Typemaps¶

Typemaps are used to add code to the generated wrappers to replace the default code.

The typemaps work together to pass variables and metadata between Fortran and C.

Fortran¶

A Fortran wrapper is created out of several segments.

{F_subprogram} {F_name_impl}({F_arguments}){F_result_clause}
  arg_f_use
  arg_f_decl
  ! splicer begin
  declare
  pre_call
  call
  post_call
  ! splicer end
end {F_subprogram} {F_name_impl}

buf_arg¶

arg

default.

shadow size capsule context len_trim len

c_local_var¶

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).

call¶

Code used to call the function. Defaults to {F_result} = {F_C_call}({F_arg_c_call})

declare¶

A list of declarations needed by pre_call or post_call. Usually a c_local_var is sufficient.

f_helper¶

Blank delimited list of helper function names to add to generated Fortran code. These functions are defined in whelper.py. There is no current way to add additional functions.

f_module¶

USE statements to add to Fortran wrapper. A dictionary of list of ONLY names:

f_module:
  iso_c_binding:
  - C_SIZE_T

post_call¶

Statement to execute after call. Can be use to cleanup after pre_call or to coerce the return value.

pre_call¶

Statement to execute before call, often to coerce types when f_cast cannot be used.

need_wrapper¶

If true, the Fortran wrapper will always be created. This is used when an assignment is needed to do a type coercion; for example, with logical types.

C¶

The C_code field has a default value of:

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

buf_args¶

buf_args lists the arguments which are used by the wrapper. The default is to provide a one-for-one correspondance with the arguments of the function which is being wrapped. However, often an additional function is created which will pass additional or different arguments to provide meta-data about the argument.

The Fortran wrapper will call the generated ‘bufferified’ function and provide the meta-data to the C wrapper.

arg

Use the library argument as the wrapper argument. This is the default when buf_args is not explicit.

capsule

An argument of type C_capsule_data_type/F_capsule_data_type. It provides a pointer to the C++ memory as well as information to release the memory.

context

An argument of C_context_type/F_context_type. For example, used with std::vector to hold address and size of data contained in the argument in a form which may be used directly by Fortran.

c_var_context

len

Result of Fortran intrinsic LEN for string arguments. Type int.

len_trim

Result of Fortran intrinsic LEN_TRIM for string arguments. Type int.

size

Result of Fortran intrinsic SIZE for array arguments. Type long.

shadow

Argument will be of type C_capsule_data_type.

c_header¶

List of blank delimited header files which will be included by the generated header for the C wrapper. These headers must be C only. For example, size_t requires stddef.h:

type: size_t
fields:
    c_type: size_t
    cxx_type: size_t
    c_header: <stddef.h>

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.

The local variable can be passed in when buf_args is shadow.

call¶

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

cxx_header¶

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

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 in turns will 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.

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;

destructor_name¶

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

destructor_name: std_vector_{cxx_T}

final¶

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

pre_call¶

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

post_call¶

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

ret¶

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

return_type¶

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

return_cptr¶

If true, the function will return a C pointer. This will be used by the Fortran interface to declare the function as type(C_PTR).

How typemaps are found¶

alias¶

Names another node which will be used for its contents.