Fortran & C Interoperability
The ISO_C_BINDING intrinsic module and the BIND attribute introduced in Fortran 2003 are very handy for producing standard and portable Fortran code that interacts with C code. The example given here shows how to use the popen, fgets, and pclose routines from the C standard library to pipe the result of a shell command into a Fortran allocatable string.
module pipes_module
use,intrinsic :: iso_c_binding
implicit none
private
interface
function popen(command, mode) bind(C,name='popen')
import :: c_char, c_ptr
character(kind=c_char),dimension(*) :: command
character(kind=c_char),dimension(*) :: mode
type(c_ptr) :: popen
end function popen
function fgets(s, siz, stream) bind(C,name='fgets')
import :: c_char, c_ptr, c_int
type (c_ptr) :: fgets
character(kind=c_char),dimension(*) :: s
integer(kind=c_int),value :: siz
type(c_ptr),value :: stream
end function fgets
function pclose(stream) bind(C,name='pclose')
import :: c_ptr, c_int
integer(c_int) :: pclose
type(c_ptr),value :: stream
end function pclose
end interface
public :: c2f_string, get_command_as_string
contains
!**********************************************
! convert a C string to a Fortran string
!**********************************************
function c2f_string(c) result(f)
implicit none
character(len=*),intent(in) :: c
character(len=:),allocatable :: f
integer :: i
i = index(c,c_null_char)
if (i<=0) then
f = c
else if (i==1) then
f = ''
else if (i>1) then
f = c(1:i-1)
end if
end function c2f_string
!**********************************************
! return the result of the command as a string
!**********************************************
function get_command_as_string(command) result(str)
implicit none
character(len=*),intent(in) :: command
character(len=:),allocatable :: str
integer,parameter :: buffer_length = 1000
type(c_ptr) :: h
integer(c_int) :: istat
character(kind=c_char,len=buffer_length) :: line
str = ''
h = c_null_ptr
h = popen(command//c_null_char,'r'//c_null_char)
if (c_associated(h)) then
do while (c_associated(fgets(line,buffer_length,h)))
str = str//c2f_string(line)
end do
istat = pclose(h)
end if
end function get_command_as_string
end module pipes_module
A example use of this module is:
program test
use pipes_module
implicit none
character(len=:),allocatable :: res
res = get_command_as_string('uname')
write(*,'(A)') res
res = get_command_as_string('ls -l')
write(*,'(A)') res
end program test
References
- C interop to popen, comp.lang.fortran, 12/2/2009.