text: #include <arpa/inet.h>
  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._pton()
  returns the number of bits in the network number. On error,
  it returns −1, and
  errno
  is set to indicate the error.
  On success,
  inet_net_ntop()
  returns
  pres. On
  error, it returns NULL, and
  errno is set to indicate the error.
  af specified
  a value other than
  AF_INET.
  The size of the output buffer was insufficient.
  (
  inet_net_pton())
  pres was not in
  correct presentation format.
  The
  inet_net_pton() and
  inet_net_ntop() functions are
  nonstandard, but widely available. "−l−form [addr−init−value] == −1)); }