File input using ifstream in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is ifstream used for in C++?

<p><code>ifstream</code> is a class in C++ used to read data from files. It stands for input file stream.</p>

beginner

How do you open a file named data.txt for reading using ifstream?

You create an ifstream object and pass the filename to its constructor or use the open() method:

std::ifstream file("data.txt");
// or
std::ifstream file;
file.open("data.txt");

beginner

How can you check if a file was opened successfully with ifstream?

Use the is_open() method or check the stream in a boolean context:

if (file.is_open()) {
  // file opened
}
// or
if (file) {
  // file opened
}

beginner

How do you read a line of text from a file using ifstream?

Use std::getline() with the ifstream object and a string variable:

std::string line;
std::getline(file, line);

beginner

Why should you close an ifstream after reading a file?

Closing the file releases system resources and ensures all data is properly handled. Use file.close() when done reading.

Which header file must you include to use ifstream in C++?

A <iostream>

B <fstream.h>

C <fstream>

D <file>

The <fstream> header provides file stream classes including ifstream.

What does ifstream file("input.txt"); do?

A Creates a file named input.txt

B Opens input.txt for reading

C Writes data to input.txt

D Deletes input.txt

This line opens the file input.txt for reading using ifstream.

How do you check if the file was opened successfully?

A if (file.is_open())

B if (file.open())

C if (file.closed())

D if (file.read())

The is_open() method returns true if the file is open.

Which function reads a whole line from a file into a string?

A std::getline(file, stringVar)

B file.getline()

C file.readLine()

D file.read()

std::getline() reads a line from the file stream into a string.

What happens if you forget to close an ifstream?

A The program crashes immediately

B The file is saved twice

C The file is deleted automatically

D The file remains open and resources may be wasted

Not closing a file can waste system resources until the program ends.

Explain step-by-step how to read text from a file using ifstream in C++.

Think about opening, reading, checking, and closing the file.

What are the benefits of using ifstream for file input in C++?

Consider why streams are helpful for file handling.