Lecture 5

Lecture 5, Thu 07/12

File I/O, Midterm 1 Review

File I/O

The standard library contains functionality that help us deal with file I/O.
The library includes:
- ifstream (input file stream)
- ofstream (output file stream)
In order to either read or write to a file, you must open it first. Note that
- opening a file with ifstream on an invalid file does not crash your program.
  - you will have to check if opening the file was successful.
- opening a file with ofstream will overwrite an existing file by default.
  - If the file does not exist, then it creates one.

Working Directory

The directory where you executed your program.
Absolute Path: The entire path to a specific location.
Relative Path: Path that starts at the current directly to a specific location.

Example

// Writing to a file
#include<fstream>

using namespace std;

int main() {
	ofstream out;
	out.open(“outputExample.txt”);
	out << “Writing to file is like writing to the console”) << endl;
	out.close(); // important to close your files.
	return 0;
}

Note the close() function. Without it, our program still works.
- However, closing file streams is important in order to free up resources.

Appending to a File

When we write to a file, it overwrites it.
We can add a parameter to the open method to simply append data to the file.

out.open("outputExample.txt", ios::app);

Example of reading data from a file into the program

input.txt

Line 1
Line 2
Line 3

#include <iostream>
#include <fstream>

using namespace std;

int main() {
	// Reading from a file one line at a time.
	ifstream in;
	in.open("input.txt");
	string line = "";

	if (in.fail()) { // checks if reading the file failed…
		
		// Note: cerr is like cout, but used to display error messages.
		cerr << "Opening file failed" << endl;

		return 0;
	}


	while (!in.eof()) { // checks if we reached the end of file or not
		getline(in, line); // returns the entire line
		cout << line << endl;
	}
	in.close();
	return 0;
}

Midterm 1 Review

Logistics

- Bring studentID and a writing utensil
	- Preferably ink or dark led
	- PLEASE WRITE LEGIBLY!
- No electronic devices
- No book
- No notes

Format
- Will be a mix of questions which may include …
	- short answers
		- Explain, describe, define, …
	- Write some code
	- Fill in the blank
	- True / False, if False explain why
	- Given some code, write the output (basically, be the computer)
- Should take ~ one hour to complete.
	- Will cover a broad range of topics, but probably not everything.

Topics
	- Will cover everything up to Tuesday’s lecture (7/10)
		- File IO will be covered on midterm 2
	- H01 - H03 and all the assigned readings, lecture notes, labs.
	- Knowing simple g++ compilation, vim commands can be on it.

<iostream>
	- cin, cout

C++ Variables and Types
	- int, double, char, string, bool
	- Initializing, assigning, and modifying variables

Boolean and Logical Expressions
	- Boolean and relational operators
	
Control Structures
	- if-else statements
	- multi-way if statements
	- switch statements
	- embedded if statements
	- Loops
		- do-while, while, for
		- continue and break statements
		- Embedded Loops

Functions
	- Declaration, definition, calling
	- Basic memory stack structure