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hsearch
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<pre>
#define DB_DBM_HSEARCH 1
#include &lt;db.h&gt;

typedef enum {
 FIND, ENTER
} ACTION;

typedef struct entry {
 char *key;
 void *data;
} ENTRY;

ENTRY *
hsearch(ENTRY item, ACTION action);

int
hcreate(size_t nelem);

void
hdestroy(void);
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Description: hsearch
The hsearch functions are 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 (for example, #include &lt;search.h&gt;)
with the following two lines:
<blockquote><pre>#define DB_DBM_HSEARCH 1
#include &lt;db.h&gt;</pre></blockquote>
and recompile.
The hcreate function creates an in-memory database. The
nelem parameter 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 parameter must be set to one of two values:
 
ENTER<ul compact><li>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 which refers to the
existing key and its associated data element.</ul>
FIND<ul compact><li>Retrieve the specified key/data pair from the database.</ul>
 
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. Because 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 hsearch function will fail, setting errno to 0,
if the action specified was FIND and the item did not appear in
the database.
In addition, the hcreate, hsearch and hdestroy functions may fail and
return an error for errors specified for other Berkeley DB and C library or
system functions.
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