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std::filesystem::copy_file

From cppreference.com
 
 
 
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 ) noexcept;
(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 ) noexcept;
(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:
  • 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.

Contents

[edit] Parameters

from - path to the source file
to - path to the target file
ec - out-parameter for error reporting in the non-throwing overload

[edit] Return value

true if the file was copied, false otherwise.

[edit] 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.

[edit] 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.

[edit] Examples

#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"

[edit] See also

specifies semantics of copy operations
(enum) [edit]
copies a symbolic link
(function) [edit]
(C++17)
copies files or directories
(function) [edit]