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copied!<p>As of version <a href="http://www.boost.org/doc/libs/1_60_0/libs/filesystem/doc/reference.html" rel="nofollow noreferrer">1.60.0</a> boost.filesystem does support this. You're looking for the member function <code>path lexically_relative(const path& p) const</code>.</p> <p>Original, pre-1.60.0 answer below.</p> <hr> <p>Boost doesn't support this; it's an open issue — <a href="https://svn.boost.org/trac/boost/ticket/1976" rel="nofollow noreferrer">#1976 (Inverse function for complete)</a> — that nevertheless doesn't seem to be getting much traction.</p> <p>Here's a vaguely naive workaround that seems to do the trick (not sure whether it can be improved):</p> <pre><code>#include <boost/filesystem/path.hpp> #include <boost/filesystem/operations.hpp> #include <boost/filesystem/fstream.hpp> #include <stdexcept> /** * https://svn.boost.org/trac/boost/ticket/1976#comment:2 * * "The idea: uncomplete(/foo/new, /foo/bar) => ../new * The use case for this is any time you get a full path (from an open dialog, perhaps) * and want to store a relative path so that the group of files can be moved to a different * directory without breaking the paths. An IDE would be a simple example, so that the * project file could be safely checked out of subversion." * * ALGORITHM: * iterate path and base * compare all elements so far of path and base * whilst they are the same, no write to output * when they change, or one runs out: * write to output, ../ times the number of remaining elements in base * write to output, the remaining elements in path */ boost::filesystem::path naive_uncomplete(boost::filesystem::path const p, boost::filesystem::path const base) { using boost::filesystem::path; using boost::filesystem::dot; using boost::filesystem::slash; if (p == base) return "./"; /*!! this breaks stuff if path is a filename rather than a directory, which it most likely is... but then base shouldn't be a filename so... */ boost::filesystem::path from_path, from_base, output; boost::filesystem::path::iterator path_it = p.begin(), path_end = p.end(); boost::filesystem::path::iterator base_it = base.begin(), base_end = base.end(); // check for emptiness if ((path_it == path_end) || (base_it == base_end)) throw std::runtime_error("path or base was empty; couldn't generate relative path"); #ifdef WIN32 // drive letters are different; don't generate a relative path if (*path_it != *base_it) return p; // now advance past drive letters; relative paths should only go up // to the root of the drive and not past it ++path_it, ++base_it; #endif // Cache system-dependent dot, double-dot and slash strings const std::string _dot = std::string(1, dot<path>::value); const std::string _dots = std::string(2, dot<path>::value); const std::string _sep = std::string(1, slash<path>::value); // iterate over path and base while (true) { // compare all elements so far of path and base to find greatest common root; // when elements of path and base differ, or run out: if ((path_it == path_end) || (base_it == base_end) || (*path_it != *base_it)) { // write to output, ../ times the number of remaining elements in base; // this is how far we've had to come down the tree from base to get to the common root for (; base_it != base_end; ++base_it) { if (*base_it == _dot) continue; else if (*base_it == _sep) continue; output /= "../"; } // write to output, the remaining elements in path; // this is the path relative from the common root boost::filesystem::path::iterator path_it_start = path_it; for (; path_it != path_end; ++path_it) { if (path_it != path_it_start) output /= "/"; if (*path_it == _dot) continue; if (*path_it == _sep) continue; output /= *path_it; } break; } // add directory level to both paths and continue iteration from_path /= path(*path_it); from_base /= path(*base_it); ++path_it, ++base_it; } return output; } </code></pre>

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