How Do You Precisely Convert Floats to Strings with Specified Decimal Precision in C ?

Precise Conversion of Floats to Strings with Specified Decimal Precision

In C , converting a floating-point number to a string with specific precision and decimal digits requires careful consideration. This guide explores two common solutions: stringstream and the to_chars function from C 17.

Using Stringstream

Stringstream is a versatile tool for manipulating strings in C . To convert a float to a string with specified precision, stream manipulators can be applied:

<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();

• std::fixed ensures the number is represented in fixed-point notation, with a decimal point and specified number of digits.
• std::setprecision(2) controls the number of decimal places to be displayed.

Using to_chars Function (C 17 and above)

For more technical purposes, such as writing data to XML or JSON, the to_chars function introduced in C 17 offers a concise solution:

<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>

• The std::to_chars function takes a buffer (in std::array form), a number, and a format specification (in this case, std::chars_format::fixed with 2 decimal places).
• If the conversion is successful, the resulting string is constructed from the buffer.

By employing these techniques, you can convert floats to strings in C with precise control over the number of decimal digits, ensuring that your data is represented accurately and in accordance with your requirements.

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