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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SD_ID128_TO_STRING(3) sd_id128_to_string SD_ID128_TO_STRING(3)
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
#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_to_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);
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).
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.
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.
sd_id128_to_string() and sd_id128_from_string() were added in
version 187.
sd_id128_to_uuid_string() was added in version 251.
systemd(1), sd-id128(3), printf(3)
1. RFC4122
https://tools.ietf.org/html/rfc4122
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_ID128_TO_STRING(3)
Pages that refer to this page: sd_bus_set_address(3), sd-id128(3), systemd.network(5), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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