inet_ntop函数和inet

#include<arpa/inet.h>
int inet_pton(int family, const char *strptr, void *addrptr);返回：若成功则为1,若输入不是有效的表达格式则为0,若出错则为-1
const char *inet_ntop(int family, const void *addrptr, char *strptr, size_t len);返回：若成功则为指向结果的指针， 若出错则为NULL

这两个函数的family参数既可以是AF_INET，也可以是AF_INET6。如果以不被支持的地址族作为family的参数，这两个函数就都返回一个错误，并将errno置为EAFNOSUPPORT。

第一个函数尝试转换由strptr指针所指的字符串，并通过addrptr指针存放二进制结果。若成功则返回1,否则如果对所指定的family而言输入的字符串不是有效的表达式，那么值为0。

inet_ntop进行相反的转换，从数值格式（addrptr）转换到表达格式（strptr）。len参数是目标存储单元的大小，以免该函数溢出其调用者的缓冲区。为有助于指定这个大小，在

INET_NTOP(3)               Linux Programmer's Manual              INET_NTOP(3)NAMEinet_ntop - convert IPv4 and IPv6 addresses from binary to text formSYNOPSIS#include <arpa/inet.h>const char *inet_ntop(int af, const void *src,char *dst, socklen_t size);DESCRIPTIONThis  function  converts  the  network  address structure src in the afaddress family into a character string.  The resulting string is copiedto the buffer pointed to by dst, which must be a non-null pointer.  Thecaller specifies the number of bytes available in this  buffer  in  theargument size.inet_ntop()  extends  the  inet_ntoa(3)  function  to  support multipleaddress families, inet_ntoa(3) is now considered to  be  deprecated  infavor  of  inet_ntop().   The  following address families are currentlysupported:AF_INETsrc points to a struct in_addr (in network byte order) which  isconverted  to an IPv4 network address in the dotted-decimal for‐mat,  "ddd.ddd.ddd.ddd".   The  buffer  dst  must  be  at  leastINET_ADDRSTRLEN bytes long.AF_INET6src points to a struct in6_addr (in network byte order) which isconverted to a representation of this address in the most appro‐priate IPv6 network address format for this address.  The bufferdst must be at least INET6_ADDRSTRLEN bytes long.RETURN VALUEOn success, inet_ntop() returns a non-null pointer  to  dst.   NULL  isreturned if there was an error, with errno set to indicate the error.ERRORSEAFNOSUPPORTaf was not a valid address family.ENOSPC The  converted  address  string  would  exceed the size given bysize.ATTRIBUTESFor  an  explanation  of  the  terms  used   in   this   section,   seeattributes(7).┌────────────┬───────────────┬────────────────┐│Interface   │ Attribute     │ Value          │├────────────┼───────────────┼────────────────┤│inet_ntop() │ Thread safety │ MT-Safe locale │└────────────┴───────────────┴────────────────┘CONFORMING TOPOSIX.1-2001,  POSIX.1-2008.   Note  that  RFC 2553 defines a prototypewhere the last argument size is of type size_t.   Many  systems  followRFC 2553.   Glibc  2.0  and  2.1  have  size_t,  but 2.2 and later havesocklen_t.BUGSAF_INET6 converts IPv4-mapped IPv6 addresses into an IPv6 format.EXAMPLESee inet_pton(3).SEE ALSOgetnameinfo(3), inet(3), inet_pton(3)COLOPHONThis page is part of release 4.04 of the Linux  man-pages  project.   Adescription  of  the project, information about reporting bugs, and thelatest    version    of    this    page,    can     be     found     athttp://www.kernel.org/doc/man-pages/.Linux                             2015-08-08                      INET_NTOP(3)INET_PTON(3)               Linux Programmer's Manual              INET_PTON(3)NAMEinet_pton - convert IPv4 and IPv6 addresses from text to binary formSYNOPSIS#include <arpa/inet.h>int inet_pton(int af, const char *src, void *dst);DESCRIPTIONThis  function converts the character string src into a network addressstructure in the af address family, then  copies  the  network  addressstructure to dst.  The af argument must be either AF_INET or AF_INET6.The following address families are currently supported:AF_INETsrc  points  to  a  character  string containing an IPv4 networkaddress in dotted-decimal format, "ddd.ddd.ddd.ddd",  where  dddis a decimal number of up to three digits in the range 0 to 255.The address is converted to a struct in_addr and copied to  dst,which must be sizeof(struct in_addr) (4) bytes (32 bits) long.AF_INET6src  points  to  a  character  string containing an IPv6 networkaddress.  