very simple shared dll with ctypes

[mclaugb]

I have created a simple windows small_dll.dll exporting a function that does
a computation using C and C++ classes which i wish to call from Python. I
have read lots of ctypes documentation but I still dont quite understand how
to call the function.

As a test, I have written a much simpler mathematical function below to try
to get it to work from Python.

I am trying to call this from python by:

>>from ctypes import *

>>print cdll.small_dll. adder(c_double( 5.343534),c_dou ble(3.4432))

>>2223968

Can someone give me a few tips to get going!
The DLL declaration is below.



#include<window s.h>

#if defined(_MSC_VE R)

#define DLL extern "C" __declspec(dlle xport)

#else

#define DLL

#endif


DLL double adder(double a, double b){

double c;

c=a+b;

return c;

}

[Thomas Heller]

Re: very simple shared dll with ctypes

mclaugb schrieb:

I have created a simple windows small_dll.dll exporting a function that does
a computation using C and C++ classes which i wish to call from Python. I
have read lots of ctypes documentation but I still dont quite understand how
to call the function.
>
As a test, I have written a much simpler mathematical function below to try
to get it to work from Python.
>
I am trying to call this from python by:
>

>>>from ctypes import *
>>>print cdll.small_dll. adder(c_double( 5.343534),c_dou ble(3.4432))
>>>2223968

>
Can someone give me a few tips to get going!

You should assign the .restype and the .argtypes attributes to your function.
That gives the the proper result, and you don't have to pack the arguments into
c_double yourself.

The DLL declaration is below.
>
#include<window s.h>
#if defined(_MSC_VE R)
#define DLL extern "C" __declspec(dlle xport)
#else
#define DLL
#endif
>
DLL double adder(double a, double b){
double c;
c=a+b;
return c;
}
>

from ctypes import *
adder = cdll.small_dll. adder
adder.restype = c_double
adder.argtypes = c_double, c_double

print adder(5.343534, 3.4432)


Thomas

[mclaugb]

Re: very simple shared dll with ctypes

Assigining restype and argtypes works!

"Thomas Heller" <theller@ctypes .orgwrote in message
news:mailman.92 28.1182256599.3 2031.python-list@python.org ...

mclaugb schrieb:

>I have created a simple windows small_dll.dll exporting a function that
>does
>a computation using C and C++ classes which i wish to call from Python.
>I
>have read lots of ctypes documentation but I still dont quite understand
>how
>to call the function.
>>
>As a test, I have written a much simpler mathematical function below to
>try
>to get it to work from Python.
>>
>I am trying to call this from python by:
>>

>>>>from ctypes import *
>>>>print cdll.small_dll. adder(c_double( 5.343534),c_dou ble(3.4432))
>>>>2223968

>>
>Can someone give me a few tips to get going!

>
You should assign the .restype and the .argtypes attributes to your
function.
That gives the the proper result, and you don't have to pack the arguments
into
c_double yourself.
>

>The DLL declaration is below.
>>
>#include<windo ws.h>
>#if defined(_MSC_VE R)
>#define DLL extern "C" __declspec(dlle xport)
>#else
>#define DLL
>#endif
>>
>DLL double adder(double a, double b){
>double c;
>c=a+b;
>return c;
>}
>>

>
from ctypes import *
adder = cdll.small_dll. adder
adder.restype = c_double
adder.argtypes = c_double, c_double
>
print adder(5.343534, 3.4432)
>
>
Thomas
>