CODEWITHSUNDEEP
pythonctypes
Dev.K.
Dev.K.

Reputation: 2488

Python Ctypes Double De-reference Pointer

I have a C function in a DLL which looks like this.

ProcessAndsend(Format *out,      // IN
            char const *reqp,    // IN
            size_t reqLen,       // IN
            Bool *Status,        // OUT
            char const **reply,  // OUT
            size_t *resLen)      // OUT

When the call is successful something get saved to all the OUT parameters.

Using python ctypes (On Windows) I want to double de-reference the **reply pointer and see what is the value there.

Thanks in Adv.

Upvotes: 1

Views: 1236

Answers (1)

Mark Tolonen
Mark Tolonen

Reputation: 177600

I don't have your Format and Bool types, so with some substitutions, here's some sample DLL code:

#include <stddef.h>
__declspec(dllexport) void ProcessAndsend(char *out,        // IN
                                          char const *reqp,   // IN
                                          size_t reqLen,      // IN
                                          int *Status,       // OUT
                                          char const **reply, // OUT
                                          size_t *resLen)     // OUT
{
    *Status = 1;
    *reply = "test";
    *resLen = 5;
}

This will retrieve the output data. Just create some instances of the correct ctypes types and pass them by reference:

>>> from ctypes import *
>>> dll = CDLL('your.dll')
>>> f = dll.ProcessAndsend
>>> f.argtypes = c_char_p,c_char_p,c_size_t,POINTER(c_int),POINTER(c_char_p),POINTER(c_size_t)
>>> f.restype = None
>>> status = c_int()
>>> reply = c_char_p()
>>> size = c_size_t()
>>> f('abc','def',3,byref(status),byref(reply),byref(size))
>>> status
c_long(1)
>>> reply
c_char_p('test')
>>> size
c_ulong(5L)

Upvotes: 3

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