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# Not A Number - quick fix

I am using GNU C++ and Borland Builder C++

I have written a program, and discovered a fault - However I do not have the time to rewrite the whole program from the ground up as it will take too long. I wish to patch the code instead.

My program sometimes returns NaN becasue it has exceeded a boundary, my idea is to use a if statement to check to see if the return value is real number.

I believe that I need to use <math.h>

I have tried using :

if ( number == NAN)
{
Do this . .. .
}
else
{
Do that
}

However there is a compiler error NAN not declared.

Any suggestions

Cheers

Will Ryder
0
wjryder
1 Solution

Commented:
>>if ( number == NAN)

You'd better use

if ( isnan ( number)) {
}

ans comparing doubles for equality is not a good idea. 'isnan()' is declared in 'float.h'
0

Commented:
BTW - what you are looking for is '_Nan', and it can be found in 'ymath.h'...
0

Author Commented:
perhaps using finite is better as it will also catch infinity problems

0

Author Commented:
Is this a Borland compatiable function ?

can't find it  in the help file
0

Commented:
Try to look up '_isnan()' or '_isinf()' - the functions itself are IEEE, so they should be present in any compiler with floating point support...
0

Commented:
BTW, as you mentioned gcc also:

ISINF(3)            Linux Programmer's Manual            ISINF(3)

NAME
isinf,  isnan,  finite - test for infinity or not-a-number
(NaN)

SYNOPSIS
#include <math.h>

int isinf(double value);

int isnan(double value);

int finite(double value);

DESCRIPTION
The isinf() function returns -1 if value represents  nega-
tive  infinity,  1  if value represents positive infinity,
and 0 otherwise.

The isnan() function returns a non-zero value if value  is
"not-a-number" (NaN), and 0 otherwise.

The finite() function returns a non-zero value if value is
neither infinite nor a "not-a-number" (NaN) value,  and  0
otherwise.

CONFORMING TO
BSD 4.3
0

Commented:
For BCB a bit other:
_isNAN(double d)
_isNANl(long double ld)
to check if given floating-point value for not a
number (NAN).

0

Commented:
Why do they have to diversify these names?

gcc: isnan()
VC:  _isnan()
BCB: _isNAN()

Hmmpf....
0

Commented:
>>Why do they have to diversify these names?

VC is using the correct nameing convension.
According to the standards, any function that is part of the implementation, should start with an underscore, and proceed with a lowercase letter.

The GCC compiler should not be using isnan() with out the underscore prefix.
And it makes no sence to me why BCB would want to have a function that starts with a lower case letter, and then go upercase in the last part of the name.
BCB is not breaking the standards, but it certainly using a stupid naming convention.
0
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