How can I copy a directory using Boost Filesystem

Question

How can I copy a directory using Boost Filesystem? I have tried boost::filesystem::copy_directory() but that only creates the target directory and does not copy the contents.

Vessel

boost::filesystem::copy will copy directories or files alike. You can write a recursive algorithm that copies the directory and files within using that. – Delvecchio

Ah. Thank you. I'm surprise that this isn't part of boost::filesystem. Also I couldn't find any documentation in the Boost library website that said in English what the function copy_directory actually does. – Vessel

Answer 1

bool copyDir(
    boost::filesystem::path const & source,
    boost::filesystem::path const & destination
)
{
    namespace fs = boost::filesystem;
    try
    {
        // Check whether the function call is valid
        if(
            !fs::exists(source) ||
            !fs::is_directory(source)
        )
        {
            std::cerr << "Source directory " << source.string()
                << " does not exist or is not a directory." << '\n'
            ;
            return false;
        }
        if(fs::exists(destination))
        {
            std::cerr << "Destination directory " << destination.string()
                << " already exists." << '\n'
            ;
            return false;
        }
        // Create the destination directory
        if(!fs::create_directory(destination))
        {
            std::cerr << "Unable to create destination directory"
                << destination.string() << '\n'
            ;
            return false;
        }
    }
    catch(fs::filesystem_error const & e)
    {
        std::cerr << e.what() << '\n';
        return false;
    }
    // Iterate through the source directory
    for(
        fs::directory_iterator file(source);
        file != fs::directory_iterator(); ++file
    )
    {
        try
        {
            fs::path current(file->path());
            if(fs::is_directory(current))
            {
                // Found directory: Recursion
                if(
                    !copyDir(
                        current,
                        destination / current.filename()
                    )
                )
                {
                    return false;
                }
            }
            else
            {
                // Found file: Copy
                fs::copy_file(
                    current,
                    destination / current.filename()
                );
            }
        }
        catch(fs::filesystem_error const & e)
        {
            std:: cerr << e.what() << '\n';
        }
    }
    return true;
}

Usage:

copyDir(boost::filesystem::path("/home/nijansen/test"), boost::filesystem::path("/home/nijansen/test_copy")); (Unix)

copyDir(boost::filesystem::path("C:\\Users\\nijansen\\test"), boost::filesystem::path("C:\\Users\\nijansen\\test2")); (Windows)

As far as I see, the worst that can happen is that nothing happens, but I won't promise anything! Use at your own risk.

Please note that the directory you're copying to must not exist. If directories within the directory you are trying to copy can't be read (think rights management), they will be skipped, but the other ones should still be copied.

Update

Refactored the function respective to the comments. Furthermore the function now returns a success result. It will return false if the requirements for the given directories or any directory within the source directory are not met, but not if a single file could not be copied.

Delvecchio

If you use C++ you, should use std::cerr instead of fprintf and stderr. And also, since this is Boost.Filesystem, you should use boost::path instead of std::string. – Leitmotif

Thanks for the suggestions, I improved the function accordingly. – Delvecchio

Note that you still have to be careful of what you're copying where. If you ran copyDir(boost::filesystem::path("."), boost::filesystem::path("test")), it will copy itself until it is terminated because the path length exceeds the limit, or you run out of disk space. – Delvecchio

Thank you very much nijansen, that fits very neatly into what I am doing. I am copying a very well defined and known folder to another location so I don't need to worry about any special cases. I'm still surprised that copy_directory doesn't copy the contents or at least have an option to copy contents. – Vessel

Instead of doing dest.string() + "/" you should use the / operator. dest / current.filename() – Legalism

nice tipp, arsenm. didn't know about the / operator, even works with a string as second argument. makes it much more readable! – Tricyclic

Answer 2

Since C++17 you don't need boost for this operation anymore as filesystem has been added to the standard.

Use std::filesystem::copy

#include <exception>
#include <filesystem>
namespace fs = std::filesystem;

int main()
{
    fs::path source = "path/to/source/folder";
    fs::path target = "path/to/target/folder";

    try {
        fs::copy(source, target, fs::copy_options::recursive);
    }
    catch (std::exception& e) { // Not using fs::filesystem_error since std::bad_alloc can throw too.
        // Handle exception or use error code overload of fs::copy.
    }
}

See also std::filesystem::copy_options.

