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External Sorting

Posted By: Joe Evans     Category: C Programming     Views: 4830

Program of External Sorting.

Code for External Sorting in C Programming

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>

void shownums ( char * ) ;
void split ( char * ) ;
void sort ( char * ) ;

void main( )
{
    char str[67] ;

    clrscr( ) ;

    printf ( "Enter file name: " ) ;
    scanf ( "%s", str ) ;

    printf ( "Numbers before sorting:\n" ) ;
    shownums ( str ) ;

    split ( str ) ;
    sort ( str ) ;

    printf ( "\nNumbers after sorting:\n" ) ;
    shownums ( str ) ;

    getch( ) ;
}

/* Displays the contents of file */
void shownums ( char *p ) { FILE *fp ; int i ; fp = fopen ( p, "rb" ) ; if ( fp == NULL ) { printf ( "Unable to open file." ) ; getch( ) ; exit ( 0 ) ; } while ( fread ( &i, sizeof ( int ), 1, fp ) != 0 ) printf ( "%d \t", i ) ; fclose ( fp ) ; } /* Splits the original file into two files */
void split ( char *p ) { FILE *fs, *ft ; longint l, count ; int i ; fs = fopen ( p, "rb" ) ; if ( fs == NULL ) { printf ( "Unable to open file." ) ; getch( ) ; exit ( 0 ) ; } ft = fopen ( "temp1.dat", "wb" ) ; if ( ft == NULL ) { fclose ( fs ) ; printf ( "Unable to open file." ) ; getch( ) ; exit ( 1 ) ; } fseek ( fs, 0L, SEEK_END ) ; l = ftell ( fs ) ; fseek ( fs, 0L, SEEK_SET ) ; l = l / ( sizeof ( int ) * 2 ) ; for ( count = 1 ; count <= l ; count++ ) { fread ( &i, sizeof ( int ), 1, fs ) ; fwrite ( &i, sizeof ( int ), 1, ft ) ; } fclose ( ft ) ; ft = fopen ( "temp2.dat", "wb" ) ; if ( ft == NULL ) { fclose ( fs ) ; printf ( "Unable to open file." ) ; getch( ) ; exit ( 2 ) ; } while ( fread ( &i, sizeof ( int ), 1, fs ) != 0 ) fwrite ( &i, sizeof ( int ), 1, ft ) ; fcloseall ( ) ; } /* Sorts the file */
void sort ( char *p ) { FILE *fp[4] ; char *fnames[ ] = { "temp1.dat", "temp2.dat", "final1.dat", "final2.dat" } ; int i, j = 1, i1, i2, flag1, flag2, p1, p2 ; longint l ; while ( 1 ) { for ( i = 0 ; i <= 1 ; i++ ) { fp[i] = fopen ( fnames[i], "rb+" ) ; if ( fp[i] == NULL ) { fcloseall( ) ; printf ( "Unable to open file." ) ; getch( ) ; exit ( i ) ; } fseek ( fp[i], 0L, SEEK_END ) ; l = ftell ( fp[i] ) ; if ( l == 0 ) gotoout ; fseek ( fp[i], 0L, SEEK_SET ) ; } for ( i = 2 ; i <= 3 ; i++ ) { fp[i] = fopen ( fnames[i], "wb" ) ; if ( fp[i] == NULL ) { fcloseall( ) ; printf ( "Unable to open file." ) ; getch( ) ; exit ( i ) ; } } i = 2 ; i1 = i2 = 0 ; flag1 = flag2 = 1 ; while ( 1 ) { if ( flag1 ) { if ( fread ( &p1, sizeof ( int ), 1, fp[0] ) == 0 ) { /* If first file ends then the whole content of second
file is written in the respective target file */
while ( fread ( &p2, sizeof ( int ), 1, fp[1] ) != 0 ) fwrite ( &p2, sizeof ( int ), 1, fp[i] ) ; break ; } } if ( flag2 ) { if ( fread ( &p2, sizeof ( int ), 1, fp[1] ) == 0 ) { /* If second file ends then the whole content of first
file is written in the respective target file */
fwrite ( &p1, sizeof ( int ), 1, fp[i] ) ; while ( fread ( &p1, sizeof ( int ), 1, fp[0] ) != 0 ) fwrite ( &p1, sizeof ( int ), 1, fp[i] ) ; break ; } } if ( p1 < p2 ) { flag2 = 0 ; flag1 = 1 ; fwrite ( &p1, sizeof ( int ), 1, fp[i] ) ; i1++ ; } else { flag1 = 0 ; flag2 = 1 ; fwrite ( &p2, sizeof ( int ), 1, fp[i] ) ; i2++ ; } if ( i1 == j ) { flag1 = flag2 = 1 ; fwrite ( &p2, sizeof ( int ), 1, fp[i] ) ; for ( i2++ ; i2 < j ; i2++ ) { if ( fread ( &p2, sizeof ( int ), 1, fp[1] ) != 0 ) fwrite ( &p2, sizeof ( int ), 1, fp[i] ) ; } i1 = i2 = 0 ; i == 2 ? ( i = 3 ) : ( i = 2 ) ; } if ( i2 == j ) { flag1 = flag2 = 1 ; fwrite ( &p1, sizeof ( int ), 1, fp[i] ) ; for ( i1++ ; i1 < j ; i1++ ) { if ( fread ( &p1, sizeof ( int ), 1, fp[0] ) != 0 ) fwrite ( &p1, sizeof ( int ), 1, fp[i] ) ; } i1 = i2 = 0 ; i == 2 ? ( i = 3 ) : ( i = 2 ) ; } } fcloseall( ) ; remove ( fnames[0] ) ; remove ( fnames[1] ) ; rename ( fnames[2], fnames[0] ) ; rename ( fnames[3], fnames[1] ) ; j *= 2 ; } out : fcloseall( ) ; remove ( p ) ; rename ( fnames[0], p ) ; remove ( fnames[1] ) ; }
  
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Joe Evans
Joe Evans author of External Sorting is from London, United Kingdom.
 
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