In modern C++, the filesystem library allows portable interaction with directories and directory-like structures providing functions such as listing directory contents and moving files. After the C++17 standard, the contents of the Filesystems Technical Specification are now part of modern C++ and are implemented in the filesystem library.
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What Is the filesystems library in C++ 17?
The Filesystem Library is defined in the <filesystem> header (as a std::filesystem namespace), it provides operations on file systems and their components, such as paths, regular files, and directories. This library allows portable interaction with directories and directory-like structures by using classes and non-member functions. It is modernized well for C++, it is largely modeled on POSIX, and flexible enough to be implementable for different operating systems. After the C++17 standard, the contents of the Filesystems Technical Specification are now part of modern C++ and are implemented in the filesystem library.
The filesystem library was previously being used by the boost.filesystem which was published in 2015. In C++17, they merged this library into modern C++. Note that, the boost implementation libraries are still available on more compilers and platforms for many benefits.
The filesystem library consists of a lot of file operations (copy, move, permissions), directory operations (listing, iterating, …), and path operations.
Some of classes are path, directory_entry, directory_iterator, perms, file_status, … and some of non-member functions in this library are copy, copy_file, current_path, exists, file_size, rename, remove, status, is_directory, is_empty, …
Are there some examples of how to use the filesystems library in C++?
Here are some examples that can be used with C++17 and standards beyond it,
How can I use std::filesystem::current_path in C++ 17?
In C++17, we can use std::filesystem::current_path to get current path on runtime. Here is a simple filesystem example in modern C++ that you can get current path.
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#include <iostream> #include <filesystem> int main() { std::cout << "Current path is " << std::filesystem::current_path() << std::endl; system("pause"); return 0; } |
In my C++ Builder 12 console application example, it gives the current folder of my project that has executable file,
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Current path is C:\Users\yilmaz\Documents\Embarcadero\Studio\Projects\Win32\Debug |
How can I use std::filesystem::copy and std::filesystem::rename in C++ 17?
In C++17, we can use std::filesystem::copy to copy files and directories, and we can use std::filesystem::rename to rename or move files. Here is an example of how you can copy a file and move it by renaming it.
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#include <iostream> #include <filesystem> int main() { std::filesystem::copy("C:\\test.txt", "D:\\test.txt"); std::filesystem::rename("D:\\test.txt", "D:\\mytest.txt"); system("pause"); return 0; } |
How can I use std::filesystem::directory_iterator in C++ 17?
In C++17, the std::filesystem::directory_iterator is an iterator that iterates over the directory_entry elements of a directory. It doesn’t list sub directories.
Here is an example that lists the contents of a directory (a kind of dir command).
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#include <iostream> #include <filesystem> int main() { std::string mypath = "C://"; for (auto& line : std::filesystem::directory_iterator(mypath) ) { std::cout << line.path() << std::endl; } system("pause"); return 0; } |
Of course, there are many examples of the classes and methods of the filesystem library. If you want to know more about the filesystem library, in C++ Builder 12, Virtual Assist (VA) is very useful. If you type std::filesystem:: into Visual Assist it automatically lists all members of the filesystem namespace. If you type a method i.e. std::filesystem::copy it gives all variations of its parameters as shown below.
For more details about changes in C++17 standard, please see this https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0218r0.html, or other papers here P0219R1, P0317R1, P0392R0, P0430R2, P0492R2, LWG 2956.
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