CS215 - Lec 3 single record operations

� Writing and reading data back from a file.

� Extraction operator VS getline function.

� Write a single record on a file.

� Read a single record from a file.

� Build Company class.

� Overload operators for the Company class.

� Build template for programs.

Dr. Hussien M. Sharaf 2

� What is the problem with reading data from files?

� Since we are reading from files in form of streams of bytes therefore we can not differentiate between tokens.

� Fortunately, the extraction operator in C++ can tokenize streams.

� But some fields could include more than one token.


Hussien M. Sharaf [email protected] CS215

Name EmailID Course


� 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.


� Write the previous data into a text file then try reading using:

1. Method: .get (buf,'\n');

2. Method: .getline (buf,'\n');

3. Function: getline (ifstream, string_Line,'\n');

// Write a text file

#include <iostream>

#include <fstream>

#include <string>

using namespace std;

int main () {

string line,token;

char buf[1000];

ofstream myfilePut("example.txt",ios::trunc);

if (myfilePut.is_open())

{

myfilePut<<"Hussien M. Sharaf\n";

}


myfilePut.close();ifstream myfileGet ("example.txt");if (myfileGet.is_open()){ while (! myfileGet.eof())

{//myfileGet >>token;myfileGet.get (buf,'\n');line=buf;myfileGet.seekg(0,ios::beg);myfileGet.getline (buf,'\n');line=buf;cout << line<< endl;}

//clear flags any bad operation

myfileGet.clear();

myfileGet .seekg(0,ios::beg );

getline (myfileGet,line,'\n');

cout << line<< endl;

//clear flags any bad operation

myfileGet.clear();

myfileGet .seekg(0,ios::beg );

//use exttaction op to read into buf

while (! myfileGet.eof())

{

myfileGet>>buf;

cout << buf<< endl;

}


//clear flags any bad operationmyfileGet.clear();myfileGet .seekg(0,ios::beg );//use exttaction op to read into stringwhile (! myfileGet.eof()){

myfileGet>>line;cout << line<< endl;

}

myfileGet .close();}else cout << "Unable to open file"; system("Pause");return 0;}

� Try reading using:

1. Extraction op.

2. Function: getline (ifstream,string_Line,'\n');

� myfileGet>>line;

� getline (myfileGet,line,'\n');

� Does the extraction op. identify separators other then space?


� It was noticed that the extraction operator “>>” reads until first token separator [space, “,”, “;”, TAB, “\r” ]

� What are your suggestions for reading a collection of fields?

#include <iostream>

#include <fstream>

#include <string>

using namespace std;

string ExtendstringLength(string In, intrequiredSize, string appendchar)

{

while (In.length()<requiredSize )

In=In.append(appendchar);

return In;

}

int main () {

string line,token;

int ID;

string FullName,Course,Email;

char buf[1000];

ID=811;


Course="CS215";FullName ="Hussien M. Sharaf";Email="[email protected]";Course.append("@");FullName=ExtendstringLength(FullName,20,"@");Email = ExtendstringLength(Email,50,"@");ofstream myfilePut("example.txt",ios::trunc);if (myfilePut.is_open()){myfilePut<<ID<<Course<<FullName<<Email ;}myfilePut.close();

ifstream myfileGet ("example.txt");if (myfileGet.is_open()){

myfileGet>>ID;cout << ID<< endl;myfileGet>>Course ;cout << Course << endl;//clear flags any bad

operationmyfileGet.clear();myfileGet .seekg(0,ios::beg

);myfileGet>>ID;cout << ID<< endl;

myfileGet.get( buf,7) ;Course=buf;


Course=Course.substr(0,5);cout << Course << endl;

myfileGet.get( buf,21) ;FullName=buf;FullName=FullName.erase(FullName.find("@"));cout << FullName<< endl;

myfileGet.get( buf,51) ;Email=buf;Email=Email.erase(Email.find("@"));cout << Email<< endl;

}system("Pause");return 0;

}


� What are the required fields? And what are their types?

1. CompanyName

2. ContactName

3. TitleofBusiness

4. Address

5. City

6. ZipCode

7. Phone

8. Fax

9. Email

10. WebSite

11. CompanyCode

12. CompanyDescription

� Each field is qualified by double quotes “.

A screen shot of a file sample

#include <iostream>using namespace std;class Company{

string CompanyCode, CompanyDescription ,CompanyName, ContactName, TitleofBusiness, Address,City, ZipCode, Phone, Fax, Email, WebSite;

};

1. Write default constructor, copy constructor.2. Overload “=” operator and “==” [optional]3. Overload “<<” and “>>” for ostream and istream. 4. Write a driver that uses the above class to read a single line that

contain all fields of a company. Each field is quoted by double quotes “field_Value” and separated from the next field by a comma ,

Example:"155","All",“A-z Maintenance",“Malek",“-","902 Bestel Avenue - Garden Grove“,..



User Interface

Classes containing any processing of data

//Declarations

while (ExitProgram!=true)

{ //take user choice

switch (UserChoice)

{ case 'I':

case 'i':

//handle user Choice

case'E':

case'e':ExitProgram=true; break;

}

}

system("pause");


1. Start by determining Output.

2. List the inputs.

3. Think about processing.

Check Ex 3:� Continue building a class for CompanyInfo:

1. Write default constructor, copy constructor.2. Overload “=” operator and “==” [optional]3. Overload “<<” and “>>” for ostream and istream and use

the delimiter method for reading and writing each field. Each field is required to be enclosed inside two double quotes i.e “…..”

� Write a driver to use this class based on the template Menu.


� 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.


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

2. Compress the solution folder using winrar.

3. Rename the compressed file as follows:

StudentName_ID_A3.rar

4. Email to: [email protected] your ID in the subject.

5. With subject: “FO – Assignment#3 -ID”


Date post:	24-Dec-2014
Category:	Technology
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CS215 - Lec 3 single record operations

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