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106 lines
4.1 KiB
TeX
106 lines
4.1 KiB
TeX
\section{\module{gdbm} ---
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GNU's reinterpretation of dbm}
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\declaremodule{builtin}{gdbm}
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\platform{Unix}
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\modulesynopsis{GNU's reinterpretation of dbm.}
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% Note that if this section appears on the same page as the first
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% paragraph of the dbm module section, makeindex will produce the
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% warning:
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%
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% ## Warning (input = lib.idx, line = 1184; output = lib.ind, line = 852):
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% -- Conflicting entries: multiple encaps for the same page under same key.
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%
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% This is because the \bimodindex{gdbm} and \refbimodindex{gdbm}
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% entries in the .idx file are slightly different (the \bimodindex{}
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% version includes "|textbf" at the end to make the defining occurance
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% bold). There doesn't appear to be anything that can be done about
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% this; it's just a little annoying. The warning can be ignored, but
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% the index produced uses the non-bold version.
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This module is quite similar to the \refmodule{dbm}\refbimodindex{dbm}
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module, but uses \code{gdbm} instead to provide some additional
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functionality. Please note that the file formats created by
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\code{gdbm} and \code{dbm} are incompatible.
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The \module{gdbm} module provides an interface to the GNU DBM
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library. \code{gdbm} objects behave like mappings
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(dictionaries), except that keys and values are always strings.
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Printing a \code{gdbm} object doesn't print the keys and values, and
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the \method{items()} and \method{values()} methods are not supported.
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The module defines the following constant and functions:
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\begin{excdesc}{error}
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Raised on \code{gdbm}-specific errors, such as I/O errors.
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\exception{KeyError} is raised for general mapping errors like
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specifying an incorrect key.
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\end{excdesc}
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\begin{funcdesc}{open}{filename, \optional{flag, \optional{mode}}}
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Open a \code{gdbm} database and return a \code{gdbm} object. The
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\var{filename} argument is the name of the database file.
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The optional \var{flag} argument can be
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\code{'r'} (to open an existing database for reading only --- default),
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\code{'w'} (to open an existing database for reading and writing),
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\code{'c'} (which creates the database if it doesn't exist), or
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\code{'n'} (which always creates a new empty database).
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Appending \character{f} to the flag opens the database in fast mode;
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altered data will not automatically be written to the disk after every
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change. This results in faster writes to the database, but may result
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in an inconsistent database if the program crashes while the database
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is still open. Use the \method{sync()} method to force any unwritten
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data to be written to the disk.
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The optional \var{mode} argument is the \UNIX{} mode of the file, used
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only when the database has to be created. It defaults to octal
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\code{0666}.
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\end{funcdesc}
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In addition to the dictionary-like methods, \code{gdbm} objects have the
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following methods:
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\begin{funcdesc}{firstkey}{}
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It's possible to loop over every key in the database using this method
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and the \method{nextkey()} method. The traversal is ordered by
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\code{gdbm}'s internal hash values, and won't be sorted by the key
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values. This method returns the starting key.
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\end{funcdesc}
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\begin{funcdesc}{nextkey}{key}
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Returns the key that follows \var{key} in the traversal. The
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following code prints every key in the database \code{db}, without
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having to create a list in memory that contains them all:
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\begin{verbatim}
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k = db.firstkey()
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while k != None:
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print k
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k = db.nextkey(k)
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\end{verbatim}
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\end{funcdesc}
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\begin{funcdesc}{reorganize}{}
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If you have carried out a lot of deletions and would like to shrink
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the space used by the \code{gdbm} file, this routine will reorganize
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the database. \code{gdbm} will not shorten the length of a database
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file except by using this reorganization; otherwise, deleted file
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space will be kept and reused as new (key, value) pairs are added.
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\end{funcdesc}
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\begin{funcdesc}{sync}{}
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When the database has been opened in fast mode, this method forces any
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unwritten data to be written to the disk.
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\end{funcdesc}
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\begin{seealso}
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\seemodule{anydbm}{Generic interface to \code{dbm}-style databases.}
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\seemodule{whichdb}{Utility module used to determine the type of an
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existing database.}
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\end{seealso}
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