int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb);
In brief, sqlite3_wal_checkpoint(D,X) causes the content in the write-ahead log for database X on database connection D to be transferred into the database file and for the write-ahead log to be reset. See the checkpointing documentation for addition information.
This interface used to be the only way to cause a checkpoint to occur. But then the newer and more powerful sqlite3_wal_checkpoint_v2() interface was added. This interface is retained for backwards compatibility and as a convenience for applications that need to manually start a callback but which do not need the full power (and corresponding complication) of sqlite3_wal_checkpoint_v2().