此头文件是文件系统支持库的一部分。本篇介绍filesystem命名空间的一些函数。

 示例代码：

#include <filesystem>
#include <iostream>
#include <string>
#include <cstdlib>
#include <fstream>
#include <cstdint>
#include <system_error>

namespace fs = std::filesystem;

void show(std::filesystem::path x, std::filesystem::path y)
{
	std::cout << "x:\t\t " << x << "\ny:\t\t " << y << '\n'
		<< "relative(x, y):  "
		<< std::filesystem::relative(x, y) << '\n'
		<< "proximate(x, y): "
		<< std::filesystem::proximate(x, y) << "\n\n";
}

void demo_exists(const fs::path& p, fs::file_status s = fs::file_status{})
{
	std::cout << p;
	if (fs::status_known(s) ? fs::exists(s) : fs::exists(p))
		std::cout << " exists\n";
	else
		std::cout << " does not exist\n";
}

struct HumanReadable
{
	std::uintmax_t size{};

private:
	friend std::ostream& operator<<(std::ostream& os, HumanReadable hr)
	{
		int o{};
		double mantissa = hr.size;
		for (; mantissa >= 1024.; mantissa /= 1024., ++o);
		os << std::ceil(mantissa * 10.) / 10. << "BKMGTPE"[o];
		return o ? os << "B (" << hr.size << ')' : os;
	}
};


int main(int, char const* argv[])
{
	//path current_path example  返回或设置当前工作目录 
	std::cout << "当前路径为 " << fs::current_path() << '\n';

	//path temp_directory_path example 返回一个适用于临时文件的目录 
	std::cout << "temp_directory_path " << fs::temp_directory_path() << '\n';
	//absolute example  当前路径/foo.c  组成一个绝对路径 
	std::filesystem::path p = "foo.c";
	std::cout << p << " 的绝对路径为 " << fs::absolute(p) << '\n';
	
	// create_directory/create_directories example 创建新目录 
	auto temp = fs::current_path();
	auto dir1 = temp / "abc";
	auto dir2 = temp / "abb/c2/e";
	std::filesystem::create_directory(dir1); //只能创建单个目录
	std::filesystem::create_directories(dir2);//可以创建多级目录
	std::filesystem::current_path(dir2);//设置当前路径

	// canonical/weakly_canonical  example 组成一个规范路径
	//"D:\\vscpp\\cpp20\\cpp20standard\\filesystem"
	auto p1 = std::filesystem::path("../../c2/./e");
	auto p2 = std::filesystem::path("../no-such-file");
	std::cout << "当前路径为 "
		<< std::filesystem::current_path() << '\n'
		<< p1 << " 的规范路径为 "
		<< std::filesystem::canonical(p1) << '\n'
		<< p2 << " 的弱规范路径为 "
		<< std::filesystem::weakly_canonical(p2) << '\n';

	try
	{
		[[maybe_unused]] auto x_x = std::filesystem::canonical(p2);
		// 不会抵达此处
	}
	catch (const std::exception& ex)
	{
		std::cout << p2 << " 的规范路径抛出了异常：\n"
			<< ex.what() << '\n';
	}
	//relative / proximate 组成一个相对路径 
	show("/a/b/c", "/a/b");
	show("/a/c", "/a/b");
	show("c", "/a/b");
	show("/a/b", "c");

	//auto temp = fs::current_path();
	auto dir3 = temp / "abb\\c2";
	auto dir4 = temp / "abb\\dir4";
	auto file1 = temp / "abb\\file1.txt";
	auto file2 = temp / "abb\\file2.txt";
	std::cout << "dir3======================" << dir3 << "\n";
	std::ofstream(file1).put('a');
	fs::copy(file1, file2); // 复制文件
	fs::copy(dir3, dir4); // 复制目录（非递归）
	const auto copyOptions = fs::copy_options::update_existing
		| fs::copy_options::recursive
		| fs::copy_options::directories_only
		;
	auto dirAbc = temp / "abc";
	auto dir5 = temp / "abb_copy";
	fs::copy(dirAbc, dir5, copyOptions);
	static_cast<void>(std::system("tree"));
	// remove/remove_all 移除一个文件或空目录 / 移除一个文件或递归地移除一个目录及其所有内容
	fs::remove(file1);
	fs::remove(file2);
	fs::remove_all(dirAbc);
	fs::remove_all(dir5);

	//exists example 检查路径是否指代既存的文件系统对象 
	const fs::path sandbox{ temp/"sandbox" };
	fs::create_directory(sandbox);
	std::ofstream{ sandbox / "file" }; // 创建常规文件
	//fs::create_symlink("non-existing", sandbox / "symlink");

	demo_exists(sandbox);

	for (const auto& entry : fs::directory_iterator(sandbox))
		demo_exists(entry, entry.status()); // 使用来自 directory_entry 的缓存状态

	fs::remove_all(sandbox);

	// 硬链接等价  equivalent example 检查两个路径是否指代同一文件系统对象 
	fs::path path1 = ".";
	fs::path path2 = fs::current_path();
	if (fs::equivalent(path1, path2))
		std::cout << path1 << " is equivalent to " << path2 << '\n';

	// 符号链接等价 
	for (const fs::path lib : {"/lib/libc.so.6", "/lib/x86_64-linux-gnu/libc.so.6"})
	{
		try
		{
			path2 = lib.parent_path() / fs::read_symlink(lib);
		}
		catch (std::filesystem::filesystem_error const& ex)
		{
			std::cout << ex.what() << '\n';
			continue;
		}

		if (fs::equivalent(lib, path2))
			std::cout << lib << " is equivalent to " << path2 << '\n';
	}
	//file_size example 返回文件的大小 
	fs::path example = "bug.nc";
	fs::path path3 = fs::current_path() / example;
	std::ofstream(path3).put('a'); // 创建大小为 1 的文件
	std::cout << example << " size = " << fs::file_size(path3) << '\n';
	fs::remove(path3);

	path3 = argv[0];
	std::cout << path3 << " size = " << HumanReadable{ fs::file_size(path3) } << '\n';

	try
	{
		std::cout << "尝试获取目录的大小:\n";
		[[maybe_unused]] auto x_x = fs::file_size("/dev");
	}
	catch (fs::filesystem_error& e)
	{
		std::cout << e.what() << '\n';
	}

	for (std::error_code ec; fs::path bin : {"cat", "mouse"})
	{
		bin = "/bin" / bin;
		if (const std::uintmax_t size = fs::file_size(bin, ec); ec)
			std::cout << bin << " : " << ec.message() << '\n';
		else
			std::cout << bin << " size = " << HumanReadable{ size } << '\n';
	}

	//rename example 移动或重命名一个文件或目录 
	std::filesystem::path path4 = std::filesystem::current_path() / "sandbox";
	std::filesystem::create_directories(path4 / "from");
	std::ofstream{ path4 / "from/file1.txt" }.put('a');
	std::filesystem::create_directory(path4 / "to");

	fs::rename(path4 / "from/file1.txt", path4 / "to/file2.txt"); // OK
//	fs::rename(path4 / "from", path4 / "to/subdir"); // OK

	//space example确定文件系统上的可用空闲空间
	std::error_code ec;
	const std::filesystem::space_info si = std::filesystem::space(path4, ec);
	std::cout << "capacity: " << si.capacity << "\tavailable:" << si.available << "\tfree:" << si.free << '\n';

	//std::filesystem::remove_all(path4);

	std::cout << "hello world\n";
	return 0;
}

运行结果：

参考：

标准库标头 <filesystem> (C++17) - cppreference.com