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/*
C & Data Structures
Published in Feb 2004 by CHARLES RIVER MEDIA
Author: P. S. Deshpande, O. G. Kakde
SKU: 1584503386
ISBN: 1584503386
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX 50
typedef struct {
char name[10];
int key;
} file_record;
/* this function adds the relatiuve addres to the index for a key */
void create_index(long index[], int key, long rel_add ) {
index[key] = rel_add;
}
/* this function writes a record to the file */
void write_rec(FILE *fp, file_record rec) {
fwrite(&rec,sizeof(rec),1,fp);
}
void main() {
long rel_add;
int key;
file_record frec;
long index[MAX];/* an index list*/
int n,i;
FILE *recfile=NULL,*ifile=NULL;
/* this initializes the index list to all ? */
for(i=0; i< MAX; i++)
index[i]= (-1);
recfile=fopen("mfile","w");
if(recfile == NULL) {
printf("Error in openeing file mfile\n");
exit(0);
}
rel_add = 0 ;
do {
printf(" Enter the data vlue and the key of the record to be added to file mfile\n");
scanf("%s %d",frec.name,&frec.key);
while(index[frec.key] != (-1)) {
printf(" A record with this key value already exist in a file enter record key value\n");
scanf("%s %d",frec.name,&frec.key);
}
create_index(index,frec.key,rel_add);
write_rec(recfile,frec);
rel_add = ftell(recfile);
/* this sets the relative address for the next record to be
the value of current file position pointer in bytes from
the beginning of the file */
printf("Enter 1 to continue adding records to the file\n");
scanf("%d",&n);
}while(n == 1);
ifile=fopen("index_file","w");
if(ifile == NULL) {
printf("Error in openeing file index_file\n");
exit(0);
}
fwrite(index,sizeof(index),1,ifile);/*writes the complete index into the index_file */
fclose(recfile);
fclose(ifile);
printf("Enter 1 if you want to retrieve a record\n");
scanf("%d",&n);
if( n == 1) {
ifile=fopen("index_file","r");
if(ifile == NULL) {
printf("Error in openeing file index_file\n");
exit(0);
}
fread(index,sizeof(index),1,ifile);
/* reads the complete index into the index list from the index_file*/
fclose(ifile);
recfile=fopen("mfile","r");
if(recfile == NULL) {
printf("Error in openeing file mfile\n");
exit(0);
}
}
printf("THE CONTENTS OF FILE IS \n");
while( (fread(&frec,sizeof(frec),1,recfile)) != 0)
printf("%s %d\n",frec.name,frec.key);
do {
printf("Enter the key of the record to be retrieved\n");
scanf("%d",&key);
rel_add = index[key]; /*gets the relative address of the record from index list */
if( (fseek(recfile,rel_add,SEEK_SET))!= 0) {
printf("Error\n");
exit(0);
}
fread(&frec,sizeof(frec),1,recfile);
printf("The data value of the retrieved record is %s\n",frec.name);
printf("Enter 1 if you want to retrieve a record\n");
scanf("%d",&n);
} while(n == 1);
fclose(recfile);
}
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