从版本1.60.0 boost.filesystem 开始支持这一点。您正在寻找成员函数path lexically_relative(const path& p) const。
下面是 1.60.0 之前的原始答案。
Boost 不支持这个；这是一个悬而未决的问题——#1976 (Inverse function for complete)——但似乎并没有引起太大的关注。
这是一个模糊的、幼稚的解决方法，似乎可以解决问题（不确定是否可以改进）：
#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;
}