C++ File Handling: Open, Read, and Get File Size with Examples

C++ File Handling: Open, Read, and Get File Size

This tutorial provides examples on how to perform basic file operations in C++, including opening files for writing and reading, checking file existence, and getting the file size.

1. Open a File for Writing (ofstream)

#include <fstream>

int main() {
    std::ofstream out('D:\out.txt');
    // Write to file
    out.close();
    return 0;
}

2. Open a File for Reading (ifstream)

#include <fstream>

int main() {
    std::ifstream in;
    in.open('x.json');
    // Read from file
    in.close();
    return 0;
}

3. Check if a File Exists

#include <fstream>
#include <iostream>

int main() {
    std::ifstream in('x.json');
    if (!in.is_open()) {
        std::cout << 'x.json does not exist' << std::endl;
        return 0;
    }
    // Read from file
    in.close();
    return 0;
}

4. Get the File Size using std::filesystem::file_size

#include <fstream>
#include <iostream>
#include <filesystem>

int main() {
    namespace fs = std::filesystem;
    fs::path filePath('x.json');
    if (!fs::exists(filePath)) {
        std::cout << 'x.json does not exist' << std::endl;
        return 0;
    }
    std::uintmax_t fileSize = fs::file_size(filePath);
    std::ofstream out('D:\out.txt');
    out << std::fixed;
    out << std::setprecision(1) << std::setw(5) << std::setfill('*') << fileSize / 1e9 << ' GB' << std::endl;
    out << std::setprecision(2) << std::setw(6) << std::setfill('*') << fileSize / 1e9 << ' GB' << std::endl;
    out << std::setprecision(3) << std::setw(7) << std::setfill('*') << fileSize / 1e9 << ' GB' << std::endl;
    out << std::setprecision(4) << std::setw(8) << std::setfill('*') << fileSize / 1e9 << ' GB' << std::endl;
    out << std::setprecision(5) << std::setw(9) << std::setfill('*') << fileSize / 1e9 << ' GB' << std::endl;
    out.close();
    return 0;
}

These examples demonstrate fundamental C++ file handling techniques. You can build upon these to create more complex file manipulation programs.