[SOLVED] Floating point exception when reading real values from an input file

Floating point exception when reading real values from an input file

I try to read a float value from an input file in Fortran.

To do so I use this code :

...
INTEGER            :: nf
REAL               :: re

OPEN(newunit=nf, file='toto.txt')

READ(unit=nf, fmt=*) re
...

with toto.txt a text file containing my real value :

10.1001 ! this value is supposed to be read by the Fortran program

If I compile and execute like this, everything works well.

But I get some trouble when I compile and execute with fpe option. I have a error at the readding line that looks like:

Program received signal SIGFPE: Floating-point exception - erroneous arithmetic operation

Backtrace for this error
#0  0xfffffff
#1  0xfffffff
...

I use a gfortran command : gfortran -g1 -c -fbacktrace -ffpe-trap=invalid,zero,overflow,underflow,inexact,denormal -Wall -fcheck=all my_prog.f90

I assume my read action is not proper. So is that error normal? Is there a proper way to read real values?

Solution

The floating point exceptions inexact and denormal happen way too often and during legitimate use of floating point arithmetic is inexact. Almost all real-world floating point arithmetic. Even reading a single number from file or keyboard, because not all decimal numbers can be stored exactly in binary. Denormal happens slightly less often, but the use can still be legitimate.

Therefore it is not useful to trap these floating point exceptions. Even underflow is debatable. I would not trap it by default, but I can see its usefulness.