How Do You Convert a Float to a String with Precision and Number of Decimal Digits in C ?

How to Convert a Float to a String with Precision and Number of Decimal Digits in C

In C , you can convert a float to a string while specifying the precision and number of decimal digits using various methods, including:

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();

In this approach, std::fixed ensures fixed-point notation, and std::setprecision sets the number of decimal places.

Using std::to_chars (C 17)

For specific technical conversions, C 17 introduced the std::to_chars function:

<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>

Here, std::chars_format::fixed specifies fixed-point notation, and the third parameter controls the number of decimal places.

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