# std::filesystem::copy_file

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< cpp‎ | filesystem

Defined in header `<filesystem>` |  |
bool copy_file( const std::filesystem::path& from, const std::filesystem::path& to ); bool copy_file( const std::filesystem::path& from, const std::filesystem::path& to, std::error_code& ec ); | (1) | (since C++17)
bool copy_file( const std::filesystem::path& from, const std::filesystem::path& to, std::filesystem::copy_options options ); bool copy_file( const std::filesystem::path& from, const std::filesystem::path& to, std::filesystem::copy_options options, std::error_code& ec ); | (2) | (since C++17)

1) The default, equivalent to (2) with `copy_options::none` used as `options`
2) 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 `copy_file`)

- If `!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 `equivalent(from, to)`;
    - `to` is not a regular file as determined by `!is_regular_file(to)`
    - none of the `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 `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

The overload that does not take a std::error_code& parameter throws `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 functions involve at most one direct or indirect call to `status(to)` (used both to determine if the file exists, and, for `copy_options::update_existing` option, its last write time)

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

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

### 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 allocate memory | noexcept removed

### Examples

Run this code

    #include <fstream>
    #include <iostream>
    #include <filesystem>
    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"

### See also

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

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