diff --git a/toml/get.hpp b/toml/get.hpp
index 20944f4..1cf15ba 100644
--- a/toml/get.hpp
+++ b/toml/get.hpp
@@ -182,9 +182,10 @@ T get(const value& v)
     T container;
     if(ar.size() != container.size())
     {
-        throw std::out_of_range(detail::format_error_for_value(v, concat_to_string(
+        throw std::out_of_range(detail::format_underline(concat_to_string(
             "[erorr] toml::get specified container size is ", container.size(),
-            " but there are ", ar.size(), " elements in toml array."), "here"));
+            " but there are ", ar.size(), " elements in toml array."),
+            detail::get_region(v), "here"));
     }
     std::transform(ar.cbegin(), ar.cend(), container.begin(),
                    [](const value& x){return ::toml::get<value_type>(x);});
@@ -204,9 +205,9 @@ T get(const value& v)
     const auto& ar = v.cast<value_t::Array>();
     if(ar.size() != 2)
     {
-        throw std::out_of_range(detail::format_error_for_value(v, concat_to_string(
+        throw std::out_of_range(detail::format_underline(concat_to_string(
             "[erorr] toml::get specified std::pair but there are ", ar.size(),
-            " elements in toml array."), "here"));
+            " elements in toml array."), detail::get_region(v), "here"));
     }
     return std::make_pair(::toml::get<first_type >(ar.at(0)),
                           ::toml::get<second_type>(ar.at(1)));
@@ -234,10 +235,10 @@ T get(const value& v)
     const auto& ar = v.cast<value_t::Array>();
     if(ar.size() != std::tuple_size<T>::value)
     {
-        throw std::out_of_range(detail::format_error_for_value(v, concat_to_string(
+        throw std::out_of_range(detail::format_underline(concat_to_string(
             "[erorr] toml::get specified std::tuple with ",
             std::tuple_size<T>::value, "elements, but there are ", ar.size(),
-            " elements in toml array."), "here"));
+            " elements in toml array."), detail::get_region(v), "here"));
     }
     return detail::get_tuple_impl<T>(ar,
             detail::make_index_sequence<std::tuple_size<T>::value>{});
@@ -312,9 +313,9 @@ find(const toml::value& v, const toml::key& ky)
     const auto& tab = ::toml::get<toml::table>(v);
     if(tab.count(ky) == 0)
     {
-        throw std::out_of_range(detail::format_error_for_value(v,
-            concat_to_string("[error] key \"", ky, "\" not found"),
-            concat_to_string("in this table")));
+        throw std::out_of_range(detail::format_underline(concat_to_string(
+            "[error] key \"", ky, "\" not found"), detail::get_region(v),
+            "in this table"));
     }
     return ::toml::get<T>(tab.at(ky));
 }
@@ -325,9 +326,9 @@ find(toml::value& v, const toml::key& ky)
     auto& tab = ::toml::get<toml::table>(v);
     if(tab.count(ky) == 0)
     {
-        throw std::out_of_range(detail::format_error_for_value(v,
-            concat_to_string("[error] key \"", ky, "\" not found"),
-            concat_to_string("in this table")));
+        throw std::out_of_range(detail::format_underline(concat_to_string(
+            "[error] key \"", ky, "\" not found"), detail::get_region(v),
+            "in this table"));
     }
     return ::toml::get<T>(tab.at(ky));
 }
@@ -338,9 +339,9 @@ find(toml::value&& v, const toml::key& ky)
     auto tab = ::toml::get<toml::table>(std::move(v));
     if(tab.count(ky) == 0)
     {
-        throw std::out_of_range(detail::format_error_for_value(v,
-            concat_to_string("[error] key \"", ky, "\" not found"),
-            concat_to_string("in this table")));
+        throw std::out_of_range(detail::format_underline(concat_to_string(
+            "[error] key \"", ky, "\" not found"), detail::get_region(v),
+            "in this table"));
     }
     return ::toml::get<T>(std::move(tab[ky]));
 }
diff --git a/toml/parser.hpp b/toml/parser.hpp
index a965e1e..d6859b4 100644
--- a/toml/parser.hpp
+++ b/toml/parser.hpp
@@ -6,6 +6,7 @@
 #include "lexer.hpp"
 #include "types.hpp"
 #include "value.hpp"
+#include <iostream>
 #include <cstring>
 
 namespace toml
diff --git a/toml/value.hpp b/toml/value.hpp
index 8b98ca1..ca5b653 100644
--- a/toml/value.hpp
+++ b/toml/value.hpp
@@ -17,8 +17,8 @@ namespace toml
 
 namespace detail
 {
-std::string // forward decl
-format_error_for_value(const value&, const std::string&, const std::string&);
+// to show error messages. not recommended for users.
+region_base const& get_region(const value&);
 }// detail
 
 template<typename T>
@@ -555,14 +555,8 @@ class value
         }
     }
 
-    std::string
-    format_error(const std::string& msg, const std::string& com) const
-    {
-        return detail::format_underline(msg, *(this->region_info_), com);
-    }
-
-    friend std::string detail::format_error_for_value(
-            const value&, const std::string&, const std::string&);
+    // for error messages
+    friend region_base const& detail::get_region(const value&);
 
     template<value_t T>
     struct switch_cast;
@@ -594,10 +588,9 @@ class value
 
 namespace detail
 {
-inline std::string format_error_for_value(
-        const value& v, const std::string& m, const std::string& c)
+inline region_base const& get_region(const value& v)
 {
-    return v.format_error(m, c);
+    return *(v.region_info_);
 }
 }// detail
 
@@ -668,8 +661,8 @@ typename detail::toml_default_type<T>::type& value::cast() &
 {
     if(T != this->type_)
     {
-        throw type_error(this->format_error(concat_to_string(
-            "[error] toml::value bad_cast to ", T),
+        throw type_error(format_underline(concat_to_string(
+            "[error] toml::value bad_cast to ", T), *region_info_,
             concat_to_string("the actual type is ", this->type_)));
     }
     return switch_cast<T>::invoke(*this);
@@ -679,8 +672,8 @@ typename detail::toml_default_type<T>::type const& value::cast() const&
 {
     if(T != this->type_)
     {
-        throw type_error(this->format_error(concat_to_string(
-            "[error] toml::value bad_cast to ", T),
+        throw type_error(format_underline(concat_to_string(
+            "[error] toml::value bad_cast to ", T), *region_info_,
             concat_to_string("the actual type is ", this->type_)));
     }
     return switch_cast<T>::invoke(*this);
@@ -690,8 +683,8 @@ typename detail::toml_default_type<T>::type&&      value::cast() &&
 {
     if(T != this->type_)
     {
-        throw type_error(this->format_error(concat_to_string(
-            "[error] toml::value bad_cast to ", T),
+        throw type_error(format_underline(concat_to_string(
+            "[error] toml::value bad_cast to ", T), *region_info_,
             concat_to_string("the actual type is ", this->type_)));
     }
     return switch_cast<T>::invoke(std::move(*this));