From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Brian O'Kennedy
Sent: Wednesday, April 07, 2010 3:16 PM
To: Boost-users@lists.boost.org
Subject: [Boost-users] [Boost.Test] Floating point NAN comparison

Hi, 

This bit of Boost.Test code fails:

//////////////////////////////////////////////////////////////////////

BOOST_AUTO_TEST_CASE( nantest )

{

  float a,b;

  a = b = 1.0;

  BOOST_CHECK_EQUAL( a, b );  // passes

  a = b = NAN;

  BOOST_CHECK_EQUAL( a, b );  // fails

}

//////////////////////////////////////////////////////////////////////

The failure is because, by definition, NAN != NAN. What I'm after is a test macro which takes this into account and will pass the equality test when both elements are NAN. 

BOOST_CHECK_CLOSE has the same behaviour.  Is the best solution to write my own custom predicate? 

You can use the TR1 bool isnan(a) function in the boost.math to check for NaNness.

\boost-sandbox\math_toolkit\libs\math\example\fpclassify.cpp gives some examples of

using boost::math::isnan;

\boost_1_42_0\libs\math\test\test_classify.cpp(68): BOOST_CHECK_EQUAL((::boost::math::isnan)(t), false);

gives some examples of using boost.test with NaNs

See the boost_pdf_1_41_0/math.pdf for details.

HTH

Paul

---

Paul A. Bristow

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Kendal, UK   LA8 8AB

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pbristow@hetp.u-net.com