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man:inet_net_ntop

INET_NET_PTON(3) Linux Programmer's Manual INET_NET_PTON(3)

NAME

     inet_net_pton, inet_net_ntop - Internet network number conversion

SYNOPSIS

     #include <arpa/inet.h>
     int inet_net_pton(int af, const char *pres,
                       void *netp, size_t nsize);
     char *inet_net_ntop(int af, const void *netp, int bits,
                         char *pres, size_t psize);
     Link with -lresolv.
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     inet_net_pton(), inet_net_ntop():
         Since glibc 2.20:
             _DEFAULT_SOURCE
         Before glibc 2.20:
             _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

     These  functions  convert  network  numbers between presentation (i.e.,
     printable) format and network (i.e., binary) format.
     For both functions, af specifies the address family for the conversion;
     the only supported value is AF_INET.
 inet_net_pton()
     The  inet_net_pton()  function  converts pres, a null-terminated string
     containing an Internet network number in presentation format to network
     format.   The result of the conversion, which is in network byte order,
     is placed in the buffer pointed to by net.  (The  netp  argument  typi-
     cally  points  to  an in_addr structure.)  The nsize argument specifies
     the number of bytes available in netp.
     On success, inet_net_pton() returns the number of bits in  the  network
     number  field  of  the  result placed in netp.  For a discussion of the
     input presentation format and the return value, see NOTES.
     Note: the buffer pointed to by netp should be zeroed out before calling
     inet_net_pton(),  since  the  call  writes  only  as  many bytes as are
     required for the network number (or  as  are  explicitly  specified  by
     pres), which may be less than the number of bytes in a complete network
     address.
 inet_net_ntop()
     The inet_net_ntop() function converts the network number in the  buffer
     pointed  to  by  netp to presentation format; *netp is interpreted as a
     value in network byte order.  The bits argument specifies the number of
     bits in the network number in *netp.
     The  null-terminated presentation-format string is placed in the buffer
     pointed to by pres.  The psize argument specifies the number  of  bytes
     available  in  pres.  The presentation string is in CIDR format: a dot-
     ted-decimal number representing the  network  address,  followed  by  a
     slash, and the size of the network number in bits.

RETURN VALUE

     On  success,  inet_net_pton() returns the number of bits in the network
     number.  On error, it returns -1, and errno  is  set  to  indicate  the
     cause of the error.
     On  success,  inet_net_ntop() returns pres.  On error, it returns NULL,
     and errno is set to indicate the cause of the error.

ERRORS

     EAFNOSUPPORT
            af specified a value other than AF_INET.
     EMSGSIZE
            The size of the output buffer was insufficient.
     ENOENT (inet_net_pton()) pres was not in correct presentation format.

CONFORMING TO

     The inet_net_pton() and inet_net_ntop() functions are nonstandard,  but
     widely available.

NOTES

 Input presentation format for inet_net_pton()
     The network number may be specified either as a hexadecimal value or in
     dotted-decimal notation.
     Hexadecimal values are indicated by an initial "0x" or "0X".  The hexa-
     decimal digits populate the nibbles (half octets) of the network number
     from left to right in network byte order.
     In dotted-decimal notation, up to four octets are specified, as decimal
     numbers  separated  by  dots.   Thus,  any  of  the following forms are
     accepted:
         a.b.c.d
         a.b.c
         a.b
         a
     Each part is a number in the range 0 to 255 that populates one byte  of
     the resulting network number, going from left to right, in network-byte
     (big endian) order.  Where a part is omitted, the resulting byte in the
     network number is zero.
     For either hexadecimal or dotted-decimal format, the network number can
     optionally be followed by a slash and a number in the range  0  to  32,
     which specifies the size of the network number in bits.
 Return value of inet_net_pton()
     The  return  value of inet_net_pton() is the number of bits in the net-
     work number field.  If the input presentation string terminates with  a
     slash  and  an  explicit  size value, then that size becomes the return
     value of  inet_net_pton().   Otherwise,  the  return  value,  bits,  is
     inferred as follows:
  • If the most significant byte of the network number is greater than

or equal to 240, then bits is 32.

  • Otherwise, if the most significant byte of the network number is

greater than or equal to 224, then bits is 4.

  • Otherwise, if the most significant byte of the network number is

greater than or equal to 192, then bits is 24.

