Append an int to a std::string [duplicate]

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)); 

Answer 2

You cannot cast an int to a char* to get a string. Try this:

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

stringstream reference