CS215 - Lec 2 file organization

� Introduction to file organization:◦ What? Why? How?

� File organization challenge

� History of File organization

� Streams operations

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� File organization : is rearranging data structures and its operations in order to enhance performance of data reading and writing from and to secondary storage media (disks).

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Data structures

RAM/Main memory

Operations for accessing data

File structures File processing

Secondary memory

(Disks)

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�File structures: is organization of data representation on secondary devices such as disks.

�File processing (Streams Operations): The processing (treatment) of data on secondary devices such as disks. It involves transferring data between secondary devices and RAM.

�This will be built based on your knowledge of

Data Structures.

� The study of file organization and processing is needed in order to retrieve data from secondary storage into RAM so that programs can process them.

� The retrieval process must be as fast as possible.

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1. Minimize number of trips to the disk in order to get desired information.

2. Grouping related information so that we are likely to get everything we need with only one trip to the disk (e.g. name, address,

phone number, account balance).

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� Reading/writing data is slow (since electronic and mechanical)

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� ofstream: Stream class to write on files

� ifstream: Stream class to read from files

� fstream: Stream class to both read and write from/to files.

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ios::in Open for input operations.

ios::out Open for output operations.

ios::binary Open in binary mode.

ios::ateSet the initial position at the end of the file.If this flag is not set to any value, the initial position is the beginning of the file.

ios::app

All output operations are performed at the end of the file, appending the content to the current content of the file. This flag can only be used in streams open for output-only operations.

ios::truncIf the file opened for output operations already existed before, its previous content is deleted and replaced by the new one.

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ofstream myfile;

myfile.open ("example.bin", ios::out | ios::app | ios::binary);

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class default mode parameter

ofstream ios::out

ifstream ios::in

fstream ios::in | ios::out

ofstream myfile ("example.bin", ios::out | ios::app | ios::binary);

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if (myfile.is_open())

myfile << "This is a line.\n";

myfile.close();

Check that the stream is

opened.

Write data into stream.

Close the stream and

hence the modifications are

saved into the file.

� tellg() and tellp()

These two member functions return an integer representing the current position of the get stream pointer (in the case of tellg) or the put stream pointer (in the case of tellp).

� seekg(count, offset) and seekp(offset, direction)

These functions allow programmers to change the position of the get and put stream pointers.

ios::beg offset counted from the beginning of the stream

ios::cur offset counted from the current position of the stream pointer

ios::end offset counted from the end of the stream

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What does this program do?- Obtain the size of a file

� Check Examples 2.1 and 2.2

� Write a program that generates a random array of 12 integers and then write each element into a new line in a file “ArrayElem.txt”.

� Send the source code project (after zipping it) to my email:

n.abdelhameed@fci-cu.edu.eg

Follow instructions made in the last page. Make sure to send your ID. Students who don’t send their IDs clearly will loose marks.

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� Check Examples 2.1 and 2.2 using VS2008 or VS2010

� Write a program that reads a given number of lines from “ArrayElem.txt” and displays them into one line separated by comma “,”.

� Send the source code project (after zipping it) to my email:

n.abdelhameed@fci-cu.edu.eg

� Follow instructions made in the last page. Make sure to send your ID. Students who don’t send their IDs clearly will loose marks.

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� Next week is the deadline.

� No excuses.

� Don’t wait until last day.

� I can help you to the highest limit within the next 3 days.

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1. Delete the “bin” and “obj” folders.

2. Compress the solution folder using winrar.

3. Rename the compressed file as follows:

StudentName_ID_A1.rar

StudentName_ID_A2.rar

4. Email to: n.abdelhameed@fci-cu.edu.eg

with your ID in the subject.

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