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INET(3)                    Linux Programmer's ManualINET(3)NAME       inet_aton,    inet_addr,    inet_network,   inet_ntoa,   inet_makeaddr,       inet_lnaof, inet_netof - Internet address manipulation routinesSYNOPSIS       #include <sys/socket.h>       #include <netinet/in.h>       #include <arpa/inet.h>       int inet_aton(const char *cp, struct in_addr *inp);       in_addr_t inet_addr(const char *cp);       in_addr_t inet_network(const char *cp);       char *inet_ntoa(struct in_addr in);       struct in_addr inet_makeaddr(in_addr_t net, in_addr_t host);       in_addr_t inet_lnaof(struct in_addr in);       in_addr_t inet_netof(struct in_addr in);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):       inet_aton(), inet_ntoa():           Since glibc 2.19:               _DEFAULT_SOURCE           In glibc up to and including 2.19:               _BSD_SOURCE || _BSD_SOURCEDESCRIPTION       inet_aton() converts the Internet host address cp from  the  IPv4  num-       bers-and-dots  notation  into  binary  form (in network byte order) and       stores it in the structure that inp  points  to.   inet_aton()  returns       nonzero  if the address is valid, zero if not.  The address supplied in       cp can have one of the following forms:       a.b.c.d   Each of the four numeric parts specifies a byte  of  the  ad-                 dress;  the bytes are assigned in left-to-right order to pro-                 duce the binary address.       a.b.c     Parts a and b specify the first two bytes of the  binary  ad-                 dress.   Part c is interpreted as a 16-bit value that defines                 the rightmost two bytes of the binary address.  This notation                 is  suitable  for  specifying  (outmoded) Class B network ad-                 dresses.       a.b       Part a specifies the first byte of the binary address.   Part                 b is interpreted as a 24-bit value that defines the rightmost                 three bytes of the binary address.  This notation is suitable                 for specifying (outmoded) Class A network addresses.       a         The  value  a is interpreted as a 32-bit value that is stored                 directly into the binary address without any byte  rearrange-                 ment.       In  all  of  the  above  forms, components of the dotted address can be       specified in decimal, octal (with a leading 0), or hexadecimal, with  a       leading  0X).   Addresses in any of these forms are collectively termed       IPV4 numbers-and-dots notation.  The form that uses exactly four  deci-       mal  numbers  is  referred to as IPv4 dotted-decimal notation (or some-       times: IPv4 dotted-quad notation).       inet_aton() returns 1 if the supplied string  was  successfully  inter-       preted, or 0 if the string is invalid (errno is not set on error).       The  inet_addr()  function  converts  the Internet host address cp from       IPv4 numbers-and-dots notation into binary data in network byte  order.       If  the input is invalid, INADDR_NONE (usually -1) is returned.  Use of       this  function  is  problematic  because  -1   is   a   valid   address       (255.255.255.255).    Avoid   its   use   in   favor   of  inet_aton(),inet_pton(3), orgetaddrinfo(3), which provide a cleaner way  to  indi-       cate error return.       The  inet_network() function converts cp, a string in IPv4 numbers-and-       dots notation, into a number in host byte order suitable for use as  an       Internet  network  address.   On  success, the converted address is re-       turned.  If the input is invalid, -1 is returned.       The inet_ntoa() function converts the Internet host address  in,  given       in  network  byte  order,  to a string in IPv4 dotted-decimal notation.       The string is returned in a statically allocated buffer,  which  subse-       quent calls will overwrite.       The inet_lnaof() function returns the local network address part of the       Internet address in.  The returned value is in host byte order.       The inet_netof() function returns the network number part of the Inter-       net address in.  The returned value is in host byte order.       The  inet_makeaddr()  function  is  the  converse  of  inet_netof() and       inet_lnaof().  It returns an Internet host address in network byte  or-       der, created by combining the network number net with the local address       host, both in host byte order.       The  structure  in_addr  as  used  in   inet_ntoa(),   inet_makeaddr(),       inet_lnaof() and inet_netof() is defined in <netinet/in.h> as:           typedef uint32_t in_addr_t;           struct in_addr {               in_addr_t s_addr;           };ATTRIBUTES       For  an  explanation  of  the  terms  used  in  this  section,  see at-tributes(7).       +-------------------------------+---------------+----------------+       |Interface                      | Attribute     | Value          |       +-------------------------------+---------------+----------------+       |inet_aton(), inet_addr(),      | Thread safety | MT-Safe locale |       |inet_network(), inet_ntoa()    |               |                |       +-------------------------------+---------------+----------------+       |inet_makeaddr(), inet_lnaof(), | Thread safety | MT-Safe        |       |inet_netof()                   |               |                |       +-------------------------------+---------------+----------------+CONFORMING TO       inet_addr(), inet_ntoa(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.       inet_aton() is not specified in POSIX.1, but is available on most  sys-       tems.NOTES       On  x86  architectures,  the  host byte order is Least Significant Byte       first (little endian), whereas the network byte order, as used  on  the       Internet, is Most Significant Byte first (big endian).       inet_lnaof(),  inet_netof(),  and  inet_makeaddr() are legacy functions       that assume they are dealing with classful network addresses.  Classful       networking  divides IPv4 network addresses into host and network compo-       nents at byte boundaries, as follows:       Class A   This address type is indicated by the value  0  in  the  most                 significant  bit  of the (network byte ordered) address.  The                 network address is contained in the  most  significant  byte,                 and the host address occupies the remaining three bytes.       Class B   This  address type is indicated by the binary value 10 in the                 most significant two bits of the address.   The  network  ad-                 dress is contained in the two most significant bytes, and the                 host address occupies the remaining two bytes.       Class C   This address type is indicated by the binary value 110 in the                 most  significant three bits of the address.  The network ad-                 dress is contained in the three most significant  bytes,  and                 the host address occupies the remaining byte.       Classful  network addresses are now obsolete, having been superseded by       Classless Inter-Domain Routing (CIDR),  which  divides  addresses  into       network  and host components at arbitrary bit (rather than byte) bound-       aries.EXAMPLE       An example of the use of inet_aton() and inet_ntoa()  is  shown  below.       Here are some example runs:           $ ./a.out 226.000.000.037      # Last byte is in octal           226.0.0.31           $ ./a.out 0x7f.1               # First byte is in hex           127.0.0.1   Program source       #define _BSD_SOURCE       #include <arpa/inet.h>       #include <stdio.h>       #include <stdlib.h>       int       main(int argc, char *argv[])       {           struct in_addr addr;           if (argc != 2) {               fprintf(stderr, "%s <dotted-address>\n", argv[0]);               exit(EXIT_FAILURE);           }           if (inet_aton(argv[1], &addr) == 0) {               fprintf(stderr, "Invalid address\n");               exit(EXIT_FAILURE);           }           printf("%s\n", inet_ntoa(addr));           exit(EXIT_SUCCESS);       }SEE ALSObyteorder(3),getaddrinfo(3),gethostbyname(3),getnameinfo(3), getne-tent(3),inet_net_pton(3),inet_ntop(3),inet_pton(3),hosts(5),  net-works(5)COLOPHON       This  page  is  part of release 5.05 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/.GNU                               2019-03-06INET(3)