NAME

std::filesystem::copy - std::filesystem::copy

Synopsis

Defined in header <filesystem>
void copy( const std::filesystem::path& from,

const std::filesystem::path& to );
void copy( const std::filesystem::path& from, (1) (since C++17)
const std::filesystem::path& to,

std::error_code& ec );
void copy( const std::filesystem::path& from,

const std::filesystem::path& to,
std::filesystem::copy_options options );
void copy( const std::filesystem::path& from, (2) (since C++17)
const std::filesystem::path& to,
std::filesystem::copy_options options,

std::error_code& ec );

Copies files and directories, with a variety of options

1) The default, equivalent to (2) with copy_options::none used as options
2) Copies the file or directory from to file or directory 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 copy_file
group).

The behavior is as follows:

* First, before doing anything else, obtains type and permissions of from by no
more than a single call to

* std::filesystem::symlink_status, if copy_options::skip_symlinks,
copy_options::copy_symlinks, or copy_options::create_symlinks is
present in options;
* std::filesystem::status otherwise.

* If necessary, obtains the status of to, by no more than a single call to

* std::filesystem::symlink_status, if copy_options::skip_symlinks or
copy_options::create_symlinks is present in options;
* std::filesystem::status otherwise (including the case where
copy_options::copy_symlinks is present in options).

* If either from or to has an implementation-defined file type, the effects of
this function are implementation-defined.
* If from does not exist, reports an error.
* If from and to are the same file as determined by std::filesystem::equivalent,
reports an error
* If either from or to is not a regular file, a directory, or a symlink, as
determined by std::filesystem::is_other, reports an error
* If from is a directory, but to is a regular file, reports an error
* If from is a symbolic link, then

* If copy_options::skip_symlink is present in options, does nothing.
* Otherwise, if to does not exist and copy_options::copy_symlinks is
present in options, then behaves as if copy_symlink(from, to)
* Otherwise, reports an error

* Otherwise, if from is a regular file, then

* If copy_options::directories_only is present in options, does nothing
* Otherwise, if copy_options::create_symlinks is present in options,
creates a symlink to to. Note: from must be an absolute path unless to
is in the current directory.
* Otherwise, if copy_options::create_hard_links is present in options,
creates a hard link to to
* Otherwise, if to is a directory, then behaves as if copy_file(from,
to/from.filename(), options) (creates a copy of from as a file in the
directory to)
* Otherwise, behaves as if copy_file(from, to, options) (copies the file)

* Otherwise, if from is a directory and copy_options::create_symlinks is set in
options, reports an error with an error code equal to
std::make_error_code(std::errc::is_a_directory).
* Otherwise, if from is a directory and either options has copy_options::recursive
or is copy_options::none,

* If to does not exist, first executes create_directory(to, from)
(creates the new directory with a copy of the old directory's
attributes)
* Then, whether to already existed or was just created, iterates over the
files contained in from as if by for (const
std::filesystem::directory_entry& x :
std::filesystem::directory_iterator(from)) and for each directory
entry, recursively calls copy(x.path(), to/x.path().filename(), options
| in-recursive-copy), where in-recursive-copy is a special bit that has
no other effect when set in options. (The sole purpose of setting this
bit is to prevent recursive copying subdirectories if options is
copy_options::none.)

* Otherwise does nothing

Parameters

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

Return value

(none)

Exceptions

The overload that does not take a std::error_code& parameter throws
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. The overload taking a std::error_code& parameter sets it to
the OS API error code if an OS API call fails, and executes ec.clear() if no errors
occur. Any overload not marked noexcept may throw std::bad_alloc if memory
allocation fails.

Notes

The default behavior when copying directories is the non-recursive copy: the files
are copied, but not the subdirectories:

// Given
// /dir1 contains /dir1/file1, /dir1/file2, /dir1/dir2
// and /dir1/dir2 contains /dir1/dir2/file3
// After
std::filesystem::copy("/dir1", "/dir3");
// /dir3 is created (with the attributes of /dir1)
// /dir1/file1 is copied to /dir3/file1
// /dir1/file2 is copied to /dir3/file2

While with copy_options::recursive, the subdirectories are also copied, with their
content, recursively.

// ...but after
std::filesystem::copy("/dir1", "/dir3", std::filesystem::copy_options::recursive);
// /dir3 is created (with the attributes of /dir1)
// /dir1/file1 is copied to /dir3/file1
// /dir1/file2 is copied to /dir3/file2
// /dir3/dir2 is created (with the attributes of /dir1/dir2)
// /dir1/dir2/file3 is copied to /dir3/dir2/file3

Example

// Run this code

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

int main()
{
fs::create_directories("sandbox/dir/subdir");
std::ofstream("sandbox/file1.txt").put('a');
fs::copy("sandbox/file1.txt", "sandbox/file2.txt"); // copy file
fs::copy("sandbox/dir", "sandbox/dir2"); // copy directory (non-recursive)
const auto copyOptions = fs::copy_options::update_existing
| fs::copy_options::recursive
| fs::copy_options::directories_only
;
fs::copy("sandbox", "sandbox_copy", copyOptions);
static_cast<void>(std::system("tree"));
fs::remove_all("sandbox");
fs::remove_all("sandbox_copy");
}

Possible output:

.
├── sandbox
│ ├── dir
│ │ └── subdir
│ ├── dir2
│ ├── file1.txt
│ └── file2.txt
└── sandbox_copy
├── dir
│ └── subdir
└── dir2

8 directories, 2 files

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 3013 C++17 error_code overload marked noexcept but can noexcept removed
allocate memory
LWG 2682 C++17 attempting to create a symlink for a directory reports an error
succeeds but does nothing