Fortran Wiki
FAQ (Rev #5)

Why does random_number return the same value each time I run my program?

How do I produce a library?

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?

See Floating point arithmetic.

How do I read until the end of a file (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)

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

See also: EOF idiom? on comp.lang.fortran.

How do I read a character without having to press enter?

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 has a section on "Reading single keystrokes from Fortran" which provides a couple of short C functions (sys_keyin.c) which can be called from Fortran to achive the desired behavior on most Unix systems.

See also: Get Key Function? on comp.lang.fortran.

Fortran Wiki FAQ (Rev #5)