VSNPRINTF(9) Basic C Library Functions VSNPRINTF(9)NAME
vsnprintf - Format a string and place it in a buffer
SYNOPSIS
int vsnprintf(char * buf, size_t size, const char * fmt, va_list args);
ARGUMENTS
buf
The buffer to place the result into
size
The size of the buffer, including the trailing null space
fmt
The format string to use
args
Arguments for the format string
DESCRIPTION
This function follows C99 vsnprintf, but has some extensions: pS output the name of a text symbol with offset ps output the name of a text
symbol without offset pF output the name of a function pointer with its offset pf output the name of a function pointer without its offset
pB output the name of a backtrace symbol with its offset pR output the address range in a struct resource with decoded flags pr output the
address range in a struct resource with raw flags pM output a 6-byte MAC address with colons pMR output a 6-byte MAC address with colons in
reversed order pMF output a 6-byte MAC address with dashes pm output a 6-byte MAC address without colons pmR output a 6-byte MAC address
without colons in reversed order pI4 print an IPv4 address without leading zeros pi4 print an IPv4 address with leading zeros pI6 print an
IPv6 address with colons pi6 print an IPv6 address without colons pI6c print an IPv6 address as specified by RFC 5952 pIS depending on
sa_family of 'struct sockaddr *' print IPv4/IPv6 address piS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address pU[bBlL]
print a UUID/GUID in big or little endian using lower or upper case. %*ph[CDN] a variable-length hex string with a separator (supports up
to 64 bytes of the input) pc print a cpumask as comma-separated list n is ignored
** Please update Documentation/printk-formats.txt when making changes **
The return value is the number of characters which would be generated for the given input, excluding the trailing ' ', as per ISO C99. If
you want to have the exact number of characters written into buf as return value (not including the trailing ' '), use vscnprintf. If the
return is greater than or equal to size, the resulting string is truncated.
If you're not already dealing with a va_list consider using snprintf.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 VSNPRINTF(9)
Check Out this Related Man Page
inet6(3N)inet6(3N)NAME
inet_pton(), inet_ntop() - Internet address manipulation routines for IP Version 4 and later
SYNOPSIS DESCRIPTION
The functions and are new with IP Version 6 (IPv6) and work with both IP Version 4 (IPv4) and IPv6 addresses. The letters "p" and "n" stand
for and The presentation format for an address is often an ASCII string and the numeric format is the binary value that goes into a socket
address structure.
The ASCII string is either the IPv4 address in dot notation or an IPv6 address in colon notation. An example of an ASCII string is or
The binary value is the hex representation of the IPv4/IPv6 address. This binary value resides in the structure for IPv4 address and in the
structure for IPv6 address. (Refer to the inet(3N) manpage for more details.)
The functions and are opposite of each other. The function converts an ASCII address string to binary address, and the function converts a
binary address into ASCII address string. Also, these are equivalent to and respectively.
The inet_pton() Function
The function converts an address in its standard text presentation form into its numeric binary form.
The af argument specifies the family of the address. Currently, the and address families are supported.
The src argument points to the IPv6/IPv4 address string being passed in.
The argument points to a buffer in which the function stores the numeric address. The address is returned in network byte order.
returns if the conversion succeeds, if the input is not a valid IPv4 dotted-decimal string or a valid IPv6 address string, or with errno
set to if the af argument is unknown.
The calling application must ensure that the buffer referred to by dst is large enough to hold the numeric address (e.g., 4 bytes for or 16
bytes for
If the af argument is the function accepts a string in the standard IPv4 dotted-decimal form:
ddd.ddd.ddd.ddd
where ddd is a one to three digit decimal number between 0 and 255. Note that many implementations of the existing and functions accept
nonstandard input: octal numbers, hexadecimal numbers, and fewer than four numbers. does not accept these formats.
If the af argument is then the function accepts a string in one of the standard IPv6 text forms. (Refer to the IPv6 address notation below
for more details).
The inet_ntop() Function
The function converts a numeric address into a text string suitable for presentation.
The af argument specifies the family of the address. This can be or
The src argument points to a buffer holding an IPv4 address if the af argument is or an IPv6 address if the af argument is
The dst argument points to a buffer where the function will store the resulting text string.
The size argument specifies the size of this buffer. The application must specify a non-NULL dst argument. For IPv6 addresses, the buffer
must be at least 46-octets. For IPv4 addresses, the buffer must be at least 16-octets. In order to allow applications to easily declare
buffers of the proper size to store IPv4 and IPv6 addresses in string form, the following two constants are defined in
The function returns a pointer to the buffer containing the text string if the conversion succeeds, and NULL otherwise. Upon failure, errno
is set to if the af argument is invalid, or if the size of the result buffer is inadequate.
IPv6 Address Notation
The IPv6 address is bytes long. Example of an IPv6 address is as shown below:
The 128 bits are written as eight 16-bit integers separated by colons. Each integer is represented by four hexadecimal digits.
In the initial stages all the 128 bits will not be used, hence, it is very likely that there will be many zeros. Hence the IP address in
such a scenario will look like this:
The above address can be represented in a compact fashion, by replacing a set of consecutive null 16-bit numbers by two colons. The above
address can now be re-written as follows:
Expanding the abbreviation is very simple. Align whatever is at the left of the double colon to the left of the address: these are the
leading 16-bit words. Then align whatever is at the right of the colons to the right of the address and fill up with zeros.
The double-colon convention can be used only once inside an address.
To support the transition from IPv4, two special IPv6 addresses are supported. They are addresses and addresses.
IPv4-Compatible Addresses Description and Example
IPv4-compatible addresses can be converted to and from the older IPv4 network address format. They are used when IPv6 systems need to com-
municate with each other, but are separated by an IPv4 network.
IPv4-compatible addresses are formed by prepending 96 bits of zero, to a valid, 32-bit IPv4 address. For example, the IPv4 address of
can be converted to the IPv6 address by first converting each decimal number separated by dots (".") to a 2-digit hexadecimal value, and
concatenate into 4-digit hex values between colons (":") as listed below.
In addition, leading zeros may be omitted for each hex number between the colons. Therefore, this may be written as the following IPv6
address:
We can retain the dot-decimal format and re-write the above address as
The above address is also a valid IPv4-compatible IPv6 address.
IPv4-Mapped Addresses Description and Example
IPv4-mapped addresses indicate systems that do not support IPv6. They are limited to IPv4. An IPv6 host can communicate with an IPv4-only
host using the IPv4-mapped IPv6 address.
IPv4-mapped addresses are formed by prepending 80 bits of zero, and 16 bits of one's, to a valid 32 bit IPv4 address. An IPv4 address of
when mapped to IPv6, it becomes:
or
AUTHOR
These routines were developed by the University of California, Berkeley.
SEE ALSO gethostent(3N), getnetent(3N), inet(3N), hosts(4), networks(4).
inet6(3N)