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sd_id128_to_string(3) [centos man page]

SD_ID128_TO_STRING(3)						sd_id128_to_string					     SD_ID128_TO_STRING(3)

NAME
sd_id128_to_string, sd_id128_from_string - Format or parse 128-bit IDs as strings SYNOPSIS
#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); DESCRIPTION
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. NOTES
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-id128" pkg-config(1) file. SEE ALSO
systemd(1), sd-id128(3), printf(3) systemd 208 SD_ID128_TO_STRING(3)

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SD-ID128(3)							     sd-id128							       SD-ID128(3)

NAME
sd-id128, sd_id128_t, SD_ID128_MAKE, SD_ID128_CONST_STR, SD_ID128_FORMAT_STR, SD_ID128_FORMAT_VAL, sd_id128_equal - APIs for processing 128-bit IDs SYNOPSIS
#include <systemd/sd-id128.h> pkg-config --cflags --libs libsystemd-id128 DESCRIPTION
sd-id128.h provides APIs to process and generate 128-bit ID values. The 128-bit ID values processed and generated by these APIs are a generalization of OSF UUIDs as defined by RFC 4122[1] but use a simpler string format. These functions impose no structure on the used IDs, much unlike OSF UUIDs or Microsoft GUIDs, but are fully compatible with those types of IDs. See sd_id128_to_string(3), sd_id128_randomize(3) and sd_id128_get_machine(3) for more information about the implemented functions. A 128-bit ID is implemented as the following union type: typedef union sd_id128 { uint8_t bytes[16]; uint64_t qwords[2]; } sd_id128_t; This union type allows accessing the 128-bit ID as 16 separate bytes or two 64-bit words. It is generally safer to access the ID components by their 8-bit array to avoid endianness issues. This union is intended to be passed call-by-value (as opposed to call-by-reference) and may be directly manipulated by clients. A couple of macros are defined to denote and decode 128-bit IDs: SD_ID128_MAKE() may be used to denote a constant 128-bit ID in source code. A commonly used idiom is to assign a name to a 128-bit ID using this macro: #define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1) SD_ID128_CONST_STR() may be used to convert constant 128-bit IDs into constant strings for output. The following example code will output the string "fc2e22bc6ee647b6b90729ab34a250b1": int main(int argc, char *argv[]) { puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP)); } SD_ID128_FORMAT_STR and SD_ID128_FORMAT_VAL() may be used to format a 128-bit ID in a printf(3) format string, as shown in the following example: int main(int argc, char *argv[]) { sd_id128_t id; id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ". ", SD_ID128_FORMAT_VAL(id)); return 0; } Use sd_id128_equal() to compare two 128-bit IDs: int main(int argc, char *argv[]) { sd_id128_t a, b, c; a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e); c = a; assert(sd_id128_equal(a, c)); assert(!sd_id128_equal(a, b)); return 0; } Note that new, randomized IDs may be generated with journalctl(1)'s --new-id option. NOTES
These APIs are implemented as a shared library, which can be compiled and linked to with the "libsystemd-id128" pkg-config(1) file. SEE ALSO
systemd(1), sd_id128_to_string(3), sd_id128_randomize(3), sd_id128_get_machine(3), printf(3), journalctl(1), sd-journal(7), pkg-config(1), machine-id(5) NOTES
1. RFC 4122 https://tools.ietf.org/html/rfc4122 systemd 208 SD-ID128(3)

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