I have this code:

float number=getFloat();
assert(number!=float.nan); //this passes
assert(to!(char[])(number)!="nan"); //this fails
writefln(string.toString(number)); //this outputs: "nan"
writefln( to!(char[])(to!(long)(number)) ); //this generates an error

What did I do wrong?

Reply to acarion,

> I have this code:
> 
> float number=getFloat();
> assert(number!=float.nan); //this passes

IIRC this will also pass:

assert(float.nan != float.nan);

this is because D used IEEE floating point semantics. Under IEEE a comparison with NaN will always be  not equal

If you want to test for nan use "testedValue !<>= 0"* or the isnan function

> assert(to!(char[])(number)!="nan"); //this fails
> writefln(string.toString(number)); //this outputs: "nan"
> writefln( to!(char[])(to!(long)(number)) ); //this generates an error
> What did I do wrong?
> 

* this is the not grater than, less than, or equal to operator.

BCS wrote:
> Reply to acarion,
> 
>> I have this code:
>>
>> float number=getFloat();
>> assert(number!=float.nan); //this passes
> 
> IIRC this will also pass:
> 
> assert(float.nan != float.nan);
> 
> this is because D used IEEE floating point semantics. Under IEEE a comparison with NaN will always be  not equal
> 
> If you want to test for nan use "testedValue !<>= 0"* or the isnan function

You can also use (x!=x) to test to see if x is NaN, and (x==x) to make
sure it is not NaN.

	-- Daniel

On 10/7/07, BCS <ao@pathlink.com> wrote:
> If you want to test for nan use "testedValue !<>= 0"

Are we really sure about that?

If testedValue is complex (with non-zero real part) then it will not be less than 0, it will not be greater than zero, and it will not be equal to zero. But it will also not be NaN.

Janice Caron wrote:
> On 10/7/07, BCS <ao@pathlink.com> wrote:
>> If you want to test for nan use "testedValue !<>= 0"
> 
> Are we really sure about that?
> 
> If testedValue is complex (with non-zero real part) then it will not
> be less than 0, it will not be greater than zero, and it will not be
> equal to zero. But it will also not be NaN.

I believe you'd get a type error in that case (real and creal can't be directly compared, etc.)  Haven't tried it though.

Thanks,
Nathan Reed

BCS wrote:
> Reply to acarion,
> 
>> I have this code:
>>
>> float number=getFloat();
>> assert(number!=float.nan); //this passes
> 
> IIRC this will also pass:
> 
> assert(float.nan != float.nan);
> 
> this is because D used IEEE floating point semantics. Under IEEE a comparison with NaN will always be  not equal
> 
> If you want to test for nan use "testedValue !<>= 0"* or the isnan function

I tend to use:

testedValue !<>= testedValue

Though I've occasionally wondered whether the 'is' identity operator should work for checking against nan:

testedValue is float.nan



Sean