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12 Export and Import
Gdbm
databases can be converted into a portable flat
format. This format can be used, for example, to migrate between
the different versions of gdbm
databases. Generally speaking,
flat files are safe to send over the network, and can be used to
recreate the database on another machine. The recreated database is
guaranteed to be a byte-to-byte equivalent of the database from which
the flat file was created. This does not necessarily mean, however,
that this file can be used in the same way as the original one. For
example, if the original database contained non-ASCII data
(e.g. C structures, integers etc.), the recreated database
can be of any use only if the target machine has the same integer
size and byte ordering as the source one and if its C
compiler uses the same packing conventions as the one which generated
C which populated the original database. In general, such
binary databases are not portable between machines, unless you follow
some stringent rules on what data is written to them and how it is
interpreted.
- gdbm interface: int gdbm_export (GDBM_FILE dbf, const char *exportfile, int flag, int mode)
Create a flat file from the
gdbm
database. The parameters are:- dbf
A pointer to the source database, returned by a call to
gdbm_open
. The database must be open in ‘GDBM_WRITER’ mode.- exportfile
The name of the output file.
- flag
-
How to create the output file. If flag is ‘GDBM_WRCREAT’, the file will be created if it does not exist already. Otherwise, if it is ‘GDBM_NEWDB’, it will be created if it does not exist, and truncated otherwise.
- mode
The permissions to use when creating the output file. See http://www.manpagez.com/man/2/open, for a detailed discussion.
- gdbm interface: int gdbm_import (GDBM_FILE dbf, const char *importfile, int flag)
Populates the database from an existing flat file.
- dbf
A pointer to the source database, returned by a call to
gdbm_open
. The database must be open in ‘GDBM_WRITER’ mode.- importfile
The name of the input flat file. The file must exist.
- flag
The flag argument to be passed to
gdbm_store
function when adding new records. See section Inserting and replacing records in the database., for a description of its effect.
See also Export a database into a portable format., testgdbm export, and testgdbm import.
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