std::filesystem::filesystem_error

 

C++

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Filesystem library (C++17)

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Technical specifications

Symbols index

External libraries

 

Filesystem library

Classes
filesystem::path filesystem::filesystem_error filesystem::directory_entry filesystem::directory_iterator filesystem::recursive_directory_iterator      filesystem::file_status	filesystem::space_info filesystem::file_type filesystem::perms filesystem::perm_options filesystem::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::canonicalfilesystem::weakly_canonical filesystem::relativefilesystem::proximate filesystem::copy filesystem::copy_file filesystem::copy_symlink filesystem::create_directory filesystem::create_directories filesystem::create_hard_link filesystem::create_symlink filesystem::create_directory_symlink filesystem::current_path	filesystem::exists filesystem::equivalent filesystem::file_size filesystem::hard_link_count filesystem::last_write_time filesystem::permissions filesystem::read_symlink filesystem::remove filesystem::remove_all filesystem::rename filesystem::resize_file filesystem::space filesystem::status filesystem::symlink_status filesystem::temp_directory_path
File types
filesystem::is_block_file filesystem::is_character_file filesystem::is_directory filesystem::is_empty filesystem::status_known	filesystem::is_fifo filesystem::is_other filesystem::is_regular_file filesystem::is_socket filesystem::is_symlink

 

filesystem_error

Member functions

filesystem_error::filesystem_error

filesystem_error::operator=

filesystem_error::path1filesystem_error::path2

filesystem_error::what

Inherited from std::system_error

system_error::code

 

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.

Inheritance diagram

Member functions

(constructor)	constructs the exception object (public member function)
operator=	replaces the exception object (public member function)
path1path2	returns the paths that were involved in the operation that caused the 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 [virtual]	returns an explanatory string (virtual public member function of std::system_error)

Inherited from std::runtime_error

Inherited from std::exception

Member functions

(destructor) [virtual]	destroys the exception object (virtual public member function of std::exception)
what [virtual]	returns an explanatory string (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() respectively 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 <system_error>
#include <filesystem>
#include <iostream>
 
int main()
{
    const std::filesystem::path from{"/nonexistent1/a"}, to{"/nonexistent2/b"};
    try {
        std::filesystem::copy_file(from, to); // throws: files do not exist
    }
    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 [/nonexistent1/a] [/nonexistent2/b]
path1(): "/nonexistent1/a"
path2(): "/nonexistent2/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