std::errc

#include <filesystem>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <string>
#include <system_error>
#include <thread>
 
void print_error(const std::string & details, std::error_code error_code)
{
 std::string value_name;
 if (error_code == std::errc::invalid_argument)
 value_name = "std::errc::invalid_argument";
 if (error_code == std::errc::no_such_file_or_directory)
 value_name = "std::errc::no_such_file_or_directory";
 if (error_code == std::errc::is_a_directory)
 value_name = "std::errc::is_a_directory";
 if (error_code == std::errc::permission_denied)
 value_name = "std::errc::permission_denied";
 
 std::cout << details << ":\n "
 << std::quoted (error_code.message())
 << " (" << value_name << ")\n\n";
}
 
void print_errno(const std::string & details, int errno_value = errno)
{
 print_error(details, std::make_error_code (std::errc(errno_value)));
}
 
int main()
{
 std::cout << "Detaching a not-a-thread...\n";
 try
 {
 std::thread ().detach();
 }
 catch (const std::system_error & e)
 {
 print_error("Error detaching empty thread", e.code());
 }
 
 std::cout << "Opening nonexistent file...\n";
 std::ifstream nofile{"nonexistent-file"};
 if (!nofile.is_open())
 print_errno("Error opening nonexistent file for reading");
 
 std::cout << "Reading from directory as a file...\n";
 std::filesystem::create_directory ("dir");
 std::ifstream dir_stream{"dir"};
 [[maybe_unused]] char c = dir_stream.get();
 if (!dir_stream.good())
 print_errno("Error reading data from directory");
 
 std::cout << "Open read-only file for writing...\n";
 std::fstream {"readonly-file", std::ios::out};
 std::filesystem::permissions ("readonly-file", std::filesystem::perms::owner_read );
 std::fstream write_readonly("readonly-file", std::ios::out);
 if (!write_readonly.is_open())
 print_errno("Error opening read-only file for writing");
}

Detaching a not-a-thread...
Error detaching empty thread:
 "Invalid argument" (std::errc::invalid_argument)
 
Opening nonexistent file...
Error opening nonexistent file for reading:
 "No such file or directory" (std::errc::no_such_file_or_directory)
 
Reading from directory as a file...
Error reading data from directory:
 "Is a directory" (std::errc::is_a_directory)
 
Open read-only file for writing...
Error opening read-only file for writing:
 "Permission denied" (std::errc::permission_denied)