Why Does Appending an Integer to a String in C Cause an Assertion Failure?

Appending an Integer to a String in C : Troubleshooting Assertion Failure

Consider the following code that attempts to append an integer to a string:

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

However, this code triggers a Debug Assertion Failure. To understand why, we need to examine the expected behavior of std::string::append().

std::string::append() takes a char* argument, which should be a NULL-terminated C-style string. However, in our case, we're passing a raw pointer to the integer ClientID, which is not a NULL-terminated string.

Solution Approaches

To append an integer to a string in C , you have several options:

1. std::ostringstream

#include <sstream>

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

2. std::to_string (C 11 and later)

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

3. Boost::lexical_cast

#include <boost/lexical_cast.hpp>

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

Each of these approaches will correctly convert the integer ClientID to a string and append it to the base string, producing a valid string without triggering an assertion failure.

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