  34 {
  35   const Widget *w;
  36   char *buffer;
  37   int len;
  38
  39   /* Format the output into a string. */
  40   w = *((const Widget **) (args[0]));
  41   len = asprintf (&buffer, "<Widget %p: %s>", w, w->name);
  42   if (len == -1)
  43     return -1;
  44
  45   /* Pad to the minimum field width and print to the stream. */
  46   len = fprintf (stream, "%*s",
  47                  (info->left ? -info->width : info->width),
  48                  buffer);
  49
  50   /* Clean up and return. */
  51   free (buffer);
  52   return len;
  53 }
  54
  55
  56 int
  57 print_widget_arginfo (const struct printf_info *info, size_t n,
  58                       int *argtypes)
  59 {
  60   /* We always take exactly one argument and this is a pointer to the
  61      structure..  */
  62   if (n > 0)
  63     argtypes[0] = PA_POINTER;
  64   return 1;
  65 }
  66
  67
  68 int
  69 main (void)
  70 {
  71   /* Make a widget to print. */
  72   Widget mywidget;
  73   mywidget.name = "mywidget";
  74
  75   /* Register the print function for widgets. */
  76   register_printf_function ('W', print_widget, print_widget_arginfo);
  77
  78   /* Now print the widget. */
  79   printf ("|%W|\n", &mywidget);
  80   printf ("|%35W|\n", &mywidget);
  81   printf ("|%-35W|\n", &mywidget);
  82
  83   return 0;
  84 }