shachaf@iodine:~/fmt$ cat main.c
#include <stdio.h>
#include <time.h>

#define CUSTOM_FMT_TYPES \
  FMT_TYPE(struct tm *, 123)

#include "fmt.h"

int custom_fmt_arg(char *buf, size_t size, FmtArg arg, FmtSpec spec) {
  if (arg.type ==  123) {
    char timefmt_buf[spec.custom_len + 1];
    char *timefmt = timefmt_buf;
    if (spec.custom_len > 0) {
      memcpy(timefmt_buf, spec.custom_start, spec.custom_len);
      timefmt[spec.custom_len] = '\0';
    } else {
      timefmt = "%Y-%m-%d";
    }
    struct tm *tm = *(struct tm **)arg.data;
    size_t len = strftime(buf, size, timefmt, tm);
    return len;
  }
  return -1;
}

int main(int argc, char **argv) {
  char x = 'x';
  time_t now = time(0);
  struct tm *tm = localtime(&now);

  outfmt("hello {} {}\n", 123, "hi");
  outfmt("hello {:c}\n", x);
  outfmt("hello {:05} 0x{:05x}\n", 123, 0xa66e);
  outfmt("no arguments\n");
  outfmt("positional arguments: {1:c}{0:c}{2:c}{2:c}{3:c}\n", 'e', 'h', 'l', 'o');
  outfmt("pointers: {:p} {:p}\n", "abc", (void *)0);
  outfmt("custom formatting: now is {|%Y-%m-%d %H:%M:%S} (default format: {0})\n", tm);

  outfmt("{} arguments\n", argc);
  for (int i = 0; i < argc; i++) {
    outfmt("  argument {}: {}\n", i, argv[i]);
  }

  return 0;
}
shachaf@iodine:~/fmt$ gcc -Wall -g -o main main.c && ./main test
hello 123 hi
hello x
hello 00123 0x0a66e
no arguments
positional arguments: hello
pointers: 0x55b8f93b83a1 (nil)
custom formatting: now is 2019-04-21 22:06:09 (default format: 2019-04-21)
2 arguments
  argument 0: ./main
  argument 1: test