MySQL 8.4 C API Developer Guide / ... / C API Basic Interface / C API Basic Function Descriptions / mysql_select_db()
intmysql_select_db(MYSQL *mysql, const char *db) Causes the database specified bydb to become the default (current) database on the connection specified bymysql. In subsequent queries, this database is the default for table references that include no explicit database specifier.
mysql_select_db() fails unless the connected user can be authenticated as having permission to use the database or some object within it.
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.