The hsearch interface to the Berkeley DB library is intended to
provide a high-performance implementation and source code compatibility
for applications written to the historic hsearch interface.
It is not recommended for any other purpose.
To compile hsearch applications, replace the application's
#include of the hsearch include
file (e.g., #include <search.h>)
with the following two lines:
#define DB_DBM_HSEARCH 1
#include <db.h>
and recompile.
The hcreate function creates an in-memory database. The
nelem argument is an estimation of the maximum number of key/data
pairs that will be stored in the database.
The hdestroy function discards the database.
Database elements are structures of type ENTRY, which contain at
least two fields: key and data. The field key is
declared to be of type char * and is the key used for storage
and retrieval. The field data is declared to be of type
void * and is its associated data.
The hsearch function retrieves key/data pairs from, and stores
key/data pairs into the database.
The action argument must be set to one of two values:
ENTER
If the key does not already appear in the database,
insert the key/data pair into the database.
If the key already appears in the database,
return a reference to an ENTRY
structure referencing the existing key and its associated data element.
FIND
Retrieve the specified key/data pair from the database.
Compatibility Notes
Historically, hsearch required applications to maintain the keys
and data in the application's memory for as long as the hsearch
database existed. As Berkeley DB handles key and data management internally,
there is no requirement that applications maintain local copies of key
and data items, although the only effect of doing so should be the
allocation of additional memory.
Hsearch Diagnostics
The hcreate function returns 0 on failure, setting errno
and non-zero on success.
The hsearch function returns a pointer to an ENTRY structure on
success, and NULL, setting errno, if the action
specified was FIND and the item did not appear in the database.
Errors
The hcreate 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 hcreate function may fail and return
DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail
in the same way.
The hsearch 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 hsearch function may fail and return
DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail
in the same way.
In addition, the hsearch function will fail, setting errno
to 0, if the action specified was FIND and the item did not appear in
the database.