t.c

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#include <arpa/inet.h>
#include <stdio.h>
#include <stdint.h>

struct addr_t {
  union {
    uint8_t u8[16];
    uint16_t u16[8];
  } addr;
};

const unsigned char hex[] = "0123456789ABCDEF";

size_t
print_addr(struct addr_t *addr, char *buf, size_t len) {
  int i;
  char *p = buf;
  *p++ = '[';

  for (i=0; i < 16; i += 2) {
    if (i) {
      *p++ = ':';
    }
    *p++ = hex[(addr->addr.u8[i] & 0xf0) >> 4];
    *p++ = hex[addr->addr.u8[i] & 0x0f];
    *p++ = hex[(addr->addr.u8[i+1] & 0xf0) >> 4];
    *p++ = hex[addr->addr.u8[i+1] & 0x0f];
  }
  
  *p++ = ']';

  if (buf + len - p < 6)
    return 0;

  p += snprintf((char *)p, buf + len - p + 1, ":%d", 50000);

  return p - buf;
}

int main() {
  struct addr_t addr;
  char  buf[100];
  size_t result;

  addr.addr.u16[0] = htons(0x0011);
  addr.addr.u16[1] = htons(0x2233);
  addr.addr.u16[2] = htons(0x4455);
  addr.addr.u16[3] = htons(0x6677);
  addr.addr.u16[4] = htons(0x8899);
  addr.addr.u16[5] = htons(0xaabb);
  addr.addr.u16[6] = htons(0xccdd);
  addr.addr.u16[7] = htons(0xeeff);
 
  result = print_addr(&addr, buf, 48);
  buf[result] = '\0';

  printf("%s\n", buf);
  return 0;
}