In C++ using ptree from boost, I need to find the relative key to access a.b.c2.e1 from a.b. This key is c2.e1. How can I write a function which finds this relative key?
#include
#include
#include
using namespace boost::property_tree;
std::string relative_key(const ptree &p1,const ptree &p2)
{
??????????????
// return "b.c2.e1";
}
int main()
{
ptree pt0;
pt0.put("a.b.c1",4);
pt0.put("a.b.c2.e1",4);
pt0.put("a.b.c4",4);
pt0.put("a.d",4);
pt0.put("k.m",4);
pt0.put("k.n",4);
ptree &pt_e1=pt0.get_child("a.b.c2.e1");
ptree &pt_b=pt0.get_child("a.b");
std::cout<
return 0;
}
解决方案
You'd need to write a recursive search function, like:
bool find_subtree_helper(ptree const& haystack, ptree const& needle, path_type& path) {
if (std::addressof(haystack) == std::addressof(needle))
return true;
for (auto& child : haystack) {
auto next = path;
next /= child.first;
if ( std::addressof(child.second) == std::addressof(needle)
|| find_subtree_helper(child.second, needle, next))
{
path = next;
return true;
}
}
return false;
}
path_type find_subtree(ptree const& haystack, ptree const& needle) {
path_type path;
if (!find_subtree_helper(haystack, needle, path))
throw std::range_error("not subtree");
return path;
}
Use it like:
path_type p = find_subtree(pt_b, pt_e1);
std::cout << p.dump() << std::endl;
Which prints "c2.e1".
Full Listing
#include
#include
#include
using namespace boost::property_tree;
using path_type = ptree::path_type;
bool find_subtree_helper(ptree const& haystack, ptree const& needle, path_type& path) {
if (std::addressof(haystack) == std::addressof(needle))
return true;
for (auto& child : haystack) {
auto next = path;
next /= child.first;
if ( std::addressof(child.second) == std::addressof(needle)
|| find_subtree_helper(child.second, needle, next))
{
path = next;
return true;
}
}
return false;
}
path_type find_subtree(ptree const& haystack, ptree const& needle) {
path_type path;
if (!find_subtree_helper(haystack, needle, path))
throw std::range_error("not subtree");
return path;
}
int main()
{
ptree pt0;
pt0.put("a.b.c1",4);
pt0.put("a.b.c2.e1",4);
pt0.put("a.b.c4",4);
pt0.put("a.d",4);
pt0.put("k.m",4);
pt0.put("k.n",4);
ptree &pt_e1 = pt0.get_child("a.b.c2.e1");
ptree &pt_b = pt0.get_child("a.b");
path_type p = find_subtree(pt_b, pt_e1);
std::cout << p.dump() << std::endl;
}