C Statements¶

Note

Work in progress

extern "C" {

{C_return_type} {C_name}({C_prototype})
{
    {pre_call}
    {call_code}   {call}    arg_call
    {post_call_pattern}
    {post_call}
    {final}
    {ret}
}

C_prototype -> c_arg_decl

A corresponding bind(C) interface can be created for Fortran.

{F_C_subprogram} {F_C_name}({F_C_arguments}) &
    {F_C_result_clause} &
    bind(C, name="{C_name}")
    f_module / f_module_line
    f_import
    arg_c_decl
end {F_C_subprogram} {F_C_name}

Where F_C_clause = F_C_arguments = f_c_arg_names arg_c_decl = f_arg_decl, f_result_decl F_C_result_clause = f_result_var

Lookup statements¶

The statements for an argument are looked up by converting the type and attributes into an underscore delimited string.

language - c
intent - in, out, inout, function, ctor, dtor, getter, setter
group from typemap. native
pointer - scalar, *, **
api - from attribute buf, capsule, capptr, cdesc and cfi.
deref - from attribute allocatable, pointer, raw, result-as-arg, scalar

template¶

Each template argument is appended to the initial statement name. targ, group and pointer

c_statements¶

name¶

A name can contain variants separated by /.

- name: c_in/out/inout_native_*_cfi

This is equivelent to having three groups:

- name: c_in_native_*_cfi
- name: c_out_native_*_cfi
- name: c_inout_native_*_cfi

iface_header¶

List of header files which will be included in the generated header for the C wrapper. These headers must be C only and will be included after ifdef __cplusplus. Used for headers needed for declarations in c_arg_decl. Can contain headers required for the generated prototypes.

For example, ISO_Fortran_binding.h is C only.

impl_header¶

A list of header files which will be added to the C wrapper implementation. These headers may include C++ code.

c_helper¶

A blank delimited list of helper functions which will be added to the wrapper file. The list will be formatted to allow for additional flexibility:

c_helper: capsule_data_helper vector_context vector_copy_{cxx_T}

These functions are defined in whelper.py. There is no current way to add additional functions.

c_local_var¶

If a local C variable is created for the return value by post_call, c_local_var indicates if the local variable is a pointer or scalar. For example, when a structure is returned by a C++ function, the C wrapper creates a local variable which contains a pointer to the C type of the struct.

If true, generate a local variable using the C declaration for the argument. This variable can be used by the pre_call and post_call statements. A single declaration will be added even if with intent(inout).

cxx_local_var¶

If a local C++ variable is created for an argument by pre_call, cxx_local_var indicates if the local variable is a pointer or scalar. .. This sets cxx_var is set to SH_{c_var}. This will properly dereference the variable when passed to the C++ function. It will also set the format fields cxx_member. For example, a std::string argument is created for the C++ function from the char * argument passed into the C API wrapper.

       name="c_inout_string",
       cxx_local_var="scalar",
       pre_call=["{c_const}std::string {cxx_var}({c_var});"],

Set to **return** when the *c_var* is passed in as an argument and
a C++ variable must be created.
Ex ``c_function_shadow``.
In this case, *cxx_to_c* is defined so a local variable will already
be created, unless *language=c* in which case *cxx_to_c* is unneeded.

c_arg_decl¶

A list of declarations to append to the prototype in the C wrapper. Defaults to None which will cause Shroud to generate an argument from the wrapped function’s argument. Functions do not add arguments by default.

f_arg_decl¶

A list of dummy argument declarations in the Fortran bind(C) interface. Used when buf_arg includes “arg_decl”. The variable to be declared is c_var. f_module can be used to add USE statements needed by the declarations.

f_c_arg_names¶

Names of arguments to pass to C function. Used when buf_arg is arg_decl. Defaults to {F_C_var}.

Note

c_arg_decl, f_arg_decl, and f_c_arg_names must all exist in a group and have the same number of names.

f_result_decl¶

A list of declarations in the Fortran interface for a function result value.

f_import¶

List of names to import into the Fortran interface. The names will be expanded before being used.

In this example, Shroud creates F_array_type derived type in the module and it is used in the interface.

f_import=["{F_array_type}"],

f_module¶

Fortran modules used in the Fortran interface:

f_module=dict(iso_c_binding=["C_PTR"]),

f_module_line¶

Fortran modules used in the Fortran interface as a single line which allows format strings to be used.

f_module_line="iso_c_binding:{f_kind}",

The format is:

module ":" symbol [ "," symbol ]* [ ";" module ":" symbol [ "," symbol ]* ]

arg_call¶

pre_call¶

Code used with intent(in) arguments to convert from C to C++.

call¶

Code to call function. This is usually generated. An exception which require explicit call code are constructors and destructors for shadow types.

post_call¶

Code used with intent(out) arguments and function results. Can be used to convert results from C++ to C.

final¶

Inserted after post_call and before ret. Can be used to release intermediate memory in the C wrapper.

ret¶

Code for return statement. Usually generated but can be replaced. For example, with constructors.

Useful to convert a subroutine into a function. For example, convert a void function which fills a std::vector to return the number of items.

return_type¶

Explicit return type when it is different than the functions return type. For example, with shadow types.

return_type: long
ret:
- return Darg->size;

return_type can also be used to convert a C wrapper into a void function. This is useful for functions which return pointers but the pointer value is assigned to a subroutine argument which holds the pointer (For example, CFI_cdesc_t). The type(C_PTR) which would be return by the C wrapper is unneeded by the Fortran wrapper.

destructor_name¶

A name for the destructor code in destructor. Must be unique. May include format strings:

destructor_name: std_vector_{cxx_T}

destructor¶

A list of lines of code used to delete memory. Usually allocated by a pre_call statement. The code is inserted into C_memory_dtor_function which will provide the address of the memory to destroy in the variable void *ptr. For example:

destructor:
-  std::vector<{cxx_T}> *cxx_ptr = reinterpret_cast<std::vector<{cxx_T}> *>(ptr);
-  delete cxx_ptr;

owner¶

Set owner of the memory. Similar to attribute owner.

Used where the new` operator is part of the generated code. For example where a class is returned by value or a constructor. The C wrapper must explicitly allocate a class instance which will hold the value from the C++ library function. The Fortran shadow class must keep this copy until the shadow class is deleted.

Defaults to library.

temps¶

A list of suffixes for temporary variable names.

   temps=["len"]

Create variable names in the format dictionary using
``{fmt.c_temp}{rootname}_{name}``.
For example, argument *foo* creates *SHT_foo_len*.

local¶

Similar to temps but uses {fmt.C_local}{rootname}_{name}. temps is intended for arguments and is typically used in a mixin group. local is used by group to generate names for local variables. This allows creating names without conflicting with temps from a mixin group.