interfacing python3 with C, ctypes

/*
 articles:

 Interfacing Python with C using ctypes
 http://blog.prashanthellina.com/interfacing-python-with-c-using-ctypes.html

 Shared objects for the object disoriented!
 https://www.ibm.com/developerworks/library/l-shobj/

 ctypes — A foreign function library for Python
 https://docs.python.org/3/library/ctypes.html

 Interfacing Python and C using Ctypes
 http://indico.ictp.it/event/7657/session/4/contribution/19/material/1/0.pdf

 */

/*

build shared library:

gcc -fPIC -c test.c
ld -shared -soname libtest.so.1 -o libtest.so.1.0 -lc test.o

file testc.py

# begin

from ctypes import *

lib = cdll.LoadLibrary('./libtest.so.1.0')

print(lib.addi(1, 2))

a = c_float(1.7)
b = c_float(1.8)

print("a: %.5f b: %.5f" % (a.value,b.value))

lib.addf.restype=c_float
print("%.5f" % lib.addf(c_float(1.7),c_float(1.8)))


print("a before (1): %.5f" % a.value)
lib.addfbr(byref(a))
print("a after (1): %.5f" % a.value)


f_array = (c_float * 16)(*range(16))

print(sizeof(f_array))

f_array[0] = 300.1
f_array[1] = 300.2

lib.addfbrarr.restype=c_bool

retval = c_bool()

print("before (2): %.5f %.5f" % (f_array[0],f_array[1]))
retval = lib.addfbrarr(byref(f_array),16)
if retval:
    print("ERROR: addfbrarr")
else:
    print("after (2): %.5f %.5f" % (f_array[0],f_array[1]))

# end

run:

python3 testc.py

 */

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

void _init()
{
    printf("init\n");
}

void _fini()
{
    printf("fini\n");
}

int addi(int a, int b)
{

    return a + b;
}

float addf(float a, float b)
{

    return a + b;
}

void addfbr(float* a)
{
    *a = *a + 1.0f;
}


bool addfbrarr(float* a, unsigned int numOfE)
{

    printf("sizeof float %zu\n",sizeof(float));
    printf("sizeof float* %zu\n",sizeof(float*));

    float* tmp;
    unsigned int offset = 0;

    if(offset<numOfE)
    {
    tmp = a + offset;
    printf("address of tmp: %p\n", (void*) tmp);
    *tmp = *tmp + 1.0f;
    }
    else return 1;

    offset++;

    //tmp += 1; adds sizeof(float)

    if(offset<numOfE)
    {
    tmp = a + offset;
    printf("address of tmp: %p\n", (void*) tmp);
    *tmp = *tmp + 1.0f;
    }
    else return 1;

    return 0;
}

/*

output:

init
3
a: 1.70000 b: 1.80000
3.50000
a before (1): 1.70000
a after (1): 2.70000
64
before (2): 300.10001 300.20001
sizeof float 4
sizeof float* 8
address of tmp: 0x7f93fa8fc6f0
address of tmp: 0x7f93fa8fc6f4
after (2): 301.10001 301.20001
fini

*/