NAME¶

std::filesystem::copy_file - std::filesystem::copy_file

Synopsis¶

Defined in header <filesystem>
bool copy_file( const std::filesystem::path& from, (1) (since C++17)
const std::filesystem::path& to );
bool copy_file( const std::filesystem::path& from,

const std::filesystem::path& to, (2) (since C++17)

std::error_code& ec );
bool copy_file( const std::filesystem::path& from,

const std::filesystem::path& to, (3) (since C++17)

std::filesystem::copy_options options );
bool copy_file( const std::filesystem::path& from,

const std::filesystem::path& to, (4) (since C++17)
std::filesystem::copy_options options,

std::error_code& ec );

1,2) The default, equivalent to (3,4) with copy_options::none used as options.
3,4) Copies a single file from from to to, using the copy options indicated by
options. The behavior is undefined if there is more than one option in any of the
copy_options option group present in options (even in the groups not relevant to
filesystem::copy_file).
* If !filesystem::is_regular_file(from) (either because the source file doesn't
exist or because it is not a regular file), report an error.
* Otherwise, if the destination file does not exist,

* copies the contents and the attributes of the file to which from resolves to the
file to which to resolves (symlinks are followed).
* Otherwise, if the destination file already exists,

* report an error if any of the following is true:

* to and from are the same as determined by filesystem::equivalent(from, to);
* to is not a regular file as determined by !filesystem::is_regular_file(to);
* none of the filesystem::copy_file control options are set in options.
* Otherwise, if copy_options::skip_existing is set in options, do nothing.
* Otherwise, if copy_options::overwrite_existing is set in options, copy the
contents and the attributes of the file to which from resolves to the file to
which to resolves.
* Otherwise, if copy_options::update_existing is set in options, only copy the
file if from is newer than to, as defined by filesystem::last_write_time().

The non-throwing overloads return false if an error occurs.

Parameters¶

from - path to the source file
to - path to the target file
ec - out-parameter for error reporting in the non-throwing overload

Return value¶

true if the file was copied, false otherwise.

Exceptions¶

Any overload not marked noexcept may throw std::bad_alloc if memory allocation
fails.

1,3) Throws std::filesystem::filesystem_error on underlying OS API errors,
constructed with from as the first path argument, to as the second path argument,
and the OS error code as the error code argument.
2,4) Sets a std::error_code& parameter to the OS API error code if an OS API call
fails, and executes ec.clear() if no errors occur.

Notes¶

The functions involve at most one direct or indirect call to filesystem::status(to)
(used both to determine if the file exists, and, for
filesystem::copy_options::update_existing option, its last write time).

Error is reported when filesystem::copy_file is used to copy a directory: use
filesystem::copy for that.

filesystem::copy_file follows symlinks: use filesystem::copy_symlink or
filesystem::copy with filesystem::copy_options::copy_symlinks for that.

Example¶

// Run this code

#include <filesystem>
#include <fstream>
#include <iostream>
namespace fs = std::filesystem;

int main()
{
fs::create_directory("sandbox");
std::ofstream("sandbox/file1.txt").put('a');

fs::copy_file("sandbox/file1.txt", "sandbox/file2.txt");

// now there are two files in sandbox:
std::cout << "file1.txt holds: "
<< std::ifstream("sandbox/file1.txt").rdbuf() << '\n';
std::cout << "file2.txt holds: "
<< std::ifstream("sandbox/file2.txt").rdbuf() << '\n';

// fail to copy directory
fs::create_directory("sandbox/abc");
try
{
fs::copy_file("sandbox/abc", "sandbox/def");
}
catch (fs::filesystem_error& e)
{
std::cout << "Could not copy sandbox/abc: " << e.what() << '\n';
}
fs::remove_all("sandbox");
}

Possible output:¶

file1.txt holds: a
file2.txt holds: a
Could not copy sandbox/abc: copy_file: Is a directory: "sandbox/abc", "sandbox/def"

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3014 C++17 error_code overload marked noexcept but can noexcept removed
allocate memory

See also¶

copy_options specifies semantics of copy operations
(C++17) (enum)
copy_symlink copies a symbolic link
(C++17) (function)
copy copies files or directories
(C++17) (function)