std::filesystem::copy_file

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"

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms 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

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)