从两个绝对路径获得相对路径

path lexically_relative(const path& p) const

#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;
}

fs::path relativePath( const fs::path &path, const fs::path &relative_to )
{
    // create absolute paths
    fs::path p = fs::absolute(path);
    fs::path r = fs::absolute(relative_to);

    // if root paths are different, return absolute path
    if( p.root_path() != r.root_path() )
        return p;

    // initialize relative path
    fs::path result;

    // find out where the two paths diverge
    fs::path::const_iterator itr_path = p.begin();
    fs::path::const_iterator itr_relative_to = r.begin();
    while( itr_path != p.end() && itr_relative_to != r.end() && *itr_path == *itr_relative_to ) {
        ++itr_path;
        ++itr_relative_to;
    }

    // add \"../\" for each remaining token in relative_to
    if( itr_relative_to != r.end() ) {
        ++itr_relative_to;
        while( itr_relative_to != r.end() ) {
            result /= \"..\";
            ++itr_relative_to;
        }
    }

    // add remaining path
    while( itr_path != p.end() ) {
        result /= *itr_path;
        ++itr_path;
    }

    return result;
}

boost::filesystem

QDir dir(\"/home/bob\");
QString s;

s = dir.relativeFilePath(\"images/file.jpg\");     // s is \"images/file.jpg\"
s = dir.relativeFilePath(\"/home/mary/file.txt\"); // s is \"../mary/file.txt\"

std::filesystem::relative

#include <filesystem>
#include <iostream>
namespace fs = std::filesystem;
int main()
{
    const fs::path base(\"/is/the/speed/of/light/absolute\");
    const fs::path p(\"/is/the/speed/of/light/absolute/or/is/it/relative/to/the/observer\");
    const fs::path p2(\"/little/light/races/in/orbit/of/a/rogue/planet\");
    std::cout << \"Base is base: \" << fs::relative(p, base).generic_string() << \'\\n\'
              << \"Base is deeper: \" << fs::relative(base, p).generic_string() << \'\\n\'
              << \"Base is orthogonal: \" << fs::relative(p2, base).generic_string();
    // Omitting exception handling/error code usage for simplicity.
}

Base is base: or/is/it/relative/to/the/observer
Base is deeper: ../../../../../../..
Base is orthogonal: ../../../../../../little/light/races/in/orbit/of/a/rogue/planet

namespace fs = boost::filesystem;

bool GetCommonRoot(const fs::path& path1,
                       const fs::path& path2,
                       fs::path& routeFrom1To2,
                       std::vector<fs::path>& commonDirsInOrder)
{
   fs::path pathA( fs::absolute( path1));
   fs::path pathB( fs::absolute( path2));

   // Parse both paths into vectors of tokens. I call them \"dir\" because they\'ll
   // be the common directories unless both paths are the exact same file.
   // I also Remove the \".\" and \"..\" paths as part of the loops

   fs::path::iterator    iter;
   std::vector<fs::path> dirsA;
   std::vector<fs::path> dirsB;
   for(iter = pathA.begin(); iter != pathA.end(); ++iter) {
       std::string token = (*iter).string();
       if(token.compare(\"..\") == 0) {      // Go up 1 level => Pop vector
          dirsA.pop_back();
       }
       else if(token.compare(\".\") != 0) {  // \".\" means \"this dir\" => ignore it
          dirsA.push_back( *iter);
       }
   }
   for(iter = pathB.begin(); iter != pathB.end(); ++iter) {
       std::string token = (*iter).string();
       if(token.compare(\"..\") == 0) {      // Go up 1 level => Pop vector
          dirsB.pop_back();
       }
       else if(token.compare(\".\") != 0) {  // \".\" means \"this dir\" => ignore it
          dirsB.push_back( *iter);
       }
   }

   // Determine how far to check in each directory set
   size_t commonDepth = std::min<int>( dirsA.size(), dirsB.size());
   if(!commonDepth) {
       // They don\'t even share a common root- no way from A to B
       return false;
   }

   // Match entries in the 2 vectors until we see a divergence
   commonDirsInOrder.clear();
   for(size_t i=0; i<commonDepth; ++i) {
      if(dirsA[i].string().compare( dirsB[i].string()) != 0) {   // Diverged
         break;
      }
      commonDirsInOrder.push_back( dirsA[i]);  // I could use dirsB too.
   }

   // Now determine route: start with A
   routeFrom1To2.clear();
   for(size_t i=0; i<commonDepth; ++i) {
       routeFrom1To2 /= dirsA[i];
   }
   size_t backupSteps = dirsA.size() - commonDepth; // # of \"up dir\" moves we need
   for(size_t i=0; i<backupSteps; ++i) {
       routeFrom1To2 /= \"../\";
   }

