Pass and return structs (by copy) between C and Python using CFFI

cffi-python-struct.py

from cffi import FFI
ffi = FFI()

ffi.cdef("""
typedef struct T T;
struct T
{
  int a;
  float b;
};

void pass_a_struct(T somedata);
T get_a_struct();

"""
)
# Compile the C sources to produce the following .dll (or .so under *nix) 
lib = ffi.dlopen("somelib.dll")

# Create a new C struct of type T
fooStruct = ffi.new("struct T *")

# Using struct fields defined in C code is as simple as this
fooStruct.a = 12;
fooStruct.b = 3.5;

# To pass the struct you need to dereference it (like you would in C)
lib.pass_a_struct(fooStruct[0])

# To get the struct use simple assignement
fooStruct = lib.get_a_struct()

# And that's it
print("Got : ",fooStruct)
print("T.a",fooStruct.a)
print("T.b",fooStruct.b)

somelib.c

#include "somelib.h"

static T myStruct;

void pass_a_struct(T somedata)
{
  myStruct.a = somedata.a * 2;
  myStruct.b = somedata.b / 3.f;
}


T get_a_struct()
{
  return myStruct;
}

somelib.h

#ifndef SOMELIB_H_
#define SOMELIB_H_

typedef struct T T;
struct T
{
  int a;
  float b;
};

// pass a struct
void pass_a_struct(T somedata);

// get back a struct
T get_a_struct();

#endif