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} Continue different methods for record organization.
} Continue with the company class; } Use length indicator, } Use index. } Buffering records into memory.
Dr. Hussien M. Sharaf 2
Dr. Hussien M. Sharaf 3
Fixed length of
bytes Variable length
Length indicator Record
delimiter Record index
} To store the record length just ahead of the record.
Dr. Hussien M. Sharaf 4
4. Length indicator
Record 3 Record 4 Record 1 Record 2
} Problems: 1. The field length must not be too long (less than
256 bytes) to be stored in a single byte. 2. Needs more programming effort. 3. Requires at least two disk trips for each record.
210 250 180 190
} Store the byte offset of each record into a list stored in another file.
Dr. Hussien M. Sharaf 5
5. Index
} Problems: 1. Two files are used: one for the data and another for
Student_ID offset
20090172 1023 Record1
\n
\n
20090222 211 Record2 \n
20090343 62 Record3 \n
2009393 143 Record4 \n
Ø The purpose is to read entire record into RAM then use string operations to split it into fields.
Ø Instead of accessing the disk many times to read each field, only one disk trip is needed for each record.
Ø String manipulations done in RAM is much faster than doing same number of disk trips.
Dr. Hussien M. Sharaf 6
Ø It is another form of string variables. Ø A stream is built upon a string variable to give
the same functionalities and behavior of file streams.
Ø Since we have done a lot of coding on the basis of streams then we can make use of our code.
Ø The final target is to do fields splitting in RAM instead of doing it on disk.
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} When overloading operators << and >> it is better to use ostream and istream which are the parents of ofstream and ifstream
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ostream istream
iostream
fstream
ofstream cout
ifstream cin
ostringstring istringstream
stringstream
http://www.cplusplus.com/reference/iostream/
Ø Continue using the CompanyInfo class: Read the whole record into a stringstream. Then pass the stringStream to a method that extracts each field into its correct data-member inside the CompanyInfo class.
Dr. Hussien M. Sharaf 10
