C++: How do I ignore the first directory path when comparing paths in boost::filesystem?

Question

I'm trying to compare two directories and find what files are different inside. So I'm using a boost::filesystem::recursive_directory_iterator to add all contents of each directory to respective vectors. Then I sort each vector alphabetically and start comparing paths. The problem is it's including the 'base' path and I don't want that, example:

Version1/Assets/info.txt

Version2/Assets/info.txt

Those paths are comparing different, but I want them to compare the same. To clarify, I'm not even checking the binaries yet, just the path name so far. I'd to compare them like this:

/Assets/info.txt

I've been browsing through the boost documentation for a couple hours and I'm convinced there must be an elegant solution for my problem. I realize I could have solved this a while ago by getting a substring of what I want, but there must be a less ugly way.

Answer 1

The boost::filesystem::recursive_directory_iterator has a path() property that you can query. You can then use the following decomposition methods available for boost::filesystem::path to manually build the path to compare:

path  root_path() const; 
path  root_name() const;         // returns 0 or 1 element path
path  root_directory() const;    // returns 0 or 1 element path
path  relative_path() const;
path  parent_path() const;
path  filename() const;          // returns 0 or 1 element path
path  stem() const;              // returns 0 or 1 element path
path  extension() const;         // returns 0 or 1 element path

For example you can rollout a version of stripping the root as follows:

#include <iostream>
#include <boost/filesystem.hpp>

boost::filesystem::path strip_root(const boost::filesystem::path& p) {
    const boost::filesystem::path& parent_path = p.parent_path();
    if (parent_path.empty() || parent_path.string() == "/")
        return boost::filesystem::path();
    else
        return strip_root(parent_path) / p.filename();
}

int main() {
    std::cout << strip_root("/a") << std::endl;
    std::cout << strip_root("/a/b") << std::endl;
    std::cout << strip_root("/a/b/c") << std::endl;
    std::cout << strip_root("/a/b.dir/c.ext") << std::endl;    
}
// Output:
""
"b"
"b/c"
"b.dir/c.ext"

Answer 2

I think I have cleaner solution:

fs::path stripFirstDir(fs::path p)
{
    p = p.relative_path();
    if (p.empty()) return {};
    return p.lexically_relative(*p.begin());
}

https://godbolt.org/z/hr3hcr