1. Lecture 16
File I/O
Richard Gesick

2. File Input / Output
Consider that a program may want to make its data persistent (or not rely upon the user for input)
Reading from and writing to a file is conceptually the same as reading/writing to the console

3. Streams Streams hold data
Input streams provide data to the program (keyboard and ReadLine)
The program places data onto output streams (console and WriteLine)

4. Process: Open the file stream
(many "modes" - read, write, append, create, etc.)
Do what you need to do (read/write)
Close the file stream
(freeing it for use by other programs)
You can imagine that there is an "active cursor" that is moved around the file as you read/write

5. Opening / Closing Files
Opening the file
StreamReader sr = new StreamReader("data.txt");
StreamWriter sw = new StreamWriter("output.txt");
Closing the file
sr.Close();
sw.Close();

6. Reading data Reading data from the file
int x = Int32.Parse(sr.ReadLine()); or
string data = sr.ReadLine();
while (data != null) {
string[] info = data.Split(' ');
. . .
data= sr.ReadLIne(); }

7. loading data from a file with varied formatting:
private void LoadWorld() {
StreamReader sr = new StreamReader("world.txt");
world_width = Int32.Parse(sr.ReadLine());
world_height = Int32.Parse(sr.ReadLine());
show_width = Int32.Parse(sr.ReadLine());
show_height = Int32.Parse(sr.ReadLine());
world_background= new int[world_width, world_height];
//more on next slide

8. loading a "game world" information:
// continued from previous…
string row;
char[] delims = { ',' };
string[] tokens;
for (int r = 0; r < world_height; r++) {
row = sr.ReadLine();
tokens = row.Split(delims);
for (int c = 0; c < world_width; c++) {
world_background[c, r] = Int32.Parse(tokens[c]); } }
sr.Close(); }

9. Writing to files
StreamWriter, if the file doesn’t exist, it will create that file and opens the file for output.
Many options.
default: opens the file, deletes existing data
StreamWriter sw = new StreamWriter("outfile.txt");
Opens the file, appends data to existing data
StreamWriter sw = new StreamWriter("outfile.txt",true);

10. Writing data Writing data to the file Or
sw.WriteLine(42); Or
sw.WriteLine(lname + " " + fname + " " + avg);
Or if the object has a to string that will provide the necessary information:
foreach ( Person p in personList)
sw.WriteLine(p);