1  /* Printf Extension Example
       2     Copyright (C) 1991-2023 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, see <https://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  }