std::filesystem::filesystem_error

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

#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 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 [/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

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