int DB->set_alloc(DB *db, void *(*app_malloc)(size_t size), 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. The DB_ENV->set_alloc interface sets the allocation functions for a database environment; the DB->set_alloc interface sets the allocation functions for a single database. If both are specified, functions specified for a database will be used in preference to functions specified for environment.
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. (See DBT for more information.) Other examples are the Berkeley DB interfaces which return statistical information to the application: DB->stat, lock_stat, log_archive, log_stat, memp_stat, and txn_stat. There is one interface in the Berkeley DB where memory is allocated by the application and then given to the library: 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 functions can be used to pass Berkeley DB references to the application's allocation routines.
It is not an error to not specify all three arguments 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.
For DB handles opened inside of Berkeley DB environments, calling the DB->set_alloc function affects the entire environment and is equivalent to calling the DB_ENV->set_alloc function.
The DB->set_alloc interface may be used only to configure Berkeley DB before the DB->open interface is called.
The DB->set_alloc function returns a non-zero error value on failure and 0 on success.
The DB->set_alloc function may fail and return a non-zero error for the following conditions:
The DB->set_alloc function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the DB->set_alloc function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.
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