Format or parse 128-bit ids as strings
char *sd_id128_to_string(sd_id128_t id, char s); 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. The ID will be formatted as 32 lowercase hexadecimal digits and be 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.
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.
The sd_id128_to_string() and sd_id128_from_string() interfaces are available as a shared library, which can be compiled and linked to with the "libsystemd" pkg-config(1) file.