to_chars()

template<typename FloatType >

JSON_HEDLEY_RETURNS_NON_NULL char * nlohmann::detail::to_chars	(	char *	first,
		const char *	last,
		FloatType	value
	)

generates a decimal representation of the floating-point number value in [first, last).

The format of the resulting decimal representation is similar to printf's g format. Returns an iterator pointing past-the-end of the decimal representation.

Note

The input number must be finite, i.e. NaN's and Inf's are not supported.

The buffer must be large enough.

The result is NOT null-terminated.

Definition at line 16546 of file json.hpp.

{
    static_cast<void>(last); // maybe unused - fix warning
    JSON_ASSERT(std::isfinite(value));
 
    // Use signbit(value) instead of (value < 0) since signbit works for -0.
    if (std::signbit(value))
    {
        value = -value;
        *first++ = '-';
    }
 
#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wfloat-equal"
#endif
 
    if (value == 0) // +-0
    {
        *first++ = '0';
        // Make it look like a floating-point number (#362, #378)
        *first++ = '.';
        *first++ = '0';
        return first;
    }
 
#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif
    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
    // Compute v = buffer * 10^decimal_exponent.
    // The decimal digits are stored in the buffer, which needs to be interpreted
    // as an unsigned decimal integer.
    // len is the length of the buffer, i.e. the number of decimal digits.
    int len = 0;
    int decimal_exponent = 0;
    dtoa_impl::grisu2(first, len, decimal_exponent, value);
    JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
    // Format the buffer like printf("%.*g", prec, value)
    constexpr int kMinExp = -4;
    // Use digits10 here to increase compatibility with version 2.
    constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
    JSON_ASSERT(last - first >= kMaxExp + 2);
    JSON_ASSERT(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
    return dtoa_impl::format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
}