CS162: Introduction to Computer Science II Streams II 1 - - PDF document

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CS162: Introduction to Computer Science II

Streams II

Inheritance and Streams

We say class B is derived from class A if:

• Class B is a more specific type of Class

A

• Both classes have some things in

common

• Class B has more features

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Inheritance and Streams

Examples from the real-world:

• Cat has a derived from relationship with

Animal

• Car has a derived from relationship with

Vehicle

• Electrical Engineering has a derived

from relationship with Engineering

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Inheritance and Streams

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More specific More general Cat Animal Car Vehicle Electrical Engineering Engineering

Derived From Derived From Derived From

Child Parent

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Inheritance and Streams

C++ example #1

ifstream istream

Derived From

• ifstream is for files
• istream is for input streams (eg. cin is an
• bject of type istream)
• Shared behavior: can use >> on both
• Behavior specific to ifstream: can use open()

and close() on ifstream but not on istream

Child Parent

Inheritance and Streams

C++ example #1

ifstream istream

Derived From

• We say ifstream is derived from istream
• An ifstream object has all the properties of an

istream object

• An ifstream object is also an object of type

istream

Child Parent

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Inheritance and Streams

C++ example #2

• fstream
• stream

Derived From

• ofstream is for files
• ostream is for output streams (eg. cout and

cerr are objects of type ostream)

• Shared behavior: can use << on both
• Behavior specific to ofstream: can use open()

and close()on ofstream but not on ostream

Child Parent

Inheritance and Streams

C++ example #2

• fstream
• stream

Derived From

• We say ofstream is derived from ostream
• An ofstream object has all the properties of an
• stream object
• An ofstream object is also an object of type
• stream

Child Parent

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Inheritance and Streams

void foo1(ifstream& sourceFile) { int n1, n2; sourceFile >> n1 >> n2; cout << n1 << “ + “ << n2 << “ = “ << (n1 + n2) << endl; }

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ifstream fin; fin.open(“input.txt”); foo1(fin); /* Works */ foo1(cin); /* Doesn’t work because cin is not an ifstream */

Inheritance and Streams

void foo2(istream& sourceFile) { int n1, n2; sourceFile >> n1 >> n2; cout << n1 << “ + “ << n2 << “ = “ << (n1 + n2) << endl; }

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ifstream fin; fin.open(“input.txt”); foo2(fin); /* Works */ foo2(cin); /* Works */

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The stringstream class

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stringstream

• This is a handy class for creating strings
• stringstream derived from

iostream which is derived from istream

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stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { std::stringstream ss; ss.clear(); ss.str("1. "); float c = 9.99; ss << "Macho burrito: $" << c; std::cout << ss.str() << std::endl; return 0; }

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stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { std::stringstream ss; ss.clear(); ss.str("1. "); float c = 9.99; ss << "Macho burrito: $" << c; std::cout << ss.str() << std::endl; return 0; }

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Must include this header to use stringstream

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stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { std::stringstream ss; ss.clear(); ss.str("1. "); float c = 9.99; ss << "Macho burrito: $" << c; std::cout << ss.str() << std::endl; return 0; }

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Clears error statuses

stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { std::stringstream ss; ss.clear(); ss.str("1. "); float c = 9.99; ss << "Macho burrito: $" << c; std::cout << ss.str() << std::endl; return 0; }

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Sets the string in stringstream

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stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { std::stringstream ss; ss.clear(); ss.str("1. "); float c = 9.99; ss << "Macho burrito: $" << c; std::cout << ss.str() << std::endl; return 0; }

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Returns the value

• f the stringstream

as a string

stringstream

The code in the previous slides prints out:

• 1. Macho burrito: $9.99

You can also use stringstreams to parse strings (see next slide)

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stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { int s1, s2, s3; std::stringstream ss("100 80 50"); ss >> s1; ss >> s2; ss >> s3; std::cout << (s1+s2+s3)/3.0 << std::endl; return 0; }

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stringstream

#include <sstream> #include <string> #include <iostream> int main(int argc, char** argv) { int s1, s2, s3; std::stringstream ss("100 80 50"); ss >> s1; ss >> s2; ss >> s3; std::cout << (s1+s2+s3)/3.0 << std::endl; return 0; }

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This reads: 100 into s1, 80 into s2, 50 into s3

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stringstream

The code in the previous slide prints out: 76.6667

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