sd_id128_to_string(3) — Linux manual page


SD_ID128_TO_STRING(3)      sd_id128_to_string      SD_ID128_TO_STRING(3)

NAME         top

       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         top

       #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) ...

                                *sd_id128_to_string(sd_id128_t id, char s[static SD_ID128_STRING_MAX]);

                                  *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         top

       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         top

       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         top

       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

HISTORY         top

       sd_id128_to_string() and sd_id128_from_string() were added in
       version 187.

       sd_id128_uuid_string() was added in version 251.

SEE ALSO         top

       systemd(1), sd-id128(3), printf(3)

NOTES         top

        1. RFC4122

COLOPHON         top

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systemd 255                                        SD_ID128_TO_STRING(3)

Pages that refer to this page: sd_bus_set_address(3)sd-id128(3)