1SD_ID128_TO_STRING(3)         sd_id128_to_string         SD_ID128_TO_STRING(3)
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NAME

6       sd_id128_to_string, SD_ID128_TO_STRING, SD_ID128_STRING_MAX,
7       sd_id128_to_uuid_string, SD_ID128_TO_UUID_STRING,
8       SD_ID128_UUID_STRING_MAX, sd_id128_from_string - Format or parse
9       128-bit IDs as strings
10

SYNOPSIS

12       #include <systemd/sd-id128.h>
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14       #define SD_ID128_STRING_MAX 33U
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16       #define SD_ID128_UUID_STRING_MAX 37U
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18       #define SD_ID128_TO_STRING(id) ...
19
20       #define SD_ID128_TO_UUID_STRING(id) ...
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22       char
23                                *sd_id128_to_string(sd_id128_t id, char s[static SD_ID128_STRING_MAX]);
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25       char
26                                  *sd_id128_uuid_string(sd_id128_t id, char s[static SD_ID128_UUID_STRING_MAX]);
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28       int sd_id128_from_string(const char *s, sd_id128_t *ret);
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DESCRIPTION

31       sd_id128_to_string() formats a 128-bit ID as a character string. It
32       expects the ID and a string array capable of storing 33 characters
33       (SD_ID128_STRING_MAX). The ID will be formatted as 32 lowercase
34       hexadecimal digits and be terminated by a NUL byte.
35
36       SD_ID128_TO_STRING() is a macro that wraps sd_id128_to_string() and
37       passes an appropriately sized buffer as second argument, allocated as
38       C99 compound literal. Each use will thus implicitly acquire a suitable
39       buffer on the stack which remains valid until the end of the current
40       code block. This is usually the simplest way to acquire a string
41       representation of a 128-bit ID in a buffer that is valid in the current
42       code block.
43
44       sd_id128_to_uuid_string() and SD_ID128_TO_UUID_STRING() are similar to
45       these two functions/macros, but format the 128bit values as RFC4122
46       UUIDs, i.e. a series of 36 lowercase hexadeciaml digits and dashes,
47       terminated by a NUL byte.
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49       sd_id128_from_string() implements the reverse operation: it takes a 33
50       character string with 32 hexadecimal digits (either lowercase or
51       uppercase, terminated by NUL) and parses them back into a 128-bit ID
52       returned in ret. Alternatively, this call can also parse a 37-character
53       string with a 128-bit ID formatted as RFC UUID. If ret is passed as
54       NULL the function will validate the passed ID string, but not actually
55       return it in parsed form.
56
57       Note that when formatting and parsing 36 character UUIDs this is done
58       strictly in Big Endian byte order, i.e. according to RFC4122[1] Variant
59       1 rules, even if the UUID encodes a different variant. This matches
60       behaviour in various other Linux userspace tools. It's probably wise to
61       avoid UUIDs of other variant types.
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63       For more information about the "sd_id128_t" type see sd-id128(3). Note
64       that these calls operate the same way on all architectures, i.e. the
65       results do not depend on endianness.
66
67       When formatting a 128-bit ID into a string, it is often easier to use a
68       format string for printf(3). This is easily done using the
69       SD_ID128_FORMAT_STR and SD_ID128_FORMAT_VAL() macros. For more
70       information see sd-id128(3).
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RETURN VALUE

73       sd_id128_to_string() always succeeds and returns a pointer to the
74       string array passed in.  sd_id128_from_string() returns 0 on success,
75       in which case ret is filled in, or a negative errno-style error code.
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NOTES

78       These APIs are implemented as a shared library, which can be compiled
79       and linked to with the libsystemd pkg-config(1) file.
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SEE ALSO

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

85        1. RFC4122
86           https://tools.ietf.org/html/rfc4122
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90systemd 251                                              SD_ID128_TO_STRING(3)