Append an int to a std::string

Question

Why is this code gives an Debug Assertion Fail?

   std::string query;
   int ClientID = 666;
   query = "select logged from login where id = ";
   query.append((char *)ClientID);

Answer 1

The std::string::append() method expects its argument to be a NULL terminated string (char*).

There are several approaches for producing a string containg an int:

• std::ostringstream

  #include <sstream>
  
  std::ostringstream s;
  s << "select logged from login where id = " << ClientID;
  std::string query(s.str());
  

• std::to_string (C++11)

  std::string query("select logged from login where id = " +
                    std::to_string(ClientID));
  

• boost::lexical_cast

  #include <boost/lexical_cast.hpp>
  
  std::string query("select logged from login where id = " +
                    boost::lexical_cast<std::string>(ClientID));