| SD_ID128_TO_STRING(3) | sd_id128_to_string | SD_ID128_TO_STRING(3) |
.SH "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
.SH "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) ...
.HP 600u char
*sd_id128_to_string(sd_id128_t id, char s[static SD_ID128_STRING_MAX]);
.HP 720u char
*sd_id128_to_uuid_string(sd_id128_t id, char s[static SD_ID128_UUID_STRING_MAX]);
.HP 600u int
sd_id128_from_string(const char *s, sd_id128_t *ret);
.SH "DESCRIPTION"
.PP 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.
.PP 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.
.PP 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 hexadecimal digits and dashes,
terminated by a NUL byte.
.PP 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, and a
46-character string consisting of the 9-character urn:uuid: prefix, a
36-character RFC UUID, and a terminating NUL. If ret is passed
as NULL the function will validate the passed ID string, but not
actually return it in parsed form.
.PP 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.
.PP 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.
.PP 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).
.SH "RETURN VALUE"
.PP 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.
.SH "NOTES"
.PP Functions described here are available as a shared library, which can be
compiled against and linked to with the
libsystemd pkg-config(1) file.
.PP 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.
.SH "HISTORY"
.PP sd_id128_to_string() and sd_id128_from_string() were added
in version 187.
.PP sd_id128_to_uuid_string() was added in version 251.
.SH "SEE ALSO"
.PP systemd(1), sd-id128(3), printf(3)
NOTES
- 1.
- RFC4122
| systemd 262.2 |