Notes

Outline

COM1100 Fundamentals of Computer Science –Winter 2000 Lecture 21 03/02/00

Lecture today File stream as function arguments Examples of reading and writing text file Declare file stream variable Open a file by indicating its name Get data from a file Write data into a file Close a file

File stream as function arguments A file stream object can be a function argument. The only requirement is that the function’s formal parameter be a reference to the appropriate stream, either as : ifstream& or ofstream&

Example 1 – ifstream& Write a function GetInputFile that will receive one input file stream as argument, and will open the file stream by asking the user to enter a file name.

Example 2 – ofstream& Write a function GetOutputFile that will receive one output file stream as argument, and will open the file stream by asking the user to enter a file name.

Question 1 Suppose there is a data file PaintData.txt with the following contents: circle 100 100 20 rectangle 40 40 90 80 rectangle 140 140 190 180 circle 200 200 50 The first column in each line is a label. If the label is equal to “circle”, then the following data in this line are xcenter, ycenter and radius for painting a circle. If the label is equal to “rectangle”, then the following data in this line are x1, y1, x2 and y2 for painting a rectangle. Read all the data from the file and paint either circls or rectangle according to the corresponding labels.

Question 1  -- Solution ifstream myFile; // declare an input file stream GetInputFile(myFile); // call function GetInputFile (see slide 4)   int x1, y1, x2, y2; // declare variables for rectangle int xcenter, ycenter, r; // declare variables for circle string label; // declare variable for label   while (myFile.peek() != EOF) { // test if at the End Of File (EOF) myFile >> label; // read label if (label == "circle") { myFile >> xcenter >> ycenter >> r; // read xcenter, ycenter and r PaintCircle(xcenter,ycenter,r); // paint a circle } else if (label =="rectangle") { myFile >> x1 >> y1 >> x2 >> y2; // read x1, y1, x2, y2 PaintRect(x1,y1,x2,y2); // paint a rectangle } }  myFile.close(); // close the file stream

Question 2 and solution

Question 3 and solution

Question 4

Question 4 -- solution