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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |HISTORY |SEE ALSO |NOTES |COLOPHON | |
SD_ID128_TO_STRING(3) sd_id128_to_stringSD_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_tid, chars[static SD_ID128_STRING_MAX]);char*sd_id128_to_uuid_string(sd_id128_tid, chars[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 aNULbyte.SD_ID128_TO_STRING()is a macro that wrapssd_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()andSD_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 aNULbyte.sd_id128_from_string()implements the reverse operation: it takes a 33 character string with 32 hexadecimal digits (either lowercase or uppercase, terminated byNUL) and parses them back into a 128-bit ID returned inret. Alternatively, this call can also parse a 37-character string with a 128-bit ID formatted as RFC UUID. Ifret is passed asNULLthe 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 toRFC4122[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 seesd-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 forprintf(3). This is easily done using theSD_ID128_FORMAT_STRandSD_ID128_FORMAT_VAL()macros. For more information seesd-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 caseret 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 thelibsystemd pkg-config(1) file. The code described here usesgetenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not callsetenv(3) from a parallel thread. It is recommended to only do calls tosetenv()from an early phase of the program when no other threads have been started.
sd_id128_to_string()andsd_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. RFC4122https://tools.ietf.org/html/rfc4122
This page is part of thesystemd (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 isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_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)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |