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From: Thomas Koenig <tkoenig@netcologne.de>
Newsgroups: comp.compilers
Subject: Re: what is defined, was for or against equality
Date: Thu, 13 Jan 2022 11:17:13 -0000 (UTC)
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Thomas Koenig <tkoenig@netcologne.de> schrieb:

> [I have used Fortran systems that initialized otherwise undefined
> data to a value that would trap, to help find use-before-set errors.
> -John]

That usually is still available, but optional.  An short example:

$ cat a.f90
program main
  print *,a
end program main
$ gfortran -g -ffpe-trap=invalid -finit-real=snan a.f90
$ ./a.out

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

with a backtrace pointing to the offending line.

It does not necessarily work on COMMON blocks, though.