Reincarnation

Many thanks Roi. I hope visitors notice your answer. – Vessel

Note this was added to ISO C++ in C++ 17. – Abeokuta

Answer 3

I see this version as an improved upon version of @nijansen's answer. It also supports the source and/or destination directories to be relative.

namespace fs = boost::filesystem;

void copyDirectoryRecursively(const fs::path& sourceDir, const fs::path& destinationDir)
{
    if (!fs::exists(sourceDir) || !fs::is_directory(sourceDir))
    {
        throw std::runtime_error("Source directory " + sourceDir.string() + " does not exist or is not a directory");
    }
    if (fs::exists(destinationDir))
    {
        throw std::runtime_error("Destination directory " + destinationDir.string() + " already exists");
    }
    if (!fs::create_directory(destinationDir))
    {
        throw std::runtime_error("Cannot create destination directory " + destinationDir.string());
    }

    for (const auto& dirEnt : fs::recursive_directory_iterator{sourceDir})
    {
        const auto& path = dirEnt.path();
        auto relativePathStr = path.string();
        boost::replace_first(relativePathStr, sourceDir.string(), "");
        fs::copy(path, destinationDir / relativePathStr);
    }
}

The main differences are exceptions instead of return values, the use of recursive_directory_iterator and boost::replace_first to strip the common part of the iterator path, and relying on boost::filesystem::copy() to do the right thing with different file types (preserving symlinks, for instance).

Paddlefish

+1 for prefering exceptions over boolean return values. Also, relativePathStr can be computed using path.lexically_relative(sourceDir), which may be simpler to read than boost::replace_first. – Tome

Answer 4

This is a non-Boost version I'm using based on Doineann's code. I'm using std::filesystem but couldn't use a simple fs::copy(src, dst, fs::copy_options::recursive); because I wanted to filter which files are copied by file extension inside the loop.

void CopyRecursive(fs::path src, fs::path dst)
{
    //Loop through all the dirs
    for (auto dir : fs::recursive_directory_iterator(src))
    {
        //copy the path's string to store relative path string
        std::wstring relstr = dir.path().wstring();

        //remove the substring matching the src path
        //this leaves only the relative path
        relstr.erase(0, std::wstring(src).size());

        //combine the destination root path with relative path
        fs::path newFullPath = dst / relstr;

        //Create dir if it's a dir
        if (fs::is_directory(newFullPath))
        {
            fs::create_directory(newFullPath);
        }

        //copy the files
        fs::copy(dir.path(), newFullPath, fs::copy_options::recursive | fs::copy_options::overwrite_existing);
    }
}

relstr.erase(0, std::wstring(src).size()); is a working Boost-less replacement for the boost::replace_first() call used in the other answer

Bybidder

Answer 5

Example program in C++ using Boost libraries to copy the contents of one directory to another directory:

#include <boost/filesystem.hpp>

namespace fs = boost::filesystem;

int main()
{
    fs::path source_dir("path/to/source/directory");
    fs::path destination_dir("path/to/destination/directory");
    try
    {
        // Check if source directory exists
        if (!fs::exists(source_dir))
        {
            std::cerr << "Source directory does not exist." << std::endl;
            return 1;
        }
        // Check if destination directory exists, if not create it
        if (!fs::exists(destination_dir))
        {
            fs::create_directory(destination_dir);
        }
        // Iterate over all the files in the source directory
        for (fs::directory_iterator file(source_dir); file != fs::directory_iterator(); ++file)
        {
            // Copy file to destination directory
            fs::copy_file(file->path(), destination_dir / file->path().filename(), fs::copy_option::overwrite_if_exists);
        }
    }
    catch (fs::filesystem_error const& e)
    {
        std::cerr << "Error copying directory: " << e.what() << std::endl;
    }
    return 0;
}

In this program, we use Boost's filesystem library to access and manipulate files and directories. The program checks if the source directory exists, create the destination directory if it does not exist, and then iterates over all the files in the source directory and copies each file to the destination directory using fs::copy_file() function. The fs::copy_option::overwrite_if_exists flag is used to overwrite existing files in the destination directory.

Kessel