For a straightforward conversion to std::string, use std::to_string(value). For floating-point values that need controlled formatting, use std::format in C++20 or later. For output into a caller-owned buffer without allocation, use std::to_chars in C++17 or later. The right choice depends on the output you need and the C++ standard-library support in your toolchain.
Choose the conversion method that matches your output
| Need | Use | What it returns or does |
|---|---|---|
| A simple numeric conversion to a string | std::to_string |
Returns a std::string; available since C++11. Floating-point output behavior changes in C++26. cppreference: std::to_string |
| Control over precision or notation | std::format |
Returns a formatted string; available since C++20. cppreference: std::format |
| Write into a supplied buffer without allocating | std::to_chars |
Writes characters to a buffer and reports the result; available since C++17. cppreference: std::to_chars |
Use std::to_string for a simple conversion
Include <string> and pass the number to std::to_string. Integer and floating-point overloads have been available since C++11.
#include <string>
int main() {
int count = 42;
std::string text = std::to_string(count); // "42"
}For floating-point values, be aware of the language-version difference. Before C++26, the function behaves as if it used fixed printf-style formatting. That commonly means six digits after the decimal point: 23.43 can become 23.430000, and a small nonzero value such as 1e-9 can become 0.000000. Before C++26, this formatting also relies on the current C locale. Since C++26, the reference describes the behavior as equivalent to std::format("{}", value). cppreference: std::to_string
Use std::format when the text needs specific formatting
In C++20 or later, include <format> and specify how the value should appear. For example, {:.2f} requests fixed notation with two digits after the decimal point.
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#include <format>
#include <string>
int main() {
double value = 23.43;
std::string text = std::format("{:.2f}", value); // "23.43"
}For general notation with six significant digits, use {:.6g}. With no explicit presentation or precision, the default floating-point presentation aims for a shortest round-trippable representation. By contrast, f, e, and g presentations default to precision six if you omit the precision. cppreference: format specification
Use std::to_chars to write into a buffer
Since C++17, std::to_chars in <charconv> can convert a value directly into a character range. It does not allocate, throw, or depend on locale. The result contains an end pointer and an error status; the written characters are not NUL-terminated.
#include <charconv>
#include <string>
int main() {
int value = 42;
char buffer[32];
auto result = std::to_chars(buffer, buffer + sizeof buffer, value);
if (result.ec == std::errc{}) {
std::string text(buffer, result.ptr); // "42"
}
}On success, the converted range is [buffer, result.ptr). Constructing a string from that range uses the returned end pointer rather than assuming a terminating NUL. If the supplied range is too small, the status is std::errc::value_too_large. cppreference: std::to_chars
Floating-point output with to_chars
Floating-point overloads support fixed, scientific, general, and hexadecimal formats, including overloads with explicit precision. The default representation aims to produce the shortest sequence that the corresponding std::from_chars implementation can parse to recover the value exactly. This round-trip guarantee applies to the matching conversion functions from the same implementation. cppreference: std::to_chars
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The standard-version labels identify when these facilities were added, but do not guarantee that every installed compiler and standard-library combination supports them. Check your project’s language mode, library implementation, and relevant feature-test macros before relying on std::format or std::to_chars. Support for a particular setup depends on the toolchain version and configuration.
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