How to Correctly Append an Integer to a String in C ?

Appending an Integer to a String in C

The std::string::append() method in C is used to append a character sequence or string to the existing string. However, it is essential to understand its behavior to avoid errors.

Consider the following code snippet:

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

This code attempts to append the ClientID integer to the query string. However, it throws a Debug Assertion Failure. The reason is that std::string::append() expects a char* argument that points to a null-terminated string.

Solutions:

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

• Using std::ostringstream:

#include <sstream>

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

• Using std::to_string (C 11 and later):

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

• Using boost::lexical_cast:

#include <boost/lexical_cast.hpp>

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

These methods ensure that the integer is correctly converted to a string before appending it to the query string, avoiding the Debug Assertion Failure.

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