Move utility function to module.

Author: interkosmos

examples/pipeline.f90

@@ -18,6 +18,7 @@ program main
     !! ```
     use :: nng
     use :: nng_pipeline0
+    use :: nng_util
     implicit none (type, external)
 
     character(80) :: message, name, url
@@ -32,14 +33,6 @@ program main
         case default; print '("Usage: pipeline node0|node1 <URL> <ARG> ...")'
     end select
 contains
-    pure function f_c_str(f_str) result(c_str)
-        !! In Fortran 2023, use `f_c_string()` instead.
-        character(*), intent(in)  :: f_str
-        character(:), allocatable :: c_str
-
-        c_str = trim(f_str) // c_null_char
-    end function f_c_str
-
     subroutine fatal(rc, str)
         integer,      intent(in) :: rc
         character(*), intent(in) :: str

src/nng_util.f90

@@ -8,6 +8,7 @@ module nng_util
     private
 
     public :: c_f_str_ptr
+    public :: f_c_str
 contains
     subroutine c_f_str_ptr(c_str, f_str)
         !! Copies a C string, passed as a C pointer, to a Fortran string.
@@ -44,4 +45,15 @@ end function c_strlen
 
         if (.not. allocated(f_str)) f_str = ''
     end subroutine c_f_str_ptr
+
+    pure function f_c_str(f_str) result(c_str)
+        !! Converts Fortran string to C string. In Fortran 2023, use
+        !! `f_c_string()` instead.
+        use, intrinsic :: iso_c_binding, only: c_null_char
+
+        character(*), intent(in)  :: f_str
+        character(:), allocatable :: c_str
+
+        c_str = trim(f_str) // c_null_char
+    end function f_c_str
 end module nng_util