// Simple test program to demonstrate a failure to 'loopback' or 'round trip'
// double to and from a stream, here std::stringstream
// but possibly, even probably, ALL streams, including cout and cin?

// This shows a single example, but some further tests with random values
// have shown that most failures occur in a narrow range, about 0.0001 to 0.005.
// About one value in three is a single bit 'wrong' in these ranges.

// Although the C++ Standard is not quite explicit whether this should
// return exactly the same value, it is extremely desirable.

// For example, Boost lexical_cast and Boost.serialization use the process below.
// If one serializes and restores, then checks will (have!) revealed this difference.
// Much more seriously, repeated serialization and de-serialization will add
// one bit to some values on each trip causing the value to drift, and
// an exquisitely difficult/impossible debugging task.

// An exhaustive test using ALL float values, the results are exact.
// For double, this is not possible in a useful time ;-)

// Copyright Paul A. Bristow 1998-2006.

// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)

// pbristow@hetp.u-net.com

#include <iostream>
  using std::cout;
  using std::endl;
#include <sstream>
	using std::stringstream;
#include <cassert>

int main ()
{
	double output_value = 0.00010000433948393407;
	cout.precision(17); // max_digits10 for double.
	stringstream stream;
	stream.precision(17); // max_digits10 for double.
	stream << output_value; // write out.
	double read_value;
	stream >> read_value; // read back.
	assert(read_value == output_value); // in debug mode only (of course!).
	if (read_value != output_value) // so can test in release mode too.
	{
		cout << "output_value " << output_value << " != read_value "  << read_value << endl;
	}
} // main



/*

Both compiled with VS 8.0, including a post-build autorun.

------ Build started: Project: loopback2, Configuration: Debug Win32 ------
Compiling...
loopback2.cpp
Linking...
Embedding manifest...
Autorun "j:\Cpp\Misc\debug\loopback2.exe" 
Assertion failed: read_value == output_value, file j:\cpp\misc\loopback2\loopback2.cpp, line 42
Project : error PRJ0019: A tool returned an error code from "Autorun "j:\Cpp\Misc\debug\loopback2.exe" "
Build Time 0:06
Build log was saved at "file://j:\Cpp\Misc\loopback2\Debug\BuildLog.htm"
loopback2 - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

------ Build started: Project: loopback2, Configuration: Release Win32 ------
Compiling...
loopback2.cpp
Linking...
Generating code
Finished generating code
Embedding manifest...
Autorun "j:\Cpp\Misc\release\loopback2.exe" 
output_value 0.00010000433948393407 != read_value 0.00010000433948393406
Build Time 0:02
Build log was saved at "file://j:\Cpp\Misc\loopback2\Release\BuildLog.htm"
loopback2 - 0 error(s), 0 warning(s)
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========


*/