file_io.md

The C++17 standard introduced the <filesystem> library, which provides a robust way of handling file and directory operations. Note that <filesystem> is largely about manipulating file paths, directories, and file attributes, rather than reading or writing file content.

Basic Types

• Path: Represents a file path, provided by std::filesystem::path.
• Directory Entry: An object of type std::filesystem::directory_entry represents an element in a directory and holds a path object.
• Directory Iterator: Type std::filesystem::directory_iterator is used to iterate over directories.

File Operations

• File Exists: exists()
• Create Directory: create_directory()
• Create Directories: create_directories()
• Remove: remove() Remove All: remove_all() to remove directories and their contents.
• Rename: rename()
• Copy: copy() and copy_file()
• Copy Options: Flags like copy_options::recursive, copy_options::overwrite_existing, etc.
• Resize File: resize_file()
• File Time: Manipulate or access the last write time using last_write_time()

File Attributes

• File Size: file_size()
• File Type: is_regular_file(), is_directory(), etc.
• Permissions: permissions(), perms, perm_options
• File Status: status(), symlink_status()

Filesystem Queries

• Space Info: space()
• Current Path: current_path()
• Absolute Path: absolute()
• Relative Path: relative()

Path Manipulations

• Concatenation: Using / operator
• Decomposition: root_name(), root_directory(), root_path(), relative_path(), parent_path(), filename(), stem(), extension()

Iterating Directories

• Recursive Directory Iterator: std::filesystem::recursive_directory_iterator
• Filtering Iterators: Using directory_options to filter the iteration.

Examples

Checking if a File or Directory Exists

#include <iostream>
#include <filesystem>

int main() {
    std::filesystem::path p("some_file.txt");
    if (std::filesystem::exists(p)) {
        std::cout << p << " exists.\n";
    } else {
        std::cout << p << " does not exist.\n";
    }
    return 0;
}

Creating a Directory

#include <iostream>
#include <filesystem>

int main() {
    std::filesystem::path dir("new_directory");
    if (std::filesystem::create_directory(dir)) {
        std::cout << "Directory created successfully.\n";
    } else {
        std::cout << "Failed to create directory.\n";
    }
    return 0;
}

Listing All Files in a Directory

#include <iostream>
#include <filesystem>

int main() {
    std::filesystem::path dir(".");
    for (const auto &entry : std::filesystem::directory_iterator(dir)) {
        std::cout << entry.path() << std::endl;
    }
    return 0;
}

Deleting a File

#include <iostream>
#include <filesystem>

int main() {
    std::filesystem::path file_to_remove("some_file.txt");
    if (std::filesystem::remove(file_to_remove)) {
        std::cout << "File removed successfully.\n";
    } else {
        std::cout << "Failed to remove file.\n";
    }
    return 0;
}

File Size and File Type

#include <iostream>
#include <filesystem>

int main() {
    std::filesystem::path p("some_file.txt");
    if (std::filesystem::exists(p)) {
        auto fsize = std::filesystem::file_size(p);
        std::cout << "File size: " << fsize << " bytes.\n";
        if (std::filesystem::is_regular_file(p)) {
            std::cout << p << " is a regular file.\n";
        }
    }
    return 0;
}