  • Otherwise, if the most significant byte of the network number is

greater than or equal to 128, then bits is 16.

  • Otherwise, bits is 8.
     If  the  resulting  bits  value from the above steps is greater than or
     equal to 8, but the number of octets specified in  the  network  number
     exceed  bits/8,  then bits is set to 8 times the number of octets actu-
     ally specified.

EXAMPLE

     The  program  below  demonstrates  the  use  of   inet_net_pton()   and
     inet_net_ntop().   It  uses inet_net_pton() to convert the presentation
     format network address provided in its first command-line  argument  to
     binary  form,  displays the return value from inet_net_pton().  It then
     uses inet_net_ntop() to convert the binary form  back  to  presentation
     format, and displays the resulting string.
     In order to demonstrate that inet_net_pton() may not write to all bytes
     of its netp argument, the program allows an  optional  second  command-
     line   argument,   a  number  used  to  initialize  the  buffer  before
     inet_net_pton() is called.  As its final line of  output,  the  program
     displays  all  of  the  bytes of the buffer returned by inet_net_pton()
     allowing the  user  to  see  which  bytes  have  not  been  touched  by
     inet_net_pton().
     An  example run, showing that inet_net_pton() infers the number of bits
     in the network number:
         $ ./a.out  193.168  inet_net_pton()  returned:  24  inet_net_ntop()
         yielded:  193.168.0/24 Raw address:              c1a80000
     Demonstrate  that inet_net_pton() does not zero out unused bytes in its
     result buffer:
         $  ./a.out  193.168   0xffffffff   inet_net_pton()   returned:   24
         inet_net_ntop()     yielded:      193.168.0/24     Raw     address:
         c1a800ff
     Demonstrate that inet_net_pton() will widen the inferred  size  of  the
     network  number,  if  the  supplied number of bytes in the presentation
     string exceeds the inferred value:
         $    ./a.out    193.168.1.128    inet_net_pton()    returned:    32
         inet_net_ntop()    yielded:     193.168.1.128/32    Raw    address:
         c1a80180
     Explicitly specifying the size of  the  network  number  overrides  any
     inference about its size (but any extra bytes that are explicitly spec-
     ified will still be used by inet_net_pton():  to  populate  the  result
     buffer):
         $    ./a.out    193.168.1.128/24   inet_net_pton()   returned:   24
         inet_net_ntop()     yielded:      193.168.1/24     Raw     address:
         c1a80180
 Program source
     /* Link with "-lresolv" */
     #include <arpa/inet.h> #include <stdio.h> #include <stdlib.h>
     #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                             } while (0)
     int main(int argc, char *argv[]) {
         char buf[100];
         struct in_addr addr;
         int bits;
         if (argc < 2) {
             fprintf(stderr,
                     "Usage: %s presentation-form [addr-init-value]\n",
                     argv[0]);
             exit(EXIT_FAILURE);
         }
         /* If argv[2] is supplied (a numeric value), use it to initialize
            the output buffer given to inet_net_pton(), so that we can see
            that inet_net_pton() initializes only those bytes needed for
            the network number. If argv[2] is not supplied, then initialize
            the buffer to zero (as is recommended practice). */
         addr.s_addr = (argc > 2) ? strtod(argv[2], NULL) : 0;
         /* Convert presentation network number in argv[1] to binary */
         bits = inet_net_pton(AF_INET, argv[1], &addr, sizeof(addr));
         if (bits == -1)
             errExit("inet_net_ntop");
         printf("inet_net_pton() returned: %d\n", bits);
         /* Convert binary format back to presentation, using 'bits'
            returned by inet_net_pton() */
         if (inet_net_ntop(AF_INET, &addr, bits, buf, sizeof(buf)) == NULL)
             errExit("inet_net_ntop");
         printf("inet_net_ntop() yielded:  %s\n", buf);
         /* Display 'addr' in raw form (in network byte order), so we can
            see bytes not displayed by inet_net_ntop(); some of those bytes
            may not have been touched by inet_net_ntop(), and so will still
            have any initial value that was specified in argv[2]. */
         printf("Raw address:              %x\n", htonl(addr.s_addr));
         exit(EXIT_SUCCESS); }

SEE ALSO

     inet(3), networks(5)

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 INET_NET_PTON(3)

/data/webs/external/dokuwiki/data/pages/man/inet_net_ntop.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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