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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



 NAME
      GDBM - The GNU database manager.  Includes dbm and ndbm compatibility.

 SYNOPSIS
      #include <gdbm.h>

      extern gdbm_error gdbm_errno;
      extern char *gdbm_version;
      GDBM_FILE gdbm_open (const char *name, int block_size,
                           int flags, int mode,
                           void (*fatal_func)(const char *));
      void gdbm_close (GDBM_FILE dbf);
      int gdbm_store (GDBM_FILE dbf, datum key, datum content
      datum gdbm_fetch (GDBM_FILE dbf, datum key);
      int gdbm_delete (GDBM_FILE dbf, datum key);
      datum gdbm_firstkey (GDBM_FILE dbf);
      datum gdbm_nextkey (GDBM_FILE dbf, datum key);
      int gdbm_reorganize (GDBM_FILE dbf);
      void gdbm_sync (GDBM_FILE dbf);
      int gdbm_exists (GDBM_FILE dbf, datum key);
      const char *gdbm_strerror (gdbm_error errno);
      int gdbm_setopt (GDBM_FILE dbf, int option, int value
      int gdbm_fdesc (GDBM_FILE dbf);

    DBM Compatibility routines:
      #include <dbm.h>

      int dbminit (const char *name);
      int store (datum key, datum content);
      datum fetch (datum key);
      int delete (datum key);
      datum firstkey (void);
      datum nextkey (datum key);
      int dbmclose (void);

    NDBM Compatibility routines:
      #include <ndbm.h>

      DBM *dbm_open (const char *name, int flags, int mode
      void dbm_close (DBM *file); datumdbm_fetch(DBM* file , datum
      int dbm_store (DBM *file, datum key, datum content
      int dbm_delete (DBM *file, datum key);
      datum dbm_firstkey (DBM *file);
      datum dbm_nextkey (DBM *file, datum key);
      int dbm_error (DBM *file);
      int dbm_clearerr (DBM *file);
      int dbm_pagfno (DBM *file);
      int dbm_dirfno (DBM *file);
      int dbm_rdonly (DBM *file);



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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



 DESCRIPTION
      GNU dbm is a library of routines that manages data files that contain
      key/data pairs.  The access provided is that of storing, retrieval,
      and deletion by key and a non-sorted traversal of all keys.  A process
      is allowed to use multiple data files at the same time.

      This manpage is a short description of the GDBM library.  For a
      detailed discussion, including examples of the configuration and usage
      recommendations, refer to the GDBM Manual available in Texinfo format.
      To access it, run:

        info gdbm

      Should any discrepancies occur between this manpage and the GDBM
      Manual, the later shall be considered the authoritative source.

      A process that opens a gdbm file is designated as a "reader" or a
      "writer".  Only one writer may open a gdbm file and many readers may
      open the file.  Readers and writers can not open the gdbm file at the
      same time. The procedure for opening a gdbm file is:

      GDBM_FILE gdbm_open (const char *name, int block_size,
                           int flags, int mode,
                           void (*fatal_func)(const char *));

      Name is the name of the file (the complete name, gdbm does not append
      any characters to this name).  Block_size is the size of a single
      transfer from disk to memory. This parameter is ignored unless the
      file is a new file.  The minimum size is 512.  If it is less than 512,
      dbm will use the stat block size for the file system.  Read_write can
      have one of the following values:

      GDBM_READER
           reader

      GDBM_WRITER
           writer

      GDBM_WRCREAT
           writer - if database does not exist create new one

      GDBM_NEWDB
           writer - create new database regardless if one exists

      The GDBM_NOMMAP added to read_write by bitwise or instructs gdbm_open
      to disable the use of mmap(2).

      For the last three (writers of the database) the following may be
      added added to read_write by bitwise or:



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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



      GDBM_SYNC
           Causes all database operations to be synchronized to the disk,

      GDBM_NOLOCK
           Prevents the library from performing any locking on the database
           file.

      The option GDBM_FAST is now obsolete, since gdbm defaults to no-sync
      mode.

      Mode is the file mode (see chmod(2) and open(2)) if the file is
      created. (*Fatal_func) () is a function for dbm to call if it detects
      a fatal error. The only parameter of this function is a string.  If
      the value of 0 is provided, gdbm will use a default function.

      The return value is the pointer needed by all other routines to access
      that gdbm file.  If the return is the NULL pointer, gdbm_open was not
      successful.  The errors can be found in gdbm_errno for gdbm errors and
      in errno for system errors.  (For error codes, see gdbmerrno.h.)

      In all of the following calls, the parameter dbf refers to the pointer
      returned from gdbm_open.

