Streaming I/OHandling the input and output of

your program

2

What you knowO To read in from a console: cinO To output to a console: cout

O Example:O cout << “Enter a number: “;O cin >> number;

3

How this happensO Data streams are like queues (more

in 241)O Reading from data streams

O console adds to the back of streamO cin reads from the front of stream

O Writing to data streamsO cout adds to the back of the streamO console reads from the front of the

stream

4

Reading From StreamsStream

1 2 3 4

cin

5

Writing to streamsStream

1 2 3 4

cout

6

What makes this possible

O iostream (the power of inheritance)O istream – reads file from streamO ostream – writes file to stream

O Limitation:O Only works with console I/O

7

Using files for I/OO #include <fstream>

O fstream header defines three types to support file I/OO ifstream – reads from a fileO ofstrem – writes to a fileO fstream – read and write to same file

8

Accessing the filesO Create the stream

O ifstream infile; //unbound input file stream

O ofstream outfile; //unbound output file stream

O Bind to a fileO infile.open(“listOfSponsors.txt”);O outfile.open(“listOfAds.txt”);

9

First things first…O The absolute first thing to do is check to

make sure the file opens.O Flags get set when something goes wrong

O badbit – indicates system level failureO failbit – reading wrong type of dataO eofbit – set when eof is reached

O How to check?O if(strm.good()){O //its ok to read from the file

}

10

Learning to readO General syntax: streamName >> variableO Reads until whitespace

O Example: Reading One ValueO infile >> myChar;

O Example: Reading until end of fileO while(infile.good()){

O infile >> sponserName;O sponserVector.push_back(sponserName);

O }

11

Learning to writeO General syntax: streamName <<

variable;

O Examples:O outfile << myInt << endl;O outfile << someString << endl;O outfile << firstRadioAd << endl;

12

Last but not leastO Always remember to close your

streamO General syntax: strm.close();

O Example:O infile.close();O outfile.close();

O Allows for the stream to be bound again

13

Put it all togetherO #include fstream //allows file i/oO using namespace std;O void main(){

O ifstream read; //create an instreamO ofstream write; //create an outstreamO read.open(“someFile.txt”); //bind to fileO write.open(“resultFile.txt”); //bind to fileO while(read.good() && write.good()){

O read >> variable;O write << variable << endl;

O }O read.close();O write.close();

O }

14

Questions?