IP地址转换函数

#include <arpa/inet.h>

/* Convert Internet host address from numbers-and-dots notation in CP
   into binary data and store the result in the structure INP.  */
int inet_aton (const char *__cp, struct in_addr *__inp);

/* Convert Internet host address from numbers-and-dots notation in CP
   into binary data in network byte order.  */
in_addr_t inet_addr (const char *__cp);

/* Convert Internet number in IN to ASCII representation.  The return value
   is a pointer to an internal array containing the string.  */
char *inet_ntoa (struct in_addr __in);

#include <arpa/inet.h>

/* Convert from presentation format of an Internet number in buffer
   starting at CP to the binary network format and store result for
   interface type AF in buffer starting at BUF.  */
int inet_pton (int __af, const char *__restrict __cp,
              void *__restrict __buf);

/* Convert a Internet address in binary network format for interface
   type AF in buffer starting at CP to presentation form and place
   result in buffer of length LEN astarting at BUF.  */
const char *inet_ntop (int __af, const void *__restrict __cp,
                  char *__restrict __buf, socklen_t __len);

1 #define INET_ADDRSTRLEN 16    /* for IPv4 dotted-decimal */
2 #define INET6_ADDRSTRLEN 46     /* for IPv6 hex string */