7 Searching for records in the database

gdbm interface: datum gdbm_fetch (GDBM_FILE dbf, datum key) ¶

Looks up a given key and returns the information associated with it. The dptr field in the structure that is returned points to a memory block allocated by malloc. It is the caller’s responsibility to free it when no longer needed.

If the dptr is NULL, inspect the value of the gdbm_errno variable (see gdbm_errno). If it is GDBM_ITEM_NOT_FOUND, no data was found. Any other value means an error occurred. Use gdbm_strerror function to convert gdbm_errno to a human-readable string.

The parameters are:

dbf

The pointer returned by gdbm_open.

key

The search key.

An example of using this function:

content = gdbm_fetch (dbf, key);
if (content.dptr == NULL)
  {
    if (gdbm_errno == GDBM_ITEM_NOT_FOUND)
      fprintf(stderr, "key not found\n");
    else
      fprintf(stderr, "error: %s\n", gdbm_db_strerror (dbf));
  }
else
  {
    /* do something with content.dptr */
  }

You may also search for a particular key without retrieving it:

gdbm interface: int gdbm_exists (GDBM_FILE dbf, datum key) ¶

Checks whether the key exists in the database dbf.

If key is found, returns true (1). If it is not found, returns false (0) and sets gdbm_errno to GDBM_NO_ERROR (0).

On error, returns 0 and sets gdbm_errno to a non-0 error code.

The parameters are:

dbf

The pointer returned by gdbm_open.

key

The search key.