boost::文件系统获取相对路径

在新版本的boost（从 1.60 开始）中，您可以使用 boost::filesystem::relative .（请参阅此处的文档。

#include <boost/filesystem.hpp>
#include <iostream>
namespace fs = boost::filesystem;
int main()
{
    fs::path parentPath("/home/user1/");
    fs::path childPath("/home/user1/Downloads/Books");
    fs::path relativePath = fs::relative(childPath, parentPath);
    std::cout << relativePath << std::endl;
}

提供答案中的代码在每一行上都很长。假设你写了namespace fs = boost::filesystem;那么这段代码可以让你大部分时间，对我来说看起来更容易阅读：

    auto relativeTo( const fs::path& from, const fs::path& to )
    {
       // Start at the root path and while they are the same then do nothing then when they first
       // diverge take the entire from path, swap it with '..' segments, and then append the remainder of the to path.
       auto fromIter = from.begin();
       auto toIter = to.begin();
       // Loop through both while they are the same to find nearest common directory
       while( fromIter != from.end() && toIter != to.end() && *toIter == *fromIter )
       {
          ++toIter;
          ++fromIter;
       }
       // Replace from path segments with '..' (from => nearest common directory)
       auto finalPath = fs::path{};
       while( fromIter != from.end() )
       {
          finalPath /= "..";
          ++fromIter;
       }
       // Append the remainder of the to path (nearest common directory => to)
       while( toIter != to.end() )
       {
          finalPath /= *toIter;
          ++toIter;
       }
       return finalPath;
    }

取自以下链接，通过以下链接找到 Nicol：

template < >
    path& path::append< typename path::iterator >( typename path::iterator begin, typename path::iterator end, const codecvt_type& cvt)
    { 
        for( ; begin != end ; ++begin )
            *this /= *begin;
        return *this;
    }
    // Return path when appended to a_From will resolve to same as a_To
    boost::filesystem::path make_relative( boost::filesystem::path a_From, boost::filesystem::path a_To )
    {
        a_From = boost::filesystem::absolute( a_From ); a_To = boost::filesystem::absolute( a_To );
        boost::filesystem::path ret;
        boost::filesystem::path::const_iterator itrFrom( a_From.begin() ), itrTo( a_To.begin() );
        // Find common base
        for( boost::filesystem::path::const_iterator toEnd( a_To.end() ), fromEnd( a_From.end() ) ; itrFrom != fromEnd && itrTo != toEnd && *itrFrom == *itrTo; ++itrFrom, ++itrTo );
        // Navigate backwards in directory to reach previously found base
        for( boost::filesystem::path::const_iterator fromEnd( a_From.end() ); itrFrom != fromEnd; ++itrFrom )
        {
            if( (*itrFrom) != "." )
                ret /= "..";
        }
        // Now navigate down the directory branch
        ret.append( itrTo, a_To.end() );
        return ret;
    }

将其粘贴在头文件中，它应该可以执行您想要的操作。

示例调用：

boost::filesystem::path a("foo/bar"), b("foo/test/korv.txt");
std::cout << make_relative( a, b ).string() << std::endl;

遗憾的是，这样的函数在 Boost.File 系统中不存在。有人要求，但他们似乎并不在乎。

您基本上必须手动完成。

Boost.Filesystem 1.60 添加了可用于处理此问题的relative函数。

从 C++17 开始，此问题的解决方案是对存在的路径使用 std：：filesystem：：relative 对存在的路径使用 std：：：filesystem：:p ath：：lexically_relative。

#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;
fs::path path("/home/user1/Downloads/Books");
fs::path base("/home/user1/");
std::cout << fs::relative(path, base) << 'n';
std::cout << path.lexically_relative(base) << 'n';

这打印

"Downloads/Books"
"Downloads/Books"

接受答案的代码不起作用。它应该是

namespace boost { namespace filesystem {
template <> path& path::append<path::iterator>(path::iterator begin, path::iterator end, const codecvt_type& cvt)
{
    for( ; begin != end ; ++begin )
        *this /= *begin;
    return *this;
}
// Return path when appended to a_From will resolve to same as a_To
boost::filesystem::path make_relative( boost::filesystem::path a_From, boost::filesystem::path a_To )
{
    a_From = boost::filesystem::absolute( a_From ); a_To = boost::filesystem::absolute( a_To );
    boost::filesystem::path ret;
    boost::filesystem::path::const_iterator itrFrom( a_From.begin() ), itrTo( a_To.begin() );
    // Find common base
    for( boost::filesystem::path::const_iterator toEnd( a_To.end() ), fromEnd( a_From.end() ) ; itrFrom != fromEnd && itrTo != toEnd && *itrFrom == *itrTo; ++itrFrom, ++itrTo );
    // Navigate backwards in directory to reach previously found base
    for( boost::filesystem::path::const_iterator fromEnd( a_From.end() ); itrFrom != fromEnd; ++itrFrom )
    {
        if( (*itrFrom) != "." )
            ret /= "..";
    }
    // Now navigate down the directory branch
    ret.append( itrTo, a_To.end() );
    return ret;
}
} } // namespace boost::filesystem