Question

I have a database in PostgreSQL. And I have sql query (which btw works great in PostgreSQL, so the sql code isn’t wrong):

SELECT COUNT(*) as size, creation_date FROM item INNER JOIN raf_item USING (id) INNER JOIN item_detail USING (id) GROUP BY creation_date;

where creation date is defined as creation_date Date; in PostgreSQL.The query returns, for example (depends on what I have in my database):

size | creation_date
21   | 12-31-2012
18   | 04-03-2002

I’m using SOCI + C++ to get data from this query. My whole C++ code:

#include <iostream>
#include <cstdlib>
#include <soci.h>
#include <string>
#include <postgresql/soci-postgresql.h>
using namespace std;

bool connectToDatabase(soci::session &sql, string databaseName, string user, string password)
{
    try
    {
        sql.open(soci::postgresql, "dbname=" +databaseName + " user="+user + " password="+password);
    }
    catch (soci::postgresql_soci_error const & e)
    {
        cerr << "PostgreSQL error: " << e.sqlstate() << " " << e.what() << std::endl;
        return false;
    }
    catch (std::exception const & e)
    {
        cerr << "Some other error: " << e.what() << std::endl;
        return false;
    }
    return true;
}

void getDataFromDatabase(soci::session &sql)
{
    soci::row r;
    sql << "select count(*) as size, creation_date from item inner join raf_item using (id) inner join item_detail using (id) group by creation_date;", soci::into(r);
    for(std::size_t i = 0; i != r.size(); ++i)
    {
        cout << r.get<int>(i);
        tm when = r.get<tm>(i);
        cout << asctime(&when);
    }
}

int main(int argc, char **argv)
{
    soci::session sql;
    bool success = connectToDatabase(sql, "testdb", "testuser", "pass");
    if (success)
    {
        cout << "Connected.\n";
        getDataFromDatabase(sql);
    }

    else
        cout << "Not connected.\n";
    return 0;
}

But I got this error, when I tried to run the application (compilation is fine) :

terminate called after throwing an instance of ‘std::bad_cast’
what(): std::bad_cast Interrupt (core dumped)

Please help, when the compilation is fine I really don’t know how to fix this.

Maybe the problem is that creation_date is DATE and tm keeps also time … ? If so, how to fix this?

Answer 1

While you did solve your question, the code you posted is more a workaround than the real solution for the problem.

Your problem is, that COUNT(*) returns a value of bigint (or int8) type, as described here,
and soci converts bigint to a long long int type, as described in this chart. If the types do not match excatly, a bad_cast exception will be thrown.

Therefore, the code in your question should be cout << r.get<long long>(i); to avoid the bad_cast exception.