#include <db.h> int db_env_set_func_exists(int (*func_exists)(const char *path, int *isdirp));
The Berkeley DB library requires the ability to determine whether a file exists and whether it is a file of type directory.
The db_env_set_func_exists() function configures all operations performed
by a process and all of its threads of control, not operations
confined to a single database environment.
Although the db_env_set_func_exists() function may be called at any time
during the life of the application, it should normally be called
before making calls to the db_env_create or
db_create methods.
The db_env_set_func_exists()
function returns a non-zero error value on failure and 0 on success.
The func_exists parameter is the function which returns if a file exists and if it is a file of type directory.
The path parameter to this function is the pathname of the file to be checked.
If the isdirp parameter is non-NULL, it must be set to non-0 if path is a directory, and 0 if path is not a directory.
The func_exists function must return the value of errno on failure and 0 on success.