socket inet_ pton() inet_ Ntop() function (a new network address translation function, which converts the expression format and numerical format to each other. The old ones are inet_aton(), INET_ ntoa

New network address translation function ：

Remove the buffer from CP At the beginning Internet The representation format of the number is converted to binary network format , And the interface type AF The results are stored from BUF In the start buffer .

The function of this code is similar , What's the difference ？

serv_addr.sin_addr.s_addr = inet_addr("192.168.1.116");

take Internet Host address from CP The numbers and dot symbols in are converted into binary data in network byte order .

New network address translation function inet_pton() and inet_ntop()
These two functions follow IPv6 Functions that appear , about IPv4 Address and IPv6 All addresses apply , Function p and n Each represents the expression （presentation） And numbers （numeric）. The expression format of address （presentation） Usually ASCII character string , The numerical format （numeric） Is the binary value stored in the socket address structure .

#include <arpa/inet.h>
int inet_pton(int family, const char *strptr, void *addrptr);     // Will be dotted decimal ip The address is converted into a numeric format for network transmission 
         Return value ： If successful 1, If the input is not a valid expression 0, In case of error -1
 
const char * inet_ntop(int family, const void *addrptr, char *strptr, size_t len);     // Convert numerical format to dot decimal ip Address format 
         Return value ： If successful, a pointer to the structure , In case of error NULL

（1） Of these two functions family The parameter can be either AF_INET（ipv4） It can also be AF_INET6（ipv6）. If , Take an unsupported address family as family Parameters , Both functions return an error , And will errno Set as EAFNOSUPPORT.
（2） The first function attempts to convert from strptr The string that the pointer points to , And pass addrptr The pointer holds the binary result , If successful, the return value is 1, Otherwise, if specified family The input string is not a valid expression format , So the return value is zero 0.
（3）inet_ntop Do the opposite conversion , From the numerical format （addrptr） Convert to expression （strptr).inet_ntop Functional strptr Parameter cannot be a null pointer . The caller must allocate memory for the target storage unit and specify its size , When the call succeeds , This pointer is the return value of the function .len Parameter is the size of the target storage unit , To prevent the function from overflowing its caller's buffer . If len Too small , Not enough to hold expression results , Then return a null pointer , Juxtaposition as errno by ENOSPC.

Reference article 1：inet_pton() and inet_ntop() Function details

Reference article 2：IP Address translation function :inet_pton