sd_id128_to_string man page

sd_id128_to_string, sd_id128_from_string — Format or parse 128-bit IDs as strings


#include <systemd/sd-id128.h>

char *sd_id128_to_string(sd_id128_t id, char s[33]);
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).

Return Value

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.

See Also

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

Referenced By

sd-id128(3), systemd.directives(7), systemd.index(7).

Explore man page connections for sd_id128_to_string(3).

sd_id128_from_string(3) is an alias of sd_id128_to_string(3).