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SOCKADDR_SNPRINTF(3) NetBSD Library Functions Manual SOCKADDR_SNPRINTF(3)
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sockaddr_snprintf -- formatting function for socket address structures
System Utilities Library (libutil, -lutil)
sockaddr_snprintf(char *buf, size_t buflen, const char *fmt,
const struct sockaddr *sa);
The sockaddr_snprintf() function formats a socket address into a form
suitable for printing.
This function is convenient because it is protocol independent, i.e. one
does not need to know the address family of the sockaddr in order to
print it. The printf(3) like format string specifies how the address is
going to be printed. Some formatting characters are only supported by
some address families. If a certain formatting character is not sup-
ported, then the string ``N/A'' is printed.
The resulting formatted string is placed into buf. Up to buflen charac-
ters are placed in buf.
The following formatting characters are supported (immediately after a
percent (`%') sign):
a The node address portion of the socket address is printed numeri-
cally. For AF_INET the address is printed as: ``A.B.C.D'' and for
AF_INET6 the address is printed as: ``A:B...[%if]'' using
getnameinfo(3) internally with NI_NUMERICHOST. For AF_APPLETALK the
address is printed as: ``A.B'' For AF_LOCAL (AF_UNIX) the address is
printed as: ``socket-path'' For AF_LINK the address is printed as:
``a.b.c.d.e.f'' using link_ntoa(3), but the interface portion is
skipped (see below). For AF_UNSPEC nothing is printed.
A The symbolic name of the address is printed. For AF_INET and
AF_INET6 this is the hostname associated with the address. For all
other address families, it is the same as the ``a'' format.
D Debugging output: For all addresses, print all their fields as
f The numeric value of the family of the address is printed.
l The length of the socket address is printed.
p For AF_INET, AF_INET6, and AF_APPLETALK the numeric value of the port
portion of the address is printed.
P For AF_INET and AF_INET6 this is the name of the service associated
with the port number, if available. For all other address families,
it is the same as the ``p'' format.
I For AF_LINK addresses, the interface name portion is printed.
F For AF_INET6 addresses, the flowinfo portion of the address is
R For AF_APPLETALK addresses, the netrange portion of the address is
printed as: ``phase:[firstnet,lastnet]''
S For AF_INET6 addresses, the scope portion of the address is printed
? If present between ``%'' and the format character, and the selected
format does not apply to the given address family, the ``N/A'' string
is elided and no output results.
The sockaddr_snprintf() function returns the number of characters that
are required to format the value val given the format string fmt exclud-
ing the terminating NUL. The returned string in buf is always NUL-termi-
nated. If the address family is not supported, sockaddr_snprintf()
returns -1 and sets errno to EAFNOSUPPORT. For AF_INET and AF_INET6
addresses sockaddr_snprintf() returns -1 if the getnameinfo(3) conversion
failed, and errno is set to the error value from getnameinfo(3).
If the buffer buf is too small to hold the formatted output,
sockaddr_snprintf() will still return the buffer, containing a truncated
getaddrinfo(3), getnameinfo(3), link_ntoa(3), snprintf(3)
The sockaddr_snprintf() first appeared in NetBSD 3.0.
The sockaddr_snprintf() interface is experimental and might change in the
There is no way to specify different formatting styles for particular
addresses. For example it would be useful to print AF_LINK addresses as
``%.2x:%.2x...'' instead of ``%x.%x...''
This function is supposed to be quick, but getnameinfo(3) might use sys-
tem calls to convert the scope number to an interface name and the ``A''
and ``P'' format characters call getaddrinfo(3) which may block for a
noticeable period of time.
Not all formatting characters are supported by all address families and
printing ``N/A'' is not very convenient. The ``?'' character can sup-
press this, but other formatting (e.g., spacing or punctuation) will
NetBSD 9.2 June 7, 2013 NetBSD 9.2