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Memory mapped files and flat table primitives.

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

Introduction

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 */
  tbl.open("c:/test.tbl",true);

  tbl[0].set("Andrew","Fedoniouk");
  tbl[1].set("Allan","Doe");
  tbl[2].set("Monica","Lester");

  tbl.close();

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

  tbl.close();
 return 0;
}

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

Pros

  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.

Cons

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

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

c-smile
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.
http://terrainformatica.com

Comments and Discussions

 
GeneralVery Good Stuff PinmemberAbhishekBK28-Apr-06 0:08 
Great way of storing data on the disk.
Very simpel to understand, and elegant to impliment.
 
Abhishek
QuestionCan you add multi-table support? Pinmember任远科9-Jan-04 20:13 
AnswerRe: Can you add multi-table support? Pinmemberc-smile9-Jan-04 21:22 
GeneralRe: Can you add multi-table support? Pinmember任远科10-Jan-04 6:10 
GeneralGood approach but... PinmemberDimitris Vassiliades9-Apr-03 11:51 
GeneralRe: Good approach but... Pinmemberc-smile9-Apr-03 12:34 
GeneralRe: Good approach but... Pinmemberraminx14-Apr-03 21:54 
GeneralRe: Good approach but... Pinmemberc-smile15-Apr-03 8:12 
GeneralRecommendations Pinmemberpeterchen7-Apr-03 1:21 
GeneralThanks Pinmemberjhaga7-Apr-03 0:30 

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