How to implement a file search

//size of record = 100 b
//size of blonck = 4 kb
struct record{
    char name [26] ;
    char family[30] ;
    char stu_no [20] ;
    char mobil [20] ;
    record * pnext ;
};

record search ( record pdata ) 
{
	char item [30];
	char x ;
	fstream file ;
	file.open ( "file2.dat" ) ;
	int med ;
	int low = 0 ;
//counterb is number of blonck
	int hight = counterb - 1 ;
	while ( low <=hight )
	{
		med = ( low + hight )/2 ;
		file.seekp (4096*med , ios::beg ) ;
		for ( int i = 0 ; i < 30 ; i++ )
		{
			file.read ( &x , 1 ) ;
			item[i] = x ;
		}
		for ( int i = 0 ; i < 30 ; i++ )
		{
			int y = strcmp ( item , pdata.family  ) ;
			if ( y == 0 )
			{
				file >> pdata.family >> pdata .name >> pdata .mobil >> pdata .stu_no ;	 
				return pdata ;
			}
			if ( y < 0 )
			{
				file.seekp (-4096 , ios::beg ) ;
				for ( int i = 0 ; i < 30 ; i++ )
				{
					file.read ( &x , 1 ) ;
					item[i] = x ;
				}
				y = strcmp ( item , pdata.family  ) ;
				med = (low + med -1)/2 ;
			}
			if ( y > 0 )
			{
				file.seekp (counterr*100 , ios::beg ) ;
				for ( int i = 0 ; i < 30 ; i++ )
				{
					file.read ( &x , 1 ) ;
					item[i] = x ;
				}
				y = strcmp ( item , pdata.family  ) ;
				med = (hight + med +1)/2 ;
			}
		}
	}
}