fficall.c

#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

void (*f)(void);

void fatal(const char * info) {
    printf("error: %s", info);
    exit(1);
}

int main(int argc, char** argv) {
    void* lib = dlopen("libmymodule.so", RTLD_LAZY);
    if (lib == NULL)
        fatal(dlerror());

    f = (void (*)(void)) dlsym(lib, "get_point_distance");

    printf("address: %p", f);
    return 0;
}

luajit-cstruct.lua

ffi = require('ffi')
ffi.cdef[[
typedef struct point point_t;
struct point {
  double x;
  double y;
};
]]
local points = ffi.new("point_t[?]", n)
points[1].x = 1.0
points[2].y = 3.0

luajit-helloworld.lua

local ffi = require("ffi")
ffi.cdef[[
int printf(const char *fmt, ...);
]]
ffi.C.printf("Hello %s!", "world")

Makefile

step0:
	gcc -shared -o libmymodule.so -fPIC mymodule.c

mymodule.c

#include <math.h>
#include "mymodule.h"

double get_point_distance(const point_t* p1, const point_t* p2) {
    return sqrt((p2->x - p1->x) * (p2->x - p1->x) + (p2->y - p1->x) * (p2->y - p1->x));
}

mymodule.h

#ifndef MYMODULE_H
#define MYMODULE_H

typedef struct point point_t;

struct point {
  double x;
  double y;
};

double get_point_distance(const point_t* p1, const point_t* p2);

#endif

python-cstruct.py

ffi = FFI()
ffi.cdef("""
typedef struct point point_t;
struct point {
  double x;
  double y;
};
""")
points = ffi.new("point_t[]", 2)
points[0].x = 1.0
points[1].y = 3.0

python-helloworld.py

from cffi import FFI
ffi = FFI()
ffi.cdef("""
    int printf(const char *format, ...);   // copy-pasted from the man page
""")
C = ffi.dlopen(None)                     # loads the entire C namespace
arg = ffi.new("char[]", "world")         # equivalent to C code: char arg[] = "world";
C.printf("hi there, %s.\n", arg)         # call printf