c++/7369: weird results with the statement "#define PI 4.*atan(1.)"
pel@ucla.edu
pel@ucla.edu
Sun Jul 21 12:46:00 GMT 2002
>Number: 7369
>Category: c++
>Synopsis: weird results with the statement "#define PI 4.*atan(1.)"
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Sun Jul 21 12:06:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Peter Latham
>Release: 2.96
>Organization:
>Environment:
Red Hat Linux 7.3
>Description:
If PI is defined via the statement
#define PI 4.*atan(1.)
then 1/PI and 1/3.14159 are different.
>How-To-Repeat:
compile using "g++ main.c". then type "a.out", which
prints PI, 1/PI and 1/3.14159. the result is
3.141593 0.196350 0.318310
If for some strange reasont the file didn't attach properly,
the source code is:
#include <stdio.h>
#include <math.h>
#define PI 4.*atan(1.)
//#define PI 3.14159
void main(int argc, char** argv)
{
fprintf(stdout, "%f %f %f\n", PI, 1/PI, 1/3.14159);
}
>Fix:
the workaround is to not use atan in the define statement,
#define PI=3.14159
this produces the correct output.
>Release-Note:
>Audit-Trail:
>Unformatted:
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