      It is important that every file opened is also closed.  This is needed
      to update the reader/writer count on the file.  This is done by:

      void gdbm_close (GDBM_FILE dbf);

      The database is used by 3 primary routines.  The first stores data in
      the database.

      int gdbm_store (GDBM_FILE dbf, datum key, datum content

      Dbf is the pointer returned by gdbm_open.  Key is the key data.
      Content is the data to be associated with the key.  Flag can have one
      of the following values:

      GDBM_INSERT
           Insert only, generate an error if key exists;

      GDBM_REPLACE
           Replace contents if key exists.

      If a reader calls gdbm_store, the return value will be  -1.  If called
      with GDBM_INSERT and key is in the database, the return value will be
      1.  Otherwise, the return value is 0.

      NOTICE: If you store data for a key that is already in the data base,
      gdbm replaces the old data with the new data if called with



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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



      GDBM_REPLACE.  You do not get two data items for the same key and you
      do not get an error from gdbm_store.

      NOTICE: The size in gdbm is not restricted like in dbm or ndbm.  Your
      data can be as large as you want.

      To search for some data, use:

      datum gdbm_fetch (GDBM_FILE dbf, datum key);

      Dbf is the pointer returned by gdbm_open.  Key is the key data.

      If the dptr element of the return value is NULL, the gdbm_errno
      variable should be examined.  The value of GDBM_ITEM_NOT_FOUND means
      no data was found for that key.  Other value means an error occurred.

      Otherwise the return value is a pointer to the found data.  The
      storage space for the dptr element is allocated using malloc(3).  Gdbm
      does not automatically free this data.  It is the programmer's
      responsibility to free this storage when it is no longer needed.

      To search for some data, without retrieving it:

      int gdbm_exists (GDBM_FILE dbf, datum key);

      Dbf is the pointer returned by gdbm_open.  Key is the key data to
      search for.

      If the key is found within the database, the return value will be
      true.  If nothing appropriate is found, false is returned.  This
      routine is useful for checking for the existence of a record, without
      performing the memory allocation done by gdbm_fetch.

      To remove some data from the database:

      int gdbm_delete (GDBM_FILE dbf, datum key);

      Dbf is the pointer returned by gdbm_open.  Key is the key data.

      The return value is -1 if the item is not present or the requester is
      a reader.  The return value is 0 if there was a successful delete.

      The next two routines allow for accessing all items in the database.
      This access is not key sequential, but it is guaranteed to visit every
      key in the database once.  (The order has to do with the hash values.)

      datum gdbm_firstkey (GDBM_FILE dbf);
      datum gdbm_nextkey (GDBM_FILE dbf, datum key);




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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



      Dbf is the pointer returned by gdbm_open. Key is the key data.

      The return values are both of type datum.  If the dptr element of the
      return value is NULL, inspect the gdbm_errno.  If it is
      GDBM_ITEM_NOT_FOUND, there is no first key or next key.  Otherwise, an
      error occurred.

      Again, notice that dptr points to data allocated by malloc(3) and gdbm
      will not free it for you.

      These functions were intended to visit the database in read-only
      algorithms, for instance, to validate the database or similar
      operations.

      File `visiting' is based on a `hash table'.  gdbm_delete re-arranges
      the hash table to make sure that any collisions in the table do not
      leave some item `un-findable'.  The original key order is NOT
      guaranteed to remain unchanged in ALL instances.  It is possible that
      some key will not be visited if a loop like the following is executed:

           key = gdbm_firstkey (dbf);
           while (key.dptr)
             {
               nextkey = gdbm_nextkey (dbf, key);
               if (some condition)
                 gdbm_delete ( dbf, key );
               free (key.dptr);
               key = nextkey;
             }

      The following routine should be used very infrequently.

      int gdbm_reorganize (GDBM_FILE dbf);

      If you have had a lot of deletions and would like to shrink the space
      used by the gdbm file, this routine will reorganize the database.
      Gdbm will not shorten the length of a gdbm file except by using this
      reorganization.  (Deleted file space will be reused.)

      Unless your database was opened with the GDBM_SYNC flag, gdbm does not
      wait for writes to be flushed to the disk before continuing.  The
      following routine can be used to guarantee that the database is
      physically written to the disk file.

      void gdbm_sync (GDBM_FILE dbf);

      It will not return until the disk file state is syncronized with the
      in-memory state of the database.




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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



      To convert a gdbm error code into English text, use this routine:

      const char *gdbm_strerror (gdbm_error errno);

      Gdbm now supports the ability to set certain options on an already
      open database.

      int gdbm_setopt (GDBM_FILE dbf, int option, int value

      Where dbf is the return value from a previous call to gdbm_open, and
      option specifies which option to set.  The valid options are
      currently:

      GDBM_CACHESIZE
           Set the size of the internal bucket cache. This option may only
           be set once on each GDBM_FILE descriptor, and is set
           automatically to 100 upon the first access to the database.

