CS 173 Lab 5: Output Formatting and File I/O

Objective: In class we discussed using ifstream and ofstream for file input/output. We have also seen if statements and boolean expressions. For this lab you will practice writing C++ programs that incorporate these techniques, and also begin writing robust programs --- programs that can detect and react to problems when they occur.
Additional info: You can use an ifstream or ofstream object as a boolean expression. When you do, it evaluates to true if all previous operations using the object were successful, otherwise it evaluates to false. You can also call the function exit(1) to immediately terminate the execution of your program. This is extremely useful. Observe the following code: 
string ifName = "data.in";
int    i;

// Open the input file
inFile.open(ifName.c_str());

// If the file did not open successfully, we want to display
// a useful message for the user and quit the program.
if (!inFile)
{
    cout << "ERROR: Unable to open " << ifName << endl;
    cout << "Exiting program." << endl;
    exit(1);
}

inFile >> i;
if (!inFile)
{
    cout << "ERROR: Unable to read an integer from " << ifName << endl;
    cout << "Exiting program." << endl;
    exit(1);
}
From this point on, you should use this kind of "if" statement to ensure that your files successfully opened, and that each read of data was successful. If not, then print a helpful error message and terminate your program.

Lab Tasks

This week you will write a C++ program called stocktrack_fileio.cpp. This program is exactly like last week's ( http://webpages.ursinus.edu/rliston/cs173/lab4.html), except input and output will be to/from files (no prompts are necessary) and your programs must be robust. The program will read a series of 10 closing bell values of a particular stock from a file named "stock.in". The program will then print to the a file called "stock.out" a series of lines exactly like last week's program.

Make sure you define the three integer constants that indicate the field widths. These must be based on the length of the string for the column heading using the .length() function. Use those field widths as arguments to each setw().

Finally, this week I would like to see the checklists that you are maintaining of the things *you* need to watch out for in your coding. Check through this list before compiling and add to it as you discover errors.

Notes:
Richard Liston