ctypes.py

from ctypes import *
lib = CDLL("./libupdateptr.so")

i = c_int()
print(lib.update_int(byref(i)))
print(i.value)

print(lib.update_int2(byref(i)))
print(i.value)

j = c_long()
print(lib.update_long(byref(j)))
print(j.value)

k = c_ulong()
print(lib.update_ulong(byref(k)))
print(k.value)

l = c_longlong()
print(lib.update_long_long(byref(l)))
print(l.value)

m = c_double()
print(lib.update_double(byref(m)))
print(m.value)

fiddle.rb

require 'fiddle/import'
                          
module UpdatePtr                           
  extend Fiddle::Importer
  dlload "./libupdateptr.so"                   
                          
  extern "int update_int(*int)"
  extern "int update_int2(*int)"
  extern "int update_long(*long)"              
  extern "int update_ulong(*unsigned long)"
  extern "int update_long_long(*long long)"
  extern "int update_double(*double)"
end

i = Fiddle::Pointer.malloc(Fiddle::SIZEOF_INT)
p UpdatePtr.update_int(i)
p [i[0, i.size], i[0, i.size].unpack("i!")]

p UpdatePtr.update_int2(i)
p [i[0, i.size], i[0, i.size].unpack("i!")]

j = Fiddle::Pointer.malloc(Fiddle::SIZEOF_LONG)
p UpdatePtr.update_long(j)
p j[0, j.size].unpack("l!")

k = Fiddle::Pointer.malloc(Fiddle::SIZEOF_LONG)
p UpdatePtr.update_ulong(k)
p k[0, k.size].unpack("L!")

l = Fiddle::Pointer.malloc(Fiddle::SIZEOF_LONG * 2)
p UpdatePtr.update_long_long(l)
p l[0, l.size].unpack("q!")

m = Fiddle::Pointer.malloc(Fiddle::SIZEOF_DOUBLE)
p UpdatePtr.update_double(m)
p m[0, m.size].unpack("d")

Makefile

default: libupdateptr.so updateptr.o

updateptr.o: updateptr.c
	gcc -fPIC -c ./updateptr.c -o updateptr.o
libupdateptr.so: updateptr.o
	gcc -shared updateptr.o -o libupdateptr.so

updateprt.c

#define INT_VALUE 5         
#define INT_VALUE2 1234567
#define LONG_VALUE 68719486735L
#define ULONG_VALUE 1125899906852623UL
#define LONG_LONG_VALUE 1125899906852624LL
#define DOUBLE_VALUE 3.14159265       
                     
int update_int(int* ptr) {
  *ptr = INT_VALUE;
  return 0;
}                                     

int update_int2(int* ptr) {
  *ptr = INT_VALUE2;
  return 0;
}

int update_long(long* ptr) {
  *ptr = LONG_VALUE;
  return 0;
}

int update_ulong(unsigned long* ptr) {
  *ptr = ULONG_VALUE;
  return 0;
}

int update_long_long(long long* ptr) {
  *ptr = LONG_LONG_VALUE;
  return 0;
}

int update_double(double* ptr) {
  *ptr = DOUBLE_VALUE;
  return 0;
}