gfortran.texi (Interoperability with C): Fix ordering in menu and add new subsection about pointers.

2010-08-10  Daniel Kraft  <d@domob.eu>

	* gfortran.texi (Interoperability with C): Fix ordering in menu
	and add new subsection about pointers.
	(Interoperable Subroutines and Functions): Split off the pointer part.
	(working with Pointers): New subsection with extended discussion
	of pointers (especially procedure pointers).

From-SVN: r163073
This commit is contained in:
Daniel Kraft 2010-08-10 17:40:59 +02:00 committed by Daniel Kraft
parent f6aa1e0fe3
commit da4dbc2518
2 changed files with 141 additions and 9 deletions

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@ -1,3 +1,11 @@
2010-08-10 Daniel Kraft <d@domob.eu>
* gfortran.texi (Interoperability with C): Fix ordering in menu
and add new subsection about pointers.
(Interoperable Subroutines and Functions): Split off the pointer part.
(working with Pointers): New subsection with extended discussion
of pointers (especially procedure pointers).
2010-08-09 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/44235

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@ -1933,10 +1933,11 @@ and their use is highly recommended.
@menu
* Intrinsic Types::
* Further Interoperability of Fortran with C::
* Derived Types and struct::
* Interoperable Global Variables::
* Interoperable Subroutines and Functions::
* Working with Pointers::
* Further Interoperability of Fortran with C::
@end menu
Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a
@ -2059,7 +2060,8 @@ matches the Fortran declaration
integer(c_int) :: j
@end smallexample
Note that pointer arguments also frequently need the @code{VALUE} attribute.
Note that pointer arguments also frequently need the @code{VALUE} attribute,
see @ref{Working with Pointers}.
Strings are handled quite differently in C and Fortran. In C a string
is a @code{NUL}-terminated array of characters while in Fortran each string
@ -2096,7 +2098,7 @@ literal has the right type; typically the default character
kind and @code{c_char} are the same and thus @code{"Hello World"}
is equivalent. However, the standard does not guarantee this.
The use of pointers is now illustrated using the C library
The use of strings is now further illustrated using the C library
function @code{strncpy}, whose prototype is
@smallexample
@ -2128,8 +2130,13 @@ example, we ignore the return value:
end
@end smallexample
C pointers are represented in Fortran via the special derived type
@code{type(c_ptr)}, with private components. Thus one needs to
The intrinsic procedures are described in @ref{Intrinsic Procedures}.
@node Working with Pointers
@subsection Working with Pointers
C pointers are represented in Fortran via the special opaque derived type
@code{type(c_ptr)} (with private components). Thus one needs to
use intrinsic conversion procedures to convert from or to C pointers.
For example,
@ -2147,14 +2154,131 @@ For example,
@end smallexample
When converting C to Fortran arrays, the one-dimensional @code{SHAPE} argument
has to be passed. Note: A pointer argument @code{void *} matches
@code{TYPE(C_PTR), VALUE} while @code{TYPE(C_PTR)} matches @code{void **}.
has to be passed.
If a pointer is a dummy-argument of an interoperable procedure, it usually
has to be declared using the @code{VALUE} attribute. @code{void*}
matches @code{TYPE(C_PTR), VALUE}, while @code{TYPE(C_PTR)} alone
matches @code{void**}.
Procedure pointers are handled analogously to pointers; the C type is
@code{TYPE(C_FUNPTR)} and the intrinsic conversion procedures are
@code{C_F_PROC_POINTER} and @code{C_FUNLOC}.
@code{C_F_PROCPOINTER} and @code{C_FUNLOC}.
The intrinsic procedures are described in @ref{Intrinsic Procedures}.
Let's consider two examples of actually passing a procedure pointer from
C to Fortran and vice versa. Note that these examples are also very
similar to passing ordinary pointers between both languages.
First, consider this code in C:
@smallexample
/* Procedure implemented in Fortran. */
void get_values (void (*)(double));
/* Call-back routine we want called from Fortran. */
void
print_it (double x)
@{
printf ("Number is %f.\n", x);
@}
/* Call Fortran routine and pass call-back to it. */
void
foobar ()
@{
get_values (&print_it);
@}
@end smallexample
A matching implementation for @code{get_values} in Fortran, that correctly
receives the procedure pointer from C and is able to call it, is given
in the following @code{MODULE}:
@smallexample
MODULE m
IMPLICIT NONE
! Define interface of call-back routine.
ABSTRACT INTERFACE
SUBROUTINE callback (x)
USE, INTRINSIC :: ISO_C_BINDING
REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x
END SUBROUTINE callback
END INTERFACE
CONTAINS
! Define C-bound procedure.
SUBROUTINE get_values (cproc) BIND(C)
USE, INTRINSIC :: ISO_C_BINDING
TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc
PROCEDURE(callback), POINTER :: proc
! Convert C to Fortran procedure pointer.
CALL C_F_PROCPOINTER (cproc, proc)
! Call it.
CALL proc (1.0_C_DOUBLE)
CALL proc (-42.0_C_DOUBLE)
CALL proc (18.12_C_DOUBLE)
END SUBROUTINE get_values
END MODULE m
@end smallexample
Next, we want to call a C routine that expects a procedure pointer argument
and pass it a Fortran procedure (which clearly must be interoperable!).
Again, the C function may be:
@smallexample
int
call_it (int (*func)(int), int arg)
@{
return func (arg);
@}
@end smallexample
It can be used as in the following Fortran code:
@smallexample
MODULE m
USE, INTRINSIC :: ISO_C_BINDING
IMPLICIT NONE
! Define interface of C function.
INTERFACE
INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C)
USE, INTRINSIC :: ISO_C_BINDING
TYPE(C_FUNPTR), INTENT(IN), VALUE :: func
INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
END FUNCTION call_it
END INTERFACE
CONTAINS
! Define procedure passed to C function.
! It must be interoperable!
INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C)
INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
double_it = arg + arg
END FUNCTION double_it
! Call C function.
SUBROUTINE foobar ()
TYPE(C_FUNPTR) :: cproc
INTEGER(KIND=C_INT) :: i
! Get C procedure pointer.
cproc = C_FUNLOC (double_it)
! Use it.
DO i = 1_C_INT, 10_C_INT
PRINT *, call_it (cproc, i)
END DO
END SUBROUTINE foobar
END MODULE m
@end smallexample
@node Further Interoperability of Fortran with C
@subsection Further Interoperability of Fortran with C