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UUID Generator (uuid)

Generate UUID strings conforming to RFC 4122 version 4.

Format​

xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
  • Version number is fixed to 4 (first character of the third segment), indicating random generation
  • Variant identifier y is one of 8, 9, a, b (first character of the fourth segment), conforming to RFC 4122 variant specification
  • Remaining characters are random hexadecimal digits, totaling 36 characters (including 4 hyphens)

Example: f47ac10b-58cc-4372-a567-0e02b2c3d479

API​

const char * uuid4(char * buf);

Generate and return a UUID v4 string pointer.

  • If buf is NULL, an internal static buffer is used; each call overwrites the previous result
  • If buf is non-NULL, the UUID is written into the user-provided buffer (at least 37 bytes), and the result can be safely retained

When buf is NULL, the function is not thread-safe; do not call concurrently from multiple threads.

Usage Examples​

Generating a Unique Identifier​

const char * id = uuid4(NULL);
/* id points to an internal static buffer; will be invalidated on next call */

Retaining the UUID Value​

char buf[37];
const char * id = uuid4(buf);
/* buf holds the UUID value and can be safely retained */

Dynamic String Storage​

struct ds_t * ds = ds_alloc();
ds_copy(ds, "%s", uuid4(NULL));
/* ds holds the UUID value, unaffected by subsequent uuid4 calls */
ds_free(ds);