Intel® Fortran Compiler 18.0 Developer Guide and Reference
A Fortran procedure is interoperable if it has the BIND attribute.
A Fortran procedure interface is interoperable with a C function prototype if the following is true:
The interface has the BIND attribute
One of the following is true:
The interface describes a function whose result variable is a scalar that is interoperable with the result of the prototype.
The interface describes a subroutine and the prototype has a result type of void.
The number of dummy arguments of the interface is equal to the number of formal parameters of the prototype.
Any dummy argument with the VALUE attribute is interoperable with the corresponding formal parameter of the prototype.
Any dummy argument without the VALUE attribute corresponds to a formal parameter of the prototype that is of a pointer type, and one of the following is true:
The dummy argument is interoperable with an entity of the referenced type of the formal parameter.
The dummy argument is a nonallocatable nonpointer variable of type CHARACTER with assumed character length and the formal parameter is a pointer to the C descriptior descriptor CFI_cdesc_t.
The dummy argument is allocatable, assumed-shape, assumed-rank, or a pointer without the CONTIGUOUS attribute, and the formal parameter is a pointer to the C descriptior descriptor CFI_cdesc_t.
The dummy argument is assumed-type and not allocatable, assumed-shape, assumed-rank, or a pointer, and the formal parameter is a pointer to void.
Each allocatable or pointer dummy argument of type CHARACTER has deferred character length.
The prototype does not have variable arguments as denoted by an ellipsis (...).
In an invocation of an interoperable procedure whose Fortran interface has an assumed-shape or assumed-rank dummy argument with the CONTIGUOUS attribute, the associated effective argument can be an array that is not contiguous or it can be the address of a C descriptor for such an array.
If the procedure is invoked from Fortran or the procedure is a Fortran procedure, the Fortran processor will handle the difference in contiguity.
If the procedure is invoked from C or the procedure is a C procedure, the C code within the procedure must be able to handle the situation of receiving a discontiguous argument.
An actual argument that is absent in a reference to an interoperable procedure is indicated by a corresponding formal parameter with the value of a null pointer. An optional dummy argument that is absent in a reference to an interoperable procedure from a C function is indicated by a corresponding argument with the value of a null pointer.
The following rules also apply:
C functions must not invoke a function pointer whose value is the result of a reference to C_FUNLOC with a noninteroperable argument.
When passing an argument to a C procedure where the corresponding C formal parameter is a C descriptor, Fortran must pass a C descriptor and, on return, ensure that any updates to the C descriptor are reflected in Fortran.
If the interface specifies that the dummy argument is CONTIGUOUS, the passed argument (and the C descriptor’s description of that argument, if relevant) must be contiguous.
A Fortran procedure with BIND(C) that has a dummy argument that is assumed-length CHARACTER or is allocatable, assumed-shape, assumed-rank, or a pointer without CONTIGUOUS must accept that argument as a C descriptor and make sure that on return, the C descriptor reflects any changes made to the argument during execution of the Fortran procedure.
A Fortran procedure with one of the following arguments must accept that argument as a C descriptor and make sure that on return, the C descriptor reflects any changes made to the argument during execution of the Fortran procedure:
A dummy argument that is assumed-length CHARACTER
A dummy argument that is allocatable, assumed-shape, assumed-rank, or a pointer without CONTIGUOUS