The address is converted  to  a  struct  in6_addr  andcopied  to dst, which must be sizeof(struct in6_addr) (16) bytes(128 bits) long.  The allowed formats for IPv6 addresses  followthese rules:1. The  preferred format is x:x:x:x:x:x:x:x.  This form consistsof eight hexadecimal  numbers,  each  of  which  expresses  a16-bit value (i.e., each x can be up to 4 hex digits).2. A  series  of  contiguous zero values in the preferred formatcan be abbreviated to ::.  Only one instance of :: can  occurin   an   address.    For   example,   the  loopback  address0:0:0:0:0:0:0:1 can be  abbreviated  as  ::1.   The  wildcardaddress, consisting of all zeros, can be written as ::.3. An alternate format is useful for expressing IPv4-mapped IPv6addresses.  This  form  is  written  as  x:x:x:x:x:x:d.d.d.d,where  the  six leading xs are hexadecimal values that definethe six most-significant 16-bit pieces of the address  (i.e.,96  bits), and the ds express a value in dotted-decimal nota‐tion that defines  the  least  significant  32  bits  of  theaddress.     An    example    of    such    an   address   is::FFFF:204.152.189.116.See RFC 2373 for further details on the representation  of  IPv6addresses.RETURN VALUEinet_pton() returns 1 on success (network address was successfully con‐verted).  0 is returned if src does not contain a character string rep‐resenting  a valid network address in the specified address family.  Ifaf does not contain a valid address family, -1 is returned and errno isset to EAFNOSUPPORT.ATTRIBUTESFor   an   explanation   of   the  terms  used  in  this  section,  seeattributes(7).┌────────────┬───────────────┬────────────────┐│Interface   │ Attribute     │ Value          │├────────────┼───────────────┼────────────────┤│inet_pton() │ Thread safety │ MT-Safe locale │└────────────┴───────────────┴────────────────┘
CONFORMING TOPOSIX.1-2001, POSIX.1-2008.NOTESUnlike  inet_aton(3)  and  inet_addr(3),  inet_pton()   supports   IPv6addresses.   On the other hand, inet_pton() accepts only IPv4 addressesin dotted-decimal notation, whereas inet_aton(3) and inet_addr(3) allowthe  more general numbers-and-dots notation (hexadecimal and octal num‐ber formats, and formats that  don't  require  all  four  bytes  to  beexplicitly   written).    For  an  interface  that  handles  both  IPv6addresses, and IPv4 addresses in numbers-and-dots notation, see  getad‐drinfo(3).BUGSAF_INET6  does  not  recognize IPv4 addresses.  An explicit IPv4-mappedIPv6 address must be supplied in src instead.EXAMPLEThe program below demonstrates the use of inet_pton() and inet_ntop(3).Here are some example runs:$ ./a.out i6 0:0:0:0:0:0:0:0::$ ./a.out i6 1:0:0:0:0:0:0:81::8$ ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116::ffff:204.152.189.116Program source#include <arpa/inet.h>#include <stdio.h>#include <stdlib.h>#include <string.h>intmain(int argc, char *argv[]){unsigned char buf[sizeof(struct in6_addr)];int domain, s;char str[INET6_ADDRSTRLEN];if (argc != 3) {fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);exit(EXIT_FAILURE);}domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :(strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);s = inet_pton(domain, argv[2], buf);if (s <= 0) {if (s == 0)fprintf(stderr, "Not in presentation format");elseperror("inet_pton");exit(EXIT_FAILURE);}if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {perror("inet_ntop");exit(EXIT_FAILURE);}printf("%s\n", str);exit(EXIT_SUCCESS);}SEE ALSOgetaddrinfo(3), inet(3), inet_ntop(3)COLOPHONThis  page  is  part of release 4.04 of the Linux man-pages project.  Adescription of the project, information about reporting bugs,  and  thelatest     version     of     this    page,    can    be    found    athttp://www.kernel.org/doc/man-pages/.Linux                             2015-08-08                      INET_PTON(3)

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