#include <cstdio>

 #include <sqlite3ext.h>

 #include <unistd.h>

 /**

  * This is just an example – use official documentation: https://www.sqlite.org/loadext.html

  */

 #define C_API extern "C"

 #define SQL_FN(functionName) void functionName (sqlite3_context* ctx, int valueCount, sqlite3_value** values)

 SQLITE_EXTENSION_INIT1

 /**

  * Returns number of values passed to the SQL function.

  */

 SQL_FN(valueCount) {

 	sqlite3_result_int(ctx, valueCount);

 }

 /**

  * Returns current PID (process id).

  */

 SQL_FN(getPID) {

 	sqlite3_result_int(ctx, getpid());

 }

 /**

  * Returns multiplication of all arguments or zero, if there are no arguments.

  */

 SQL_FN(multiply) {

 	sqlite3_int64 result = valueCount == 0 ? 0 : 1;

 	for (int i = 0; i < valueCount; i++) result *= sqlite3_value_int64(values[i]);

 	sqlite3_result_int64(ctx, result);

 }

 /**

  * Function name should match the library file name: libdemo.so → sqlite3_demo_init.

  * Or we can specify different entry point when loading the module.

  */

 C_API int sqlite3_demo_init(sqlite3* db, char** error, const sqlite3_api_routines* api) {

 	SQLITE_EXTENSION_INIT2(api);

 	sqlite3_create_function(db, "value_count", -1, SQLITE_UTF8, nullptr, valueCount, nullptr, nullptr);

 	sqlite3_create_function(db, "get_pid", 0, SQLITE_UTF8, nullptr, getPID, nullptr, nullptr);

 	sqlite3_create_function(db, "multiply", -1, SQLITE_UTF8, nullptr, multiply, nullptr, nullptr);

 	// -1 = function accepts arbitrary number of arguments

 	return SQLITE_OK;

 }