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std::filesy...system_error(3)  C++ Standard Libary std::filesy...system_error(3)

NAME
     std::filesystem::filesystem_error - std::filesystem::filesystem_error

Synopsis
	Defined in header <filesystem>
	class filesystem_error; 	(since C++17)

	The  class std::filesystem::filesystem_error defines an exception object
     that is
	thrown on failure by the throwing overloads  of  the  functions  in  the
     filesystem
	library.

	std-filesystem-filesystem error-inheritance.svg

					Inheritance diagram

Member functions
	constructor   constructs the exception object
		      (public member function)
	operator=     replaces the exception object
		      (public member function)
	path1	      returns the paths that were involved in the operation that
     caused the
	path2	      error
		      (public member function)
	what	      returns the explanatory string
		      (public member function)

     Inherited from std::system_error

Member functions
	code	  returns error code
		  (public member function of std::system_error)
	what	  returns an explanatory string
	[virtual] (virtual public member function of std::system_error)

     Inherited from std::runtime_error

     Inherited from std::exception

Member functions
	destructor   destroys the exception object
	[virtual]    (virtual public member function of std::exception)
	what	     returns an explanatory string
	[virtual]    (virtual public member function of std::exception)

Notes
	In order to ensure that copy functions of filesystem_error are noexcept,
     typical
	implementations  store	an object holding the return value of what() and
     two
	std::filesystem::path objects referenced by path1() and path2()  respec-
     tively in a
	separately-allocated reference-counted storage.

	Currently the MS STL implementation is non-conforming: objects mentioned
     above are
	stored directly in the filesystem object, which makes the copy functions
     not
	noexcept.

Example
     // Run this code

      #include <filesystem>
      #include <iostream>
      #include <system_error>

      int main()
      {
	  const std::filesystem::path from{"/none1/a"}, to{"/none2/b"};

	  try
	  {
	      std::filesystem::copy_file(from,	to); // throws: files do not ex-
     ist
	  }
	  catch (std::filesystem::filesystem_error const& ex)
	  {
	      std::cout << "what():  " << ex.what() << '\n'
			<< "path1(): " << ex.path1() << '\n'
			<< "path2(): " << ex.path2() << '\n'
			<< "code().value():    " << ex.code().value() << '\n'
			<< "code().message():  " << ex.code().message() << '\n'
			<< "code().category(): " <<  ex.code().category().name()
     << '\n';
	  }

	  // All functions have non-throwing equivalents
	  std::error_code ec;
	  std::filesystem::copy_file(from, to, ec); // does not throw
	  std::cout  <<  "\nNon-throwing form sets error_code: " << ec.message()
     << '\n';
      }

Possible output:
      what():  filesystem error: cannot copy file: No  such  file  or  directory
     [/none1/a] [/none2/b]
      path1(): "/none1/a"
      path2(): "/none2/b"
      code().value():	 2
      code().message():  No such file or directory
      code().category(): generic

      Non-throwing form sets error_code: No such file or directory

http://cppreference.com 	   2024.06.10	   std::filesy...system_error(3)
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