      GDBM_FASTMODE
            Set fast mode to either on or off.  This allows fast mode to be
           toggled on an already open and active database. value (see below)
           should be set to either TRUE or FALSE.  This option is now
           obsolete.

      GDBM_SYNCMODE
           Turn on or off file system synchronization operations.  This
           setting defaults to off; value (see below) should be set to
           either TRUE or FALSE.

      GDBM_CENTFREE
           Set central free block pool to either on or off.  The default is
           off, which is how previous versions of Gdbm handled free blocks.
           If set, this option causes all subsequent free blocks to be
           placed in the global pool, allowing (in thoery) more file space
           to be reused more quickly. value (see below) should be set to
           either TRUE or FALSE.  NOTICE: This feature is still under study.

      GDBM_COALESCEBLKS
           Set free block merging to either on or off.  The default is off,
           which is how previous versions of Gdbm handled free blocks. If
           set, this option causes adjacent free blocks to be merged.  This
           can become a CPU expensive process with time, though, especially
           if used in conjunction with GDBM_CENTFREE. value (see below)
           should be set to either TRUE or FALSE.  NOTICE: This feature is
           still under study.

      value is the value to set option to, specified as an integer pointer.
      size is the size of the data pointed to by value.  The return value
      will be -1 upon failure, or 0 upon success.  The global variable



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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



      gdbm_errno will be set upon failure.

      For instance, to set a database to use a cache of 10, after opening it
      with gdbm_open, but prior to accessing it in any way, the following
      code could be used:

           int value = 10;

           ret = gdbm_setopt( dbf, GDBM_CACHESIZE, &value, sizeof(int));

      If the database was opened with the GDBM_NOLOCK flag, the user may
      wish to perform their own file locking on the database file in order
      to prevent multiple writers operating on the same file simultaneously.

      In order to support this, the gdbm_fdesc routine is provided.

      int gdbm_fdesc (GDBM_FILE dbf);

      Where dbf is the return value from a previous call to gdbm_open.  The
      return value will be the file descriptor of the database.

      The following two external variables may be useful:

      gdbm_errno is the variable that contains more information about gdbm
      errors.  (gdbm.h has the definitions of the error values and defines
      gdbm_errno as an external variable.)

      gdbm_version is the string containing the version information.

      There are a few more things of interest.  First, gdbm files are not
      "sparse".  You can copy them with the UNIX cp(1) command and they will
      not expand in the copying process.  Also, there is a compatibility
      mode for use with programs that already use UNIX dbm.  In this
      compatibility mode, no gdbm file pointer is required by the
      programmer, and only one file may be opened at a time.  All users in
      compatibility mode are assumed to be writers.  If the gdbm file is a
      read only, it will fail as a writer, but will also try to open it as a
      reader.  All returned pointers in datum structures point to data that
      gdbm WILL free.  They should be treated as static pointers (as
      standard UNIX dbm does).

 LINKING
      This library is accessed by specifying -lgdbm as the last parameter to
      the compile line, e.g.:

           gcc -o prog prog.c -lgdbm

      If you wish to use the dbm or ndbm compatibility routines, you must
      link in the gdbm_compat library as well.  For example:



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 GDBM(3)                            GDBM                             GDBM(3)
 GDBM User Reference                                     GDBM User Reference

                                July 8, 2016



           gcc -o prog proc.c -lgdbm -lgdbm_compat


 BUG REPORTS
      Send bug reports to <bug-gdbm@gnu.org>.

 SEE ALSO
      gdbm_dump(1), gdbm_load(1), gdbmtool(1).

 AUTHORS
      by Philip A. Nelson, Jason Downs and Sergey Poznyakoff.

 COPYRIGHT
      Copyright c 1990 - 2016 Free Software Foundation, Inc.

      GDBM is free software; you can redistribute it and/or modify it under
      the terms of the GNU General Public License as published by the Free
      Software Foundation; either version 1, or (at your option) any later
      version.

      GDBM is distributed in the hope that it will be useful, but WITHOUT
      ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
      FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      for more details.

      You should have received a copy of the GNU General Public License
      along with GDBM.  If not, see <http://gnu.org/licenses/gpl.html>

 CONTACTS
      You may contact the original author by:
         e-mail:  phil@cs.wwu.edu
        us-mail:  Philip A. Nelson
      Computer Science Department
      Western Washington University
      Bellingham, WA 98226

      You may contact the current maintainers by:
         e-mail:  downsj@downsj.com
      and
         e-mail:  gray@gnu.org












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