File System Library in C++17

In this article, we will learn about the File System library in C++17 and with examples. <filesystem> header was added in C++17 and introduces a set of classes, functions, and types that simplify file system operations. In simple words, we can say that the filesystem library provides tools that help us to simplify working with files and directories.

In earlier versions, performing file and directory operations was often a bulky and mistake-susceptible task as it required the use of platform-specific functions and libraries. The file system library was added to cope with these troubles, offering a portable and standardized way to paint with the file system.

Syntax

To use the features of the file system library, we have to import <filesystem> header using #include preprocessor.

#include <filesystem>

All the identifiers of <filesystem> headers are defined inside the std::filesystem namespace.

Classes in <filesystem> Header

The following are some commonly used classes of file system libraries.

S. No.	Class	Description
1	filesystem::path	The path class represents the path of the directory or the file.
2	filesystem::copy_options	This class represents the available copy options.
3	filesystem::directory_options	Represents the options for iterating through directory contents.
4	filesystem::filesystem_error	This class defines the exceptions that are thrown by the filesystem functions in case of errors.
5	filesystem::file_status	This class stores information about the type of the file and available permissions.
6	filesystem::file_time_type	It represents file time values
7	filesystem::perms	This function stores the information about the file access permission.
8	filesystem::perm_options	It specifies the semantics of permissions operations.
9	filesystem::space_info	This struct stores the data about the storage in the specified path.
10	filesystem::file_type:	It is used to represent different types of a file or directory.

Examples of File System library

Example 1: Creating a Directory and File

In this example, we will create a new file in a newly created directory. The parent directory looks like this before execution:

Parent Directory Before Execution

C++

// C++ Program to illustrate the use of filesystem classes
// and features
#include <filesystem>
#include <fstream>
#include <iostream>

// for simplicity
using namespace std;
using namespace std::filesystem;

int main()
{
    // Define the path to create directory
    path directorypath = "mydirectory";

    // To check if the directory exist or not, create it if
    // doesn't exist
    if (!exists(directorypath)) {
        create_directory(directorypath);
        cout << "Directory created: " << directorypath
             << endl;
    }

    // Define the file path within the directory and
    // combining the directory
    path filepath = directorypath / "my_file.txt";

    // Create and open the file for writing using
    // std::ofstream
    ofstream file(filepath);
    if (file.is_open()) {
        // Write data to the file
        file << "Hello, FileSystem!";
        file.close();
        cout << "File created: " << filepath << endl;
    }
    else {
        // Handle the case if any error occured
        cerr << "Failed to create file: " << filepath
             << endl;
    }

    return 0;
}

Output

Directory created: "mydirectory"
File created: "mydirectory/my_file.txt"

Explanation

In this example, a directory is created named “mydirectory”. It checks if the directory exists and creates it if no longer. Sooner or later, a file named “my_file.Txt” is defined within this directory. The code then opens this file for writing using std::ofstream. If a success, it writes the text “Hello, FileSystem!” to the file and closes it. If any errors occur in the directory of the listing or file advent procedure, suitable error messages are displayed.

Parent Directory After Execution

New Directory

Contents of New File

Example 2: Listing Files in a Directory

C++

// C++ program to list all the files and folder in the given
// directory
#include <filesystem>
#include <iostream>

using namespace std;
using namespace std::filesystem;

int main()
{
    // Define the directory path to list files from
    path directorypath = "";

    // To check if the directory exists or not
    if (exists(directorypath)
        && is_directory(directorypath)) {
        // Loop through each item (file or subdirectory) in
        // the directory
        for (const auto& entry :
             directory_iterator(directorypath)) {
            // Output the path of the file or subdirectory
            cout << "File: " << entry.path() << endl;
        }
    }
    else {
        // Handle the case where the directory doesn't exist
        cerr << "Directory not found." << endl;
    }

    return 0;
}

Output

File: "mydirectory/my_file.txt"
File: "mydirectory/my_file2.txt"
File: "mydirectory/my_file3.txt"
File: "mydirectory/my_file4.txt"

Explanation

In this example, first, we define the directorypath to indicate the target directory. Then we wrote the condition to check if the directory exists or not using fs::exists() and fs::is_directory(). If it exists, it iterates through its contents using a range-based for loop with fs::directory_iterator(), and prints each item’s path to the standard output.

Example 3: Renaming a File

C++

// C++ program to rename a file
#include <filesystem>
#include <iostream>

using namespace std;
using namespace std::filesystem;

int main()
{
    // Define the path of old file and new file
    path oldFilePath = "mydirectory/my_file.txt";
    path newFilePath = "mydirectory/renamed_file.txt";

    // Check if the old file exists
    if (exists(oldFilePath)) {
        // Rename the file
        rename(oldFilePath, newFilePath);
        cout << "File renamed to: " << newFilePath << endl;
    }
    else {
        // Handle the case where the old file doesn't exist
        cerr << "File not found: " << oldFilePath << endl;
    }

    return 0;
}

Output

File renamed to: "mydirectory/renamed_file.txt"

Explanation

In this example, first, we define the path for the old file and the new file. Then, wrote a condition to check if the old file exists in the directory or not with fs::exists(), and if it is discovered, then rename it using fs::rename(). A success message will be displayed with the new file path. and if the old file isn’t found, it prints an error message.

Advantages and Features of <filesystem>

Let’s explore some of the key features provided by the <filesystem> library:

• Path Manipulation: The file system library introduces the std::filesystem::path class to represent file system paths. This class encapsulates the platform-specific path representation and provides an easy way to manipulate and inspect paths.
• File and Directory Operations: The file system library includes functions to perform common file and directory operations such as creating, removing, renaming, and checking for the existence of files and directories.
• Error Handling: The <filesystem> library provides exceptions to handle errors during file system operations. You can catch exceptions like std::filesystem::filesystem_error to gracefully handle failures.
• Portable Code: One of the main advantages of using <filesystem> is the portability it brings to your code. Since it abstracts platform-specific details, you can write code that works consistently across different operating systems.