x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_ID128_TO_STRING(3) sd_id128_to_string SD_ID128_TO_STRING(3)
NAME
sd_id128_to_string, SD_ID128_TO_STRING, SD_ID128_STRING_MAX,
sd_id128_to_uuid_string, SD_ID128_TO_UUID_STRING,
SD_ID128_UUID_STRING_MAX, sd_id128_from_string - Format or parse
128-bit IDs as strings
SYNOPSIS
#include <systemd/sd-id128.h>
#define SD_ID128_STRING_MAX 33U
#define SD_ID128_UUID_STRING_MAX 37U
#define SD_ID128_TO_STRING(id) ...
#define SD_ID128_TO_UUID_STRING(id) ...
char
*sd_id128_to_string(sd_id128_t id, char s[static SD_ID128_STRING_MAX]);
char
*sd_id128_uuid_string(sd_id128_t id, char s[static SD_ID128_UUID_STRING_MAX]);
int sd_id128_from_string(const char *s, sd_id128_t *ret);
DESCRIPTION
sd_id128_to_string() formats a 128-bit ID as a character string. It
expects the ID and a string array capable of storing 33 characters
(SD_ID128_STRING_MAX). The ID will be formatted as 32 lowercase
hexadecimal digits and be terminated by a NUL byte.
SD_ID128_TO_STRING() is a macro that wraps sd_id128_to_string() and
passes an appropriately sized buffer as second argument, allocated as
C99 compound literal. Each use will thus implicitly acquire a suitable
buffer on the stack which remains valid until the end of the current
code block. This is usually the simplest way to acquire a string
representation of a 128-bit ID in a buffer that is valid in the current
code block.
sd_id128_to_uuid_string() and SD_ID128_TO_UUID_STRING() are similar to
these two functions/macros, but format the 128-bit values as RFC4122
UUIDs, i.e. a series of 36 lowercase hexadeciaml digits and dashes,
terminated by a NUL byte.
sd_id128_from_string() implements the reverse operation: it takes a 33
character string with 32 hexadecimal digits (either lowercase or
uppercase, terminated by NUL) and parses them back into a 128-bit ID
returned in ret. Alternatively, this call can also parse a 37-character
string with a 128-bit ID formatted as RFC UUID. If ret is passed as
NULL the function will validate the passed ID string, but not actually
return it in parsed form.
Note that when formatting and parsing 36 character UUIDs this is done
strictly in Big Endian byte order, i.e. according to RFC4122[1] Variant
1 rules, even if the UUID encodes a different variant. This matches
behaviour in various other Linux userspace tools. It's probably wise to
avoid UUIDs of other variant types.
For more information about the "sd_id128_t" type see sd-id128(3). Note
that these calls operate the same way on all architectures, i.e. the
results do not depend on endianness.
When formatting a 128-bit ID into a string, it is often easier to use a
format string for printf(3). This is easily done using the
SD_ID128_FORMAT_STR and SD_ID128_FORMAT_VAL() macros. For more
information see sd-id128(3).
RETURN VALUE
sd_id128_to_string() always succeeds and returns a pointer to the
string array passed in. sd_id128_from_string() returns 0 on success,
in which case ret is filled in, or a negative errno-style error code.
NOTES
Functions described here are available as a shared library, which can
be compiled against and linked to with the libsystemd pkg-config(1)
file.
The code described here uses getenv(3), which is declared to be not
multi-thread-safe. This means that the code calling the functions
described here must not call setenv(3) from a parallel thread. It is
recommended to only do calls to setenv() from an early phase of the
program when no other threads have been started.
SEE ALSO
systemd(1), sd-id128(3), printf(3)
NOTES
1. RFC4122
https://tools.ietf.org/html/rfc4122
systemd 254 SD_ID128_TO_STRING(3)
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