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std::filesystem::copy_file - cppreference.com

1,2) The default, equivalent to (3,4) with copy_options::none used as options.

Copies a single file from

to

, using the copy options indicated by

. The behavior is undefined if there is more than one option in any of the

option group present in

(even in the groups not relevant to

).

• If !filesystem::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 filesystem::equivalent(from, to);
• to is not a regular file as determined by !filesystem::is_regular_file(to);
• none of the filesystem::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 filesystem::last_write_time().

The non-throwing overloads return false if an error occurs.

true if the file was copied, false otherwise.

Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

Throws

on underlying OS API errors, constructed with

as the first path argument,

as the second path argument, and the OS error code as the error code argument.

Sets a

parameter to the OS API error code if an OS API call fails, and executes

if no errors occur.

The functions involve at most one direct or indirect call to filesystem::status(to) (used both to determine if the file exists, and, for filesystem::copy_options::update_existing option, its last write time).

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

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

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

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

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