why cant I use dbstl::map<string, int> in Berkeley DB C++?

i use C++, Berkeley DB 18.1.40 STL and Visual Studio 2015. i include libraries through the project settings i cant use dbstl::map<string, int> and get an error, but with dbstl::map<string, string> everything works

My code:

#define _CRT_SECURE_NO_WARNINGS
#pragma comment(lib, "libdb181.lib")
#pragma comment(lib, "libdb_stl181.lib")

#include "stdafx.h"
#include <iostream>
#include <dbstl_map.h>
#include <vector>
using namespace std;

int main(){
    const char* db_name = "db";
    const char* db_home_dir = "dirdb";

    DbEnv env(DB_CXX_NO_EXCEPTIONS);
    Db* pdb;

    try {
        dbstl::dbstl_startup();

        env.set_error_stream(&cerr);
        env.open(db_home_dir, DB_CREATE | DB_INIT_MPOOL, 0);

        pdb = new Db(&env, DB_CXX_NO_EXCEPTIONS);
        pdb->open(NULL, db_name, NULL, DB_BTREE, DB_CREATE, 0);

        /* STRING */

        typedef dbstl::db_map<string, string> dbmap_string;
        dbmap_string map_string(pdb, &env);
        string key_string = "string";
        string value_string = "its string!";
        map_string.insert({ key_string, value_string });

        string outvalue_string = map_string[key_string];
        cout << "key: " << key_string << endl << "value: " << outvalue_string << endl << endl;

        /* INT */
        
        typedef dbstl::db_map<string, u_int32_t> dbmap_int;
        dbmap_int map_digit(pdb, &env);

        string key_digit = "digit";
        u_int32_t value_digit = 5;
        map_digit.insert({ key_digit, value_digit });

        dbstl::dbstl_exit();

        if (pdb != NULL) {
            pdb->close(0);
            delete pdb;
        }
        env.close(0);

    

    }
    catch (DbException& e) {
        cerr << "DbException: " << e.what() << endl;
        return -1;
    }
    catch (std::exception& e) {
        cerr << e.what() << endl;
        return -1;
    }

    cout << "hello";
    _sleep(5000);
    return 0;
}

i get error:

Error C2516 'ddt': is not a legal base class ConsoleApplication8 c:\users\kordi\desktop\db18.1.40\lang\cxx\stl\dbstl_element_ref.h 58

1>c:\users\kordi\desktop\db-18.1.40\lang\cxx\stl\dbstl_element_ref.h(58): error C2516: 'ddt': is not a legal base class
1>  C:\Users\kordi\Desktop\db-18.1.40\lang\cxx\stl\dbstl_map.h(727): note: see declaration of 'ddt'
1>  C:\Users\kordi\Desktop\db-18.1.40\lang\cxx\stl\dbstl_map.h(727): note: see reference to class template instantiation 'dbstl::ElementRef<ddt>' being compiled
1>          with
1>          [
1>              ddt=u_int32_t
1>          ]
1>  C:\Users\kordi\Desktop\db-18.1.40\lang\cxx\stl\dbstl_map.h(1148): note: see reference to class template instantiation 'dbstl::db_map_iterator<kdt,ddt,value_type_sub>' being compiled
1>          with
1>          [
1>              kdt=std::string,
1>              ddt=u_int32_t,
1>              value_type_sub=dbstl::ElementRef<u_int32_t>
1>          ]
1>  ConsoleApplication8.cpp(55): note: see reference to class template instantiation 'dbstl::db_map<std::string,u_int32_t,dbstl::ElementRef<ddt>,dbstl::db_map_iterator<kdt,ddt,value_type_sub>>' being compiled
1>          with
1>          [
1>              ddt=u_int32_t,
1>              kdt=std::string,
1>              value_type_sub=dbstl::ElementRef<u_int32_t>
1>          ]

why am i getting this error? can i fix it?

You ended up using an ElementRef instead of an ElementHolder in the u_int32_t case.

• "The ElementHolder class is used to store primitive types [like u_int32_t, my edit] into STL containers"
• "The ElementRef class is used to store other types into STL containers".

Inheriting from u_int32_t like the ElementRef does in your case is never going to work. It should have been an ElementHolder<u_int32_t>.

You need to change your map containing a primitive type:

typedef dbstl::db_map<string, ElementHolder<u_int32_t>> dbmap_int;
//                            ^^^^^^^^^^^^^^^^^^^^^^^^

This also seems in line with the examples and documentation @ docs.oracle.com

The ElementHolder class template should be used for every type of dbstl container that will store C++ primitive data types, such as int, float, char *, wchar_t *, and so forth.