std::filesystem::copy_file

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Filesystem library

Classes
filesystem::path filesystem::filesystem_error filesystem::directory_entry filesystem::directory_iterator filesystem::recursive_directory_iterator filesystem::file_status	filesystem::space_info filesystem::file_type filesystem::perms filesystem::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::system_complete filesystem::canonical filesystem::copy filesystem::copy_file filesystem::copy_symlink filesystem::create_directory filesystem::create_directories filesystem::create_hard_link filesystem::create_symlink filesystem::create_directory_symlink filesystem::current_path filesystem::exists filesystem::equivalent	filesystem::file_size filesystem::hard_link_count filesystem::last_write_time filesystem::permissions filesystem::read_symlink filesystem::remove filesystem::remove_all filesystem::rename filesystem::resize_file filesystem::space filesystem::status filesystem::symlink_status filesystem::temp_directory_path
File types
filesystem::is_block_file filesystem::is_character_file filesystem::is_directory filesystem::is_empty filesystem::status_known	filesystem::is_fifo filesystem::is_other filesystem::is_regular_file filesystem::is_socket filesystem::is_symlink

 

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 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...

• If to and from are the same as determined by equivalent(from, to), report an error
• Otherwise, if none of the copy_file control options are set in options, report an error
• 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 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 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. This overload has

noexcept specification:  

noexcept

  

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.

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)