Using std::setprecision to get the right precision for double to string conversion. #8302
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lucasmrod
reviewed
May 3, 2024
| @@ -23,7 +27,9 @@ class CastVisitor : public boost::static_visitor<std::string> { | |||
| } | |||
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| std::string operator()(const double& d) const { | |||
| std::string s{boost::lexical_cast<std::string>(d)}; | |||
| std::ostringstream ss; | |||
| ss << std::setprecision(std::numeric_limits<double>::digits10 + 1) << d; | |||
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Is it 16 because that's the case for most doubles?
Double values have between 15 and 18 digits of precision, with most double values having at least 16 significant digits. (source)
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SQLite supports 15 significant digits. So we set precision to 15 significant digits plus 1 insignificant (estimate). The previous approach was using more digits, leading to bad results in some cases.
This pattern is used in many other places:
https://github.com/search?q=%22std%3A%3Asetprecision%28std%3A%3Anumeric_limits%3Cdouble%3E%3A%3Adigits10+%2B+1%29%22&type=code
lucasmrod
approved these changes
May 3, 2024
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Fixes #8301
boost::lexical_cast was not using the right precision for double-to-string conversion.
Switched to using std::ostringstream.