How to Precisely Convert a Float to a String with Controlled Precision and Digits?

Precise Float to String Conversion with Precision and Digits Control

In C , converting a float to a string involves specifying the precision and number of decimal digits, ensuring accurate representation.

Using Stringstream:

A common approach is using stringstream:

<code class="cpp">#include <iomanip>
#include <sstream>

double pi = 3.14159265359;
std::stringstream stream;
stream << std::fixed << std::setprecision(2) << pi;
std::string s = stream.str();

Fixed Formatting and Setprecision:

• fixed: Ensures fixed-point notation where floating-point values display with a specific number of decimal places.
• setprecision: Specifies the number of decimal digits to retain.

C 17 to_chars Family:

For technical conversions, C 17 introduces the to_chars family:

<code class="cpp">#include <array>
#include <charconv>

double pi = 3.14159265359;
std::array<char, 128> buffer;
auto [ptr, ec] = std::to_chars(buffer.data(), buffer.data() + buffer.size(), pi,
                               std::chars_format::fixed, 2);
if (ec == std::errc{}) {
    std::string s(buffer.data(), ptr);
    // ....
}
else {
    // error handling
}</code>

With this method, the conversion returns a string with the specified precision and digits, enabling accurate representation for both general and technical applications.

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