Why Does Appending an Integer Directly to a std::string Lead to a Debug Assertion Fail?

Appending an Integer to a std::string: Why the Assertion Fails

In C , when attempting to append an integer value directly to a std::string as seen below:

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

you may encounter a Debug Assertion Fail. This occurs because the std::string::append() method requires its argument to be a NULL-terminated string (char*). However, passing an integer as a pointer to a character array without terminating it with a null character will result in undefined behavior and potentially a crash.

To correctly append an integer to a std::string, several approaches are available:

1. Using std::ostringstream:

#include <sstream>

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

This method creates a stringstream object, inserts the text and the integer value into it, and retrieves the resulting string.

2. Using std::to_string (C 11):

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

This approach uses the std::to_string function to convert the integer to a string and then performs the concatenation.

3. Using boost::lexical_cast:

#include <boost/lexical_cast.hpp>

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

This method utilizes the Boost library's lexical_cast function to convert the integer to a string and perform the concatenation.

The above is the detailed content of Why Does Appending an Integer Directly to a std::string Lead to a Debug Assertion Fail?. For more information, please follow other related articles on the PHP Chinese website!