Chapter 3 Interactivity and Expressions

CSC 125 Introduction to C++ programming

Introduction to File Input and Output

Introduction to File Input and Output

Can use files instead of keyboard, monitor screen for program input, output

Allows data to be retained between program runs

Steps:Open the fileUse the file (read from, write to, or both)Close the file

Files: What is Needed

Use fstream header file for file accessFile stream types:

ifstream for input from a fileofstream for output to a filefstream for input from or output to a file

Define file stream objects:ifstream infile;ofstream outfile;

Opening Files

Create a link between file name (outside the program) and file stream object (inside the program)

Use the open member function:infile.open("inventory.dat");outfile.open("report.txt");

Filename may include drive, path info. Output file will be created if necessary;

existing file will be erased first Input file must exist for open to work

Writing Data into a file

Insertion operator (<<) with coutCan use output file stream object and <<

to send data to a file:

outfile << “Happy Birthday!";

Reading data from a file

Stream extraction operator >>Can use input file object and >> to copy

data from file to variables:infile >> studentName;

infile >> studentSSN

>> studentGPA;

Closing Files

Use the close member function:infile.close();outfile.close();

Don’t wait for operating system to close files at program end:may be limit on number of open filesmay be buffered output data waiting to send

to file

Example

Read jokes line by line from the text file jokes.txt and display them on the screen.

Hand Tracing a Program

Hand trace a program: act as if you are the computer, executing a program:step through and ‘execute’ each statement,

one-by-one record the contents of variables after

statement execution, using a hand trace chart (table)

Useful to locate logic or mathematical errors