Question

In this program, I am reading “key.pc.db” file and printing its mid value.

#include <fstream>
#include <conio.h>
#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#include <sys/stat.h>
using namespace std;
int main( int argc, char *argv[] )
{
        ifstream  fp;     
        int mval;
        int sizek;
        struct stat filek;
        int min, max, mid;
        if(stat("key.pc.db", &filek) ==0 )
             sizek=filek.st_size;
        sizek=sizek/sizeof(int);
        min=0;
        max=sizek-1;
        mid=(min+max)/2;    
        printf("mid %d ",mid);
        fp.open( "key.pc.db", ios::in | ios::binary ); 
        fp.seekg(mid, ios::beg);
        fp.read( (char *) &mval, (int) sizeof( int ) );
        printf("%d mval ", mval);
        getch();
        return 1;
}

In this program also I am reading the same file but I am storing the value of the file in an array and then printing the mid value. The mid index for both the program shows the same but the value comes out to be different. Why so?

#include <fstream>
#include <conio.h>
#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#include <sys/stat.h>
using namespace std;
int main( int argc, char *argv[] )
{
        ifstream  fp;     
        int index;
        int sizek;
        int kval;
        struct stat filek;
        int min, max, mid;
        int i=0;
        if(stat("key.pc.db", &filek) ==0 )
             sizek=filek.st_size;
        sizek=sizek/sizeof(int);
        int k[sizek];
        fp.open( "key.pc.db", ios::in | ios::binary );  
        fp.read( (char *) &kval, (int) sizeof( int ) );
        while( !fp.eof() ) 
         {
               k[i++]=kval;
               fp.read( (char *) &kval, (int) sizeof( int ) );
         }
        min=0;
        max=sizek-1;
        mid=(min+max)/2;
        printf(" index %d ", mid);
        printf(" kmid %d ", k[mid]);
        getch();
        return 1;
}

Answer 1

You’re seeking to the wrong point in the file in the first case. You should be seeking to mid*sizeof(int) rather than mid.