center.c

   1 #define _POSIX_C_SOURCE 200809L
   2 #define _XOPEN_SOURCE
   3 #include <fcntl.h>
   4 #include <locale.h>
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <sys/ioctl.h>
   8 #include <sys/stat.h>
   9 #include <sys/types.h>
  10 #include <termios.h>
  11 #include <unistd.h>
  12 #include <wchar.h>
  13
  14 #define ERR(str) { perror(str); err = EXIT_FAILURE; goto end; }
  15
  16 int main()
  17 {
  18         if (setlocale(LC_ALL, "") == NULL) {
  19                 perror("setlocale");
  20                 exit(EXIT_FAILURE);
  21         }
  22
  23         char *buf = NULL;
  24         size_t siz = 0;
  25         ssize_t len;
  26         int err = EXIT_SUCCESS;
  27
  28         int tty_fd = open("/dev/tty", O_RDWR);
  29         if (tty_fd < 0) {
  30                 perror("open");
  31                 return EXIT_FAILURE;
  32         }
  33
  34         while ((len = getline(&buf, &siz, stdin)) > 0) {
  35                 struct winsize ws;
  36                 if (ioctl(tty_fd, TIOCGWINSZ, &ws) < 0) ERR("ioctl")
  37
  38                 int term_width = ws.ws_col;
  39
  40                 char *ptr = buf;
  41                 char *last = ptr;
  42                 int str_width = 0;
  43                 mbstate_t mbs = {0};
  44
  45                 while (len > 0) {
  46                         wchar_t wc;
  47
  48                         size_t adv = mbrtowc(&wc, ptr, len, &mbs);
  49                         if (adv == (size_t) -1 || adv == (size_t) -2) ERR("mbrtowc")
  50
  51                         int width = wcwidth(wc);
  52                         if (width > 0)
  53                                 str_width += width;
  54
  55                         if (*ptr == '\n' || str_width >= term_width - 12) {
  56                                 for (int i = (term_width - str_width) / 2; i > 0; i--)
  57                                         putchar(' ');
  58                                 fwrite(last, 1, ptr - last + 1, stdout);
  59
  60                                 if (*ptr != '\n')
  61                                         putchar('\n');
  62
  63                                 last = ptr + adv;
  64                                 str_width = 0;
  65                         }
  66
  67                         ptr += adv;
  68                         len -= adv;
  69                 }
  70         }
  71
  72         end:
  73         close(tty_fd);
  74
  75         if (buf)
  76                 free(buf);
  77
  78         return err;
  79 }