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

Barbara Streisand
Release: 2024-11-10 10:19:02
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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);
Copy after login

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());
Copy after login

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));
Copy after login

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));
Copy after login

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

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