Re: [boost] [serialization] Serialisation/deserialisation offloating-point values

From: Paul Giaccone (paulg_at_[hidden])
Date: 2006-03-15 06:06:05

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