SWIG Python - wrapping a function that expects a double pointer to a structure

Question

I am wrapping a C library that contains a structure:

struct SCIP { //... } 

and a function that creates such a structure:

 void SCIPcreate(SCIP** s) 

SWIG generates a python SCIP class and a SCIPcreate(*args) function SCIPcreate(*args) .

When I now try to call SCIPcreate() in python, it explicitly expects a parameter of type SCIP** , how should I create such a thing?

Or should you try and extend the SCIP class with a constructor that calls SCIPcreate() automatically? If so, how can I do this?

Answer 1

Given the header file:

 struct SCIP {}; void SCIPcreate(struct SCIP **s) { *s = malloc(sizeof **s); } 

We can wrap this function using:

 %module test %{ #include "test.h" %} %typemap(in,numinputs=0) struct SCIP **s (struct SCIP *temp) { $1 = &temp; } %typemap(argout) struct SCIP **s { %set_output(SWIG_NewPointerObj(SWIG_as_voidptr(*$1), $*1_descriptor, SWIG_POINTER_OWN)); } %include "test.h" 

which consists of two typical forms: one to create a local temporary pointer that will be used as input for the function, and the other to copy the value of the pointer after the call to return.

Alternatively, you can also use %inline to set the overload:

 %newobject SCIPcreate; %inline %{ struct SCIP *SCIPcreate() { struct SICP *temp; SCIPcreate(&temp); return temp; } %}