   // Append B\'s path to go down to it from the common root
   for(size_t i=commonDepth; i<dirsB.size(); ++i) {
       routeFrom1To2 /= dirsB[i];    // ensures absolutely correct subdirs
   }
   return true;

os.path.relpath(to, from)

static inline bool StringsEqual_i(const std::string& lhs, const std::string& rhs)
{
    return _stricmp(lhs.c_str(), rhs.c_str()) == 0;
}

static void SplitPath(const std::string& in_path, std::vector<std::string>& split_path)
{
    size_t start = 0;
    size_t dirsep;
    do
    {
        dirsep = in_path.find_first_of(\"\\\\/\", start);
        if (dirsep == std::string::npos)
            split_path.push_back(std::string(&in_path[start]));
        else
            split_path.push_back(std::string(&in_path[start], &in_path[dirsep]));
        start = dirsep + 1;
    } while (dirsep != std::string::npos);
}

/**
 * Get the relative path from a base location to a target location.
 *
 * \\param to The target location.
 * \\param from The base location. Must be a directory.
 * \\returns The resulting relative path.
 */
static std::string GetRelativePath(const std::string& to, const std::string& from)
{
    std::vector<std::string> to_dirs;
    std::vector<std::string> from_dirs;

    SplitPath(to, to_dirs);
    SplitPath(from, from_dirs);

    std::string output;
    output.reserve(to.size());

    std::vector<std::string>::const_iterator to_it = to_dirs.begin(),
                                             to_end = to_dirs.end(),
                                             from_it = from_dirs.begin(),
                                             from_end = from_dirs.end();

    while ((to_it != to_end) && (from_it != from_end) && StringsEqual_i(*to_it, *from_it))
    {
         ++to_it;
         ++from_it;
    }

    while (from_it != from_end)
    {
        output += \"..\\\\\";
        ++from_it;
    }

    while (to_it != to_end)
    {
        output += *to_it;
        ++to_it;

        if (to_it != to_end)
            output += \"\\\\\";
    }

    return output;
}

std::string

std::vector

strAlgExeFile = helper.GetRelativePath(PathA, PathB);

PathB

strAlgExeFile = helper.GetRelativePath((helper.GetCurrentDir()).c_str(), strAlgExeFile.c_str());

#ifdef _WIN32                                                                              
    #define STR_TOKEN \"\\\\\"                                                                 
    #define LAST_FOLDER \"..\\\\\"                                                             
    #define FOLDER_SEP \"\\\\\"                                                                
    #define LINE_BREAK \"\\r\\n\"                                                              
#else                                                                                      
    #define STR_TOKEN \"/\"                                                                  
    #define LAST_FOLDER \"../\"                                                              
    #define FOLDER_SEP \"/\"                                                                 
    #define LINE_BREAK \"\\n\"                                                                
#endif // _WIN32                                                                           

void CHelper::SplitStr2Vec(const char* pszPath, vector<string>& vecString)                 
{                                                                                          
  char * pch;                                                                              

  pch = strtok (const_cast < char*> (pszPath), STR_TOKEN );                                
  while (pch != NULL)                                                                      
  {                                                                                        
    vecString.push_back( pch );                                                            
    pch = strtok (NULL, STR_TOKEN );                                                       
  }                                                                                        
}                                                                                          

string& CHelper::GetRelativePath(const char* pszPath1,const char* pszPath2)                
{                                                                                          
    vector<string> vecPath1, vecPath2;                                                     
    vecPath1.clear();                                                                      
    vecPath2.clear();                                                                      
    SplitStr2Vec(pszPath1, vecPath1);                                                      
    SplitStr2Vec(pszPath2, vecPath2);                                                      
    size_t iSize = ( vecPath1.size() < vecPath2.size() )? vecPath1.size(): vecPath2.size();
    unsigned int iSameSize(0);                                                             
    for (unsigned int i=0; i<iSize; ++i)                                                   
    {                                                                                      
        if ( vecPath1[i] != vecPath2[i])                                                   
        {                                                                                  
            iSameSize = i;                                                                 
            break;                                                                         
        }                                                                                  
    }                                                                                      

    m_strRelativePath = \"\";                                                                
    for (unsigned int i=0 ; i< (vecPath1.size()-iSameSize) ; ++i)                          
        m_strRelativePath += const_cast<char *> (LAST_FOLDER);                             

    for (unsigned int i=iSameSize ; i<vecPath2.size() ; ++i)                               
    {                                                                                      
        m_strRelativePath += vecPath2[i];                                                  
        if( i < (vecPath2.size()-1) )                                                      
            m_strRelativePath += const_cast<char *> (FOLDER_SEP);                          
    }                                                                                      

    return m_strRelativePath;                                                              
}