typedef struct sqlite3_value sqlite3_value;
SQLite uses the sqlite3_value object to represent all values that can be stored in a database table. SQLite uses dynamic typing for the values it stores. Values stored in sqlite3_value objects can be integers, floating point values, strings, BLOBs, or NULL.
An sqlite3_value object may be either "protected" or "unprotected". Some interfaces require a protected sqlite3_value. Other interfaces will accept either a protected or an unprotected sqlite3_value. Every interface that accepts sqlite3_value arguments specifies whether or not it requires a protected sqlite3_value. The sqlite3_value_dup() interface can be used to construct a new protected sqlite3_value from an unprotected sqlite3_value.
The terms "protected" and "unprotected" refer to whether or not a mutex is held. An internal mutex is held for a protected sqlite3_value object but no mutex is held for an unprotected sqlite3_value object. If SQLite is compiled to be single-threaded (with SQLITE_THREADSAFE=0 and with sqlite3_threadsafe() returning 0) or if SQLite is run in one of reduced mutex modes SQLITE_CONFIG_SINGLETHREAD or SQLITE_CONFIG_MULTITHREAD then there is no distinction between protected and unprotected sqlite3_value objects and they can be used interchangeably. However, for maximum code portability it is recommended that applications still make the distinction between protected and unprotected sqlite3_value objects even when not strictly required.
The sqlite3_value objects that are passed as parameters into the implementation of application-defined SQL functions are protected. The sqlite3_value object returned by sqlite3_column_value() is unprotected. Unprotected sqlite3_value objects may only be used as arguments to sqlite3_result_value(), sqlite3_bind_value(), and sqlite3_value_dup(). The sqlite3_value_type() family of interfaces require protected sqlite3_value objects.
See also lists of Objects, Constants, and Functions.
SQLite is in the Public Domain.
https://sqlite.org/c3ref/value.html