#include <db.h> int db_env_set_func_ftruncate(int (*func_ftruncate)(int fd, off_t offset));
The Berkeley DB library requires the ability to truncate a file.
The db_env_set_func_ftruncate 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_ftruncate 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_ftruncate()
function returns a non-zero error value on failure and 0 on success.
The func_ftruncate parameter is the function which truncates a file.
The fd parameter is an open file descriptor on the file.
The ftruncate function must truncate the file to the byte length specified by the offset parameter.
The func_ftruncate function must return the value of errno on failure and 0 on success.