< cpp‎ | experimental‎ | fs
Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals 2 TS)
Extensions for parallelism (parallelism TS)
Extensions for concurrency (concurrency TS)
Concepts (concepts TS)
Ranges (ranges TS)
Special mathematical functions (special math TR)
Defined in header <experimental/filesystem>
void copy( const path& from, const path& to );
void copy( const path& from, const path& to, error_code& ec );
(1) (filesystem TS)
void copy( const path& from, const path& to, copy_options options );
void copy( const path& from, const path& to, copy_options options, error_code& ec );
(2) (filesystem TS)

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, which is not relevant to copy)

The behavior is as follows:

  • First, before doing anything else, obtains type and permissions of from by no more than single call to status (or, if copy_options::skip_symlinks or copy_options::create_symlinks are present in options, by a call to symlink_status).
  • If necessary, obtains the status of to the same way, by no more than a single status or symlink_status call.
  • If from does not exist, reports an error.
  • If from and to are the same file as determined by equivalent(), reports an error
  • If either from or to is not a regular file, a directory, or a symlink, as determined by 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 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 directory_entry& x : directory_iterator(from)) and for each directory entry, recursively calls copy(x.path(), to/x.path().filename(), options | unspecified), where unspecified is some unspecified set of copy options.
  • Otherwise does nothing


[edit] 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

[edit] Return value


[edit] Exceptions

The overload that does not take a error_code& parameter throws filesystem_error on underlying OS API errors, constructed with from as the first argument, to as the second argument, and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking a 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. This overload has
noexcept specification:  

[edit] 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::experimental::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::experimental::filesystem::copy("/dir1", "/dir3", 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

[edit] Example

#include <iostream>
#include <fstream>
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;
int main()
    fs::copy("sandbox/file1.txt", "sandbox/file2.txt"); // copy file
    fs::copy("sandbox/dir", "sandbox/dir2"); // copy directory (non-recursive)
    // sandbox holds 2 files and 2 directories, one of which has a subdirectory
    // sandbox/file1.txt
    // sandbox/file2.txt
    // sandbox/dir2
    // sandbox/dir
    //    sandbox/dir/subdir
    fs::copy("sandbox", "sandbox/copy", fs::copy_options::recursive);
    // sandbox/copy holds copies of the above files and subdirectories

[edit] See also

specifies semantics of copy operations
(enum) [edit]
copies a symbolic link
(function) [edit]
copies file contents
(function) [edit]