Paul A Bristow wrote:
If you want to test round-tripping on your platform and std lib without actually using serialization,
may I suggest a loop including something like:
double a = some start value; double aa; // to hold the read back.
std::stringstream s; s.precision(2+std::numeric_limits<double>::digits * 3010/10000); // cout << "output " << a; s << a; // output to string s //cout << ", s.str() is " << s.str(); s >> aa; // read back in. //cout << ", read back " << aa << endl; if (a != aa) { cout << "error " << a << tab << aa << endl; } a = nextafter(a, std::numeric_limits<double>::max()); // Make one bit bigger?
[...]
This should give you a feel for the risk of failure.
Paul
Funnily enough, I've just written a program to test the value I originally posted about (below, followed by its output): #include <string> #include <sstream> #include <iostream> #include <iomanip> #include <limits> int main(void) { const double orig_value = 0.0019075645054089487; std::stringstream stream; double num; stream << std::setprecision(2 + std::numeric_limits<double>::digits * 3030/10000); stream << orig_value; stream >> num; if (num == orig_value) { std::cout << "Match" << std::endl; } else { std::cout << "Deserialisation error" << std::endl; std::cout << std::setprecision(2 + std::numeric_limits<double>::digits * 3030/10000); std::cout << "Original numerical value: " << orig_value << std::endl; std::cout << "Contents of stream: " << stream.str() << std::endl; std::cout << "Deserialised value: " << num << std::endl; } return 0; } Output: Deserialisation error Original numerical value: 0.0019075645054089487 Contents of stream: 0.0019075645054089487 Deserialised value: 0.0019075645054089489 This is the same result as in my original thread, so it does indeed look like a Microsoft issue with redirection (>>), not with serialisation itself. Paul