#include <db.h>

DB_ENV->set_alloc(DB_ENV *dbenv,
    void *(*app_malloc)(size_t),
    void *(*app_realloc)(void *, size_t),
    void (*app_free)(void *));  

Set the allocation functions used by the DB_ENV and DB methods to allocate or free memory owned by the application.

There are a number of interfaces in Berkeley DB where memory is allocated by the library and then given to the application. For example, the DB_DBT_MALLOC flag, when specified in the DBT object, will cause the DB methods to allocate and reallocate memory which then becomes the responsibility of the calling application. Other examples are the Berkeley DB interfaces which return statistical information to the application: DB->stat(), DB_ENV->lock_stat(), DB_ENV->log_archive(), DB_ENV->log_stat(), DB_ENV->memp_stat(), and DB_ENV->txn_stat(). There is one method in Berkeley DB where memory is allocated by the application and then given to the library: the callback specified to DB->associate().

On systems in which there may be multiple library versions of the standard allocation routines (notably Windows NT), transferring memory between the library and the application will fail because the Berkeley DB library allocates memory from a different heap than the application uses to free it. To avoid this problem, the DB_ENV->set_alloc() and DB->set_alloc() methods can be used to pass Berkeley DB references to the application's allocation routines.

It is not an error to specify only one or two of the possible allocation function parameters to these interfaces; however, in that case the specified interfaces must be compatible with the standard library interfaces, as they will be used together. The functions specified must match the calling conventions of the ANSI C X3.159-1989 (ANSI C) library routines of the same name.

The DB_ENV->set_alloc() method configures operations performed using the specified DB_ENV handle, not all operations performed on the underlying database environment.

The DB_ENV->set_alloc() method may not be called after the DB_ENV->open() method is called.

The DB_ENV->set_alloc() method returns a non-zero error value on failure and 0 on success.



The app_malloc parameter is the application-specified malloc function.


The app_realloc parameter is the application-specified realloc function.


The app_free parameter is the application-specified free function.


The DB_ENV->set_alloc() method may fail and return one of the following non-zero errors:


If the method was called after DB_ENV->open() was called; or if an invalid flag value or parameter was specified.



See Also

Database Environments and Related Methods