Read/write structures to/from a file

/* +++Date last modified: 05-Jul-1997 */
/*******************************************************************
 * Generic structure <> disk file manipulations. These functions
 * form a basic template for reading and writing structures to a 
 * sequential file. This template is probably most useful for files
 * with 500 or less records and eliminates the need for a more 
 * elaborate file handler such as C-Tree, DB-Vista, Mix etc.
 * Routines to put data in the struct is out of scope here.
 * Written by Lynn Nash 8/28/91 and donated to the public domain.
 */
#include <io.h>
#include <string.h>
#include <stdlib.h>
#include "sniptype.h"
#include "strucfil.h"
 
/*-------------------- general globals ---------------------*/
static long cur_rec = 0;   /* the current record number */
static FILE *fsptr = NULL;  /* fixed record data file pointer */
 
/* if file exists open in read/write mode else create file */
FILE * open_file(char *filename)
{
   if (access(filename, 0) == 0)
      fsptr = fopen(filename, "rb+"); 
   else fsptr = fopen(filename, "wb+"); 
   return fsptr;            /* return the file pointer */
} 
 
/* add new records to the data file */
int datadd(void)
{
   if (fsptr)
   {
      if (fseek(fsptr, 0L, SEEK_END) != 0)
         return Error_; /* seek failure */
      rec.delete_flag = 0; /* active record tag */
      rec.recordnum = (int) (ftell(fsptr) / 
         (long) sizeof(struct blackbook));
      if (fwrite(&rec, sizeof(struct blackbook), 1, fsptr) != 1)
      {
         return Error_; /* write error */
      }
      else
      {
         /* put your clean up code here */ 
         return Success_;
      }
   }
   return Error_;
}
/* tag the last record read in the file as deleted */
int data_delete(void)
{
   if (fsptr)
   {
      if (fseek(fsptr, (long) sizeof(struct blackbook) * -1L,
         SEEK_CUR) != 0)
      {
         return Error_;
      }
      rec.delete_flag = -1;  /* tag the record as deleted */
      if (fwrite(&rec, sizeof(struct blackbook), 1, fsptr) != 1)
         return Error_;
      else return Success_;
   }
   return Error_;
}
/* read a random structure. If successful the global cur_rec will 
 * contain the number of the last record read & it can be compared
 * to the number in the struct as a double check (belt & suspenders)
 */
int data_read(long recnum)
{
   if (fseek(fsptr, (long) sizeof(struct blackbook) * recnum,
      SEEK_SET) != 0)
   {
      return Error_;
   }
   cur_rec = recnum; /* keep tabs on record pointer in global */ 
   /* now read the record into save struct*/
   if (fread(&oldrec, sizeof(struct blackbook), 1, fsptr) != 1)
   {
      return Error_;
   }
   else             /* copy save struct to edit struct */
   {
      memcpy(&rec, &oldrec, sizeof(struct blackbook));
      return Success_;
   }
}
 
/* rewrite the last read record back to disk */
int data_update(void)
{
   if (memcmp(&rec, &oldrec, sizeof(struct blackbook)) == 0)
      return True_; /* no update needed */
   /* back up one record before writing */
   if (fseek(fsptr, (long) sizeof(struct blackbook) * -1L, 
      SEEK_CUR) != 0)
   {
      return Error_; /* seek error */ 
   }
   /* now write the record */
   if (fwrite(&rec, sizeof(struct blackbook), 1, fsptr) != 1)
      return Error_; /* write error */
   return Success_;
}
/* get the next valid record in the file */
int read_forward(void)
{
   do
   {
      cur_rec++; /* upcount the record number */
      if (data_read(cur_rec) != 0)
      {
         cur_rec--; /* decrement the record number */
         return Error_;
      }
   } while (oldrec.delete_flag != 0); /* record read was deleted */
   return Success_;
}
/* get the previous valid record in the file */
int read_backward(void)
{
   do
   {
      cur_rec--; /* decrement the record number */
      if (cur_rec >= 0)
      {
         if ( data_read(cur_rec) != 0 )
         {
            cur_rec++; /* increment the record number */
            return Error_;
         }
      } 
   } while (oldrec.delete_flag != 0); /* record read was deleted */
   return Success_;
}
Upload