File I/O - Quiz

Which header must you include to use std::ifstream and std::ofstream?

What is the safest way to open a file for reading text?

Which open mode will append to an existing text file without truncating it?

Which is the most memory‑efficient way to process a huge log file?

Which statement correctly opens a binary file for both reading and writing?

Which function retrieves the current read position in an ifstream?

What is a practical use of std::istringstream?

Why is std::getline often preferred over operator>> for reading config lines?

Which approach best preserves class invariants when saving an object to a text file?

When writing portable binary files containing integers, what is MOST important?

Which is a good pattern to ensure a file handle is always closed?

Open a text file for reading using std::ifstream and check success.

Write a POD struct to a binary file using std::ofstream::write.

Construct a string stream for parsing a log line.

What is the output of this code reading line by line?

1#include <iostream>
2#include <fstream>
3#include <string>
4int main() {
5    std::istringstream file("one\ntwo\nthree\n");
6    std::string s;
7    int count = 0;
8    while (std::getline(file, s)) {
9        if (!s.empty()) ++count;
10    }
11    std::cout << count << "\n";
12    return 0;
13}

What does the program print about the file size and position?

1#include <iostream>
2#include <fstream>
3int main() {
4    std::istringstream in("abcd");
5    in.seekg(0, std::ios::end);
6    auto size = in.tellg();
7    in.seekg(1, std::ios::beg);
8    auto pos = in.tellg();
9    std::cout << size << " " << pos << "\n";
10    return 0;
11}

What is printed after writing and rereading from a stringstream?

1#include <iostream>
2#include <sstream>
3int main() {
4    std::stringstream ss;
5    ss << 10 << " " << 20;
6    int a = 0, b = 0;
7    ss >> a;
8    ss >> b;
9    std::cout << a + b << "\n";
10    return 0;
11}

What will this binary write/read example output?

1#include <iostream>
2#include <sstream>
3#include <vector>
4int main() {
5    std::stringstream buf(std::ios::in | std::ios::out | std::ios::binary);
6    std::vector<int> v{1,2,3};
7    buf.write(reinterpret_cast<char*>(v.data()), v.size() * sizeof(int));
8    buf.seekg(0);
9    int x[3] = {0,0,0};
10    buf.read(reinterpret_cast<char*>(x), 3 * sizeof(int));
11    std::cout << x[0] << x[1] << x[2] << "\n";
12    return 0;
13}

What is the output when parsing with std::istringstream?

1#include <iostream>
2#include <sstream>
3#include <string>
4int main() {
5    std::string data = "42 cpp 3.5";
6    std::istringstream iss(data);
7    int i; std::string s; double d;
8    iss >> i >> s >> d;
9    std::cout << i << ":" << s << ":" << d << "\n";
10    return 0;
11}

Find the bug in this file reading code

Click on the line(s) that contain the bug.

#include <fstream>

#include <string>

void load(const std::string& path) {

    std::ifstream in(path);

    std::string line;

    while (!in.eof()) {

        std::getline(in, line);

        // process line

    }

}

Find the bug in this binary serialization code

Click on the line(s) that contain the bug.

#include <fstream>

struct Record {

    int id;

    double value;

};

void save(const Record& r) {

    std::ofstream out("rec.dat", std::ios::binary);

    out.write(reinterpret_cast<const char*>(&r), sizeof(&r));

}

Click the line that risks losing buffered data when writing to a file

Click on the line to select.

#include <fstream>

#include <string>

void writeLog(const std::string& msg) {

    std::ofstream log("log.txt");

    log << msg;

    if (!log) return; // check error

}

Click the line that moves the file pointer to the end of the file

Click on the line to select.

#include <fstream>

void inspect() {

    std::ifstream in("data.txt", std::ios::binary);

    in.seekg(0, std::ios::end);

    auto size = in.tellg();

}

Complete the loop that reads a text file line by line and prints it.

Fill in code to write binary data and then seek back to the beginning.

Complete this parsing code using std::istringstream.

Complete the code that positions within a file to read its last character.

Match each stream type with its primary use in file/string I/O.

Click an item on the left, then click its match on the right. Click a matched item to unmatch.

Match each flag with what it controls when opening file streams.

Click an item on the left, then click its match on the right. Click a matched item to unmatch.

Order the typical steps to safely read configuration from a text file.

Drag and drop to reorder, or use the arrows.

Order the steps for writing a POD object to and then reading it from a binary file.

Drag and drop to reorder, or use the arrows.