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:

#include 
#include 

double pi = 3.14159265359;
std::stringstream stream;
stream 
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:
#include 
#include 

double pi = 3.14159265359;
std::array 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
}
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.