FAQ in Fortran Wiki

### Why does [[random_number]] return the same value each time I run my program? {: #random_seed }
### How do I produce a library? {: #libraries }
To build a static library `libfoo.a` containing all
modules and procedures in the `.f90` files in the
current directory on Linux:
 % gfortran -c *.f90
 % ar cr libfoo.a *.o
The first command builds the object files and the
second archives the object files into a static archive.
To build a shared library `libfoo.so`:
 % gfortran -shared *.f90 -o libfoo.so -fPIC
In both cases, other compiler flags such as `-O2` can
be used.
### Why doesn't `u == 1.4D0` work? {: #fp-equality }
See [[Floating point arithmetic]].
### How do I read until the end of a file (EOF)? {: #eof }
A common [[Fortran 95]] idiom for reading lines until the
end of file is
 integer :: stat
 character(len=100) :: buf
 open(15, file='foo.txt')
 do
 read(fh, iostat=stat) buf
 if (stat /= 0) exit
 ! process buf
 end do
 close(15)
{: lang=fortran }
This example catches all conditions, not just the end of file.
To specifically catch the EOF in [[Fortran 2003]] one can use
the [[iso_fortran_env]] module and replace the `if` condition
above with
 if (stat == iostat_end) exit
{: lang=fortran }
See also:
[EOF idiom?](http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/149d94a68d30fba3)
on [[comp lang fortran|comp.lang.fortran]].
### How do I read a character without having to press enter? {: #getkey }
There isn't a portable way to do this either in Fortran or C,
in short, because the terminal controls when the input is sent
to your program and by default it is buffered. You must request
that the terminal send each key and the method for doing so is
platform-dependent.
[Clive Page's Fortran Resources](http://www.star.le.ac.uk/~cgp/fortran.html)
has a section on "Reading single keystrokes from Fortran" which provides
a couple of short C functions
([sys_keyin.c](http://www.star.le.ac.uk/~cgp/sys_keyin.c))
which can be called from Fortran to
achive the desired behavior on most Unix systems.
See also: [Get Key Function?](http://groups.google.com/groups?threadm=edf0a73b-ff05-4849-90f6-2aa93445d388@v35g2000pro.googlegroups.com)
on [[comp lang fortran|comp.lang.fortran]].
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## See Also
* [The Fortran FAQ](http://www.faqs.org/faqs/fortran-faq/)