How to Use std::filesystem in C++: Syntax and Examples

To use std::filesystem in C++, include the header <filesystem> and use the namespace std::filesystem. It provides functions to work with files and directories like checking existence, creating directories, and iterating files.

Syntax

Include the <filesystem> header and use the std::filesystem namespace. Common classes and functions include:

• std::filesystem::path: represents file or directory paths.
• exists(path): checks if a file or directory exists.
• create_directory(path): creates a new directory.
• remove(path): deletes a file or directory.
• directory_iterator(path): iterates over directory contents.

cpp

#include <filesystem>
#include <iostream>

namespace fs = std::filesystem;

int main() {
    fs::path p = "example.txt";  // path object
    if (fs::exists(p)) {
        std::cout << p << " exists.\n";
    } else {
        std::cout << p << " does not exist.\n";
    }
    return 0;
}

Example

This example shows how to create a directory, check if it exists, list files inside it, and remove the directory.

cpp

#include <filesystem>
#include <iostream>

namespace fs = std::filesystem;

int main() {
    fs::path dir = "test_dir";

    // Create directory if it doesn't exist
    if (!fs::exists(dir)) {
        fs::create_directory(dir);
        std::cout << "Directory created: " << dir << "\n";
    } else {
        std::cout << "Directory already exists: " << dir << "\n";
    }

    // List contents (should be empty)
    std::cout << "Contents of " << dir << ":\n";
    for (const auto& entry : fs::directory_iterator(dir)) {
        std::cout << "  " << entry.path().filename() << "\n";
    }

    // Remove directory
    fs::remove(dir);
    std::cout << "Directory removed: " << dir << "\n";

    return 0;
}

Output

Directory created: test_dir
Contents of test_dir:
Directory removed: test_dir

Common Pitfalls

Common mistakes when using std::filesystem include:

• Not checking if a path exists before accessing it, causing exceptions.
• Confusing relative and absolute paths.
• Trying to remove non-empty directories with remove() instead of remove_all().
• Forgetting to handle exceptions thrown by filesystem operations.

Always use try-catch blocks or check conditions before operations.

cpp

#include <filesystem>
#include <iostream>

namespace fs = std::filesystem;

int main() {
    fs::path dir = "nonexistent_dir";

    // Wrong: assuming directory exists
    // This will throw if directory doesn't exist
    // for (const auto& entry : fs::directory_iterator(dir)) {
    //     std::cout << entry.path() << "\n";
    // }

    // Right: check existence first
    if (fs::exists(dir)) {
        for (const auto& entry : fs::directory_iterator(dir)) {
            std::cout << entry.path() << "\n";
        }
    } else {
        std::cout << dir << " does not exist.\n";
    }

    return 0;
}

Output

nonexistent_dir does not exist.

Quick Reference

Function	Description
fs::exists(path)	Check if a file or directory exists
fs::create_directory(path)	Create a new directory
fs::remove(path)	Remove a file or empty directory
fs::remove_all(path)	Remove a directory and all contents
fs::directory_iterator(path)	Iterate over directory contents
fs::path	Class to represent file or directory paths

Key Takeaways

Include and use namespace std::filesystem to access filesystem features.

Always check if paths exist before performing operations to avoid exceptions.

Use fs::create_directory to make directories and fs::remove or fs::remove_all to delete files or directories.

Use directory_iterator to loop through files in a directory.

Handle exceptions or errors when working with filesystem operations.