Memory mapped files and flat table primitives.

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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).