How to Efficiently Concatenate a std::string and an int in C ?

Concatenating a std::string and an int

Combining a std::string and an int to form a single string can be a seemingly straightforward task, yet it may present some challenges. Let's tackle the given example:

std::string name = "John";
int age = 21;

To concatenate these elements into "John21," several approaches are available.

With Boost

Using Boost's lexical_cast, you can convert the int to a string and append it:

#include <boost/lexical_cast.hpp>

std::string result = name + boost::lexical_cast<std::string>(age);

With C 11

In C 11, the std::to_string function provides a convenient way to convert an int to a string:

std::string result = name + std::to_string(age);

With FastFormat

FastFormat offers both Format and Write methods for string concatenation:

#include <fastformat/format.hpp>
fastformat::fmt(result, "{0}{1}", name, age);
fastformat::write(result, name, age);

With the {fmt} library

The {fmt} library provides a concise syntax for string formatting:

#include <fmt/core.h>
std::string result = fmt::format("{}{}", name, age);

With IOStreams

Using an IO stream is a more verbose but standard C approach:

#include <sstream>

std::stringstream sstm;
sstm << name << age;
std::string result = sstm.str();

With itoa

Itoa (Integer-to-String) is a non-standard extension that converts an int to a string:

#include <stdlib.h>
char numstr[21]; // Ensure sufficient buffer size
std::string result = name + itoa(age, numstr, 10);

With sprintf

Sprintf is another non-standard extension that formats an int into a string:

#include <cstdio>
char numstr[21]; // Ensure sufficient buffer size
sprintf(numstr, "%d", age);
std::string result = name + numstr;

With STLSoft's integer_to_string

STLSoft provides a specialized function for converting an int to a string:

#include <stlsoft/string_algo.h>
char numstr[21]; // Ensure sufficient buffer size
std::string result = name + stlsoft::integer_to_string(numstr, 21, age);

With STLSoft's winstl::int_to_string

This function, specific to Windows, provides an efficient and safe conversion:

#include <stlsoft/winstl/int_to_string.hpp>
std::string result = name + winstl::int_to_string(age);

With Poco NumberFormatter

Poco's NumberFormatter can be used for formatting numbers as strings:

#include <Poco/NumberFormatter.h>
std::string result = name + Poco::NumberFormatter().format(age);

In summary, the chosen approach may vary depending on your specific requirements and platform. Consider performance, safety, and portability when selecting the most suitable solution for concatenating a std::string and an int.

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