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Posted 6 Apr 2003

Memory mapped files and flat table primitives.

, 6 Apr 2003
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Source C++ classes for persisting flat table data.


Let's say you need to store and read an array of some structures to or from the hard drive in your application.

For instance: you may have a structure like this:

struct record {
  char first_name[32];
  char last_name[64];
  record() { first_name[0] = 0; last_name[0] = 0; }
  void set(const char* first, const char *last)
    strncpy(first_name, first, sizeof(first_name)-1);
    strncpy(last_name, last, sizeof(last_name)-1);

And you would like to persist an array of them.

Instead of using expensive (in many senses) classical database solution, you may write the following:

#include "tl_mm_file.h"

int main(int argc, char* argv[])
  tool::table<record> tbl;

/* writing/creating table of "record"s */"c:/test.tbl",true);



/* reading it */"c:/test.tbl");
  for(unsigned int i = 0; i <; i++)
    printf("%s %s\n",
      tbl(i).last_name );

 return 0;

You just need to include mm_file.h and mm_file.cpp in your project and you are done.


  1. Easy and fast. This method of accessing persistent data has nearly zero time overload for opening/closing datasets and eliminates need of intermediate buffers a.k.a. "current record".
  2. It provides direct access to the records in the table in a random manner.
  3. Compact and self-sufficient implementation.


  1. Only fixed size structures are supported.
  2. Access by key (hash-table, b-tree, etc.) should be implemented separately (if needed).


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About the Author

Founder Terra Informatica Software
Canada Canada
Andrew Fedoniouk.

MS in Physics and Applied Mathematics.
Designing software applications and systems since 1991.

W3C HTML5 Working Group, Invited Expert.

Terra Informatica Software, Inc.

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Comments and Discussions

GeneralVery Good Stuff Pin
AbhishekBK28-Apr-06 0:08
memberAbhishekBK28-Apr-06 0:08 
QuestionCan you add multi-table support? Pin
任远科9-Jan-04 20:13
member任远科9-Jan-04 20:13 
AnswerRe: Can you add multi-table support? Pin
c-smile9-Jan-04 21:22
memberc-smile9-Jan-04 21:22 
GeneralRe: Can you add multi-table support? Pin
任远科10-Jan-04 6:10
member任远科10-Jan-04 6:10 
GeneralGood approach but... Pin
Dimitris Vassiliades9-Apr-03 11:51
memberDimitris Vassiliades9-Apr-03 11:51 
GeneralRe: Good approach but... Pin
c-smile9-Apr-03 12:34
memberc-smile9-Apr-03 12:34 
GeneralRe: Good approach but... Pin
raminx14-Apr-03 21:54
memberraminx14-Apr-03 21:54 
GeneralRe: Good approach but... Pin
c-smile15-Apr-03 8:12
memberc-smile15-Apr-03 8:12 
raminx wrote:
what features have you used that CMemFile wouldn't provide?

OK, here goes sacred knowledge about mm files:

MFC::CMemFile creates file ALIKE temporary memory buffer. After "closing" it all information is gone. It just frees memory.

mm_file (memory mapped file) on the contrary, it physically creates file and maps a section of the file to memory (RAM). It use plain memory pointers to access file data "directly". After closing such file you will have your data stored on the disk automatically (persisted). And you can reopen it and access your data in the next app. session in the same manner.

Therefore you'll have persistent table data with random access like an array in memory.
With near zero time for opening/closing/access operations and amount of code.

Pretty much as DBF file engine implementation. But in 80 lines of code.

raminx wrote:
why did you use different operators for reading & writing

It is possible to change "()" on to " const& [] const".
But for explicit call of "read-only []" you need to declare your table variable as
const table<my_record> myTableReadOnly;
Without const modifier C++ will always use "writing []".

My personal preference is to use separate operator () just to be sure that I am calling right function.


Andrew Fedoniouk.
Terra Informatica Consulting.
GeneralRecommendations Pin
peterchen7-Apr-03 1:21
memberpeterchen7-Apr-03 1:21 
GeneralThanks Pin
jhaga7-Apr-03 0:30
memberjhaga7-Apr-03 0:30 

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