mongoc_client_set_read_prefs()

void
mongoc_client_set_read_prefs (mongoc_client_t           *client,
                              const mongoc_read_prefs_t *read_prefs);

Sets the default read preferences to use with future operations upon client.

The global default is to read from the replica set primary.

It is a programming error to call this function on a client from a mongoc_client_pool_t. For pooled clients, set the read preferences with the MongoDB URI instead.

Please see the MongoDB website for a description of Read Preferences.