std::filesystem::copy_file

 

C++

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Filesystem library (C++17)

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Technical specifications

Symbols index

External libraries

 

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::perm_options filesystem::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::canonicalfilesystem::weakly_canonical filesystem::relativefilesystem::proximate 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 filesystem::copy_file)

• 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.

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::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 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.

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"

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

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)