1 /* Printf Extension Example
2 Copyright (C) 1991-2022 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
print_widget(FILE * stream,const struct printf_info * info,const void * const * args)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
print_widget_arginfo(const struct printf_info * info,size_t n,int * argtypes)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
main(void)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 }
85