[Python] ctypes

Dll funkcija spisana v C

function GetValue(RecNr: Integer; out Value: PAnsiChar): Integer;

V "out Value" naj bi se vpisala vrednost (tudi iz 0x00 znakov), se pravi mora bit Value nek pointer.

Poizkusil sem malo morje kombinacij, pa sem dobival neke "pointerje" ali pa errorje...

Eden od mojih Python poizkusov

def GetPozicijaFromHistory1(RecNr):
    obj = self.dll.GetValue
    obj.argtypes = [c_int, POINTER(c_char_p)]
    obj.restype = c_long
    field_value = c_char_p()
    obj(RecNr, byref(field_value)))

in rezultat

<cparam 'P' (0x01A7CE18)>

Vprašanje... kako dobim vrednost?

@twom: Vaša deklaracija funkcije GetValue ne ustreza C sintaksi. Primer za Pascal DLL lib, C++ DLL lib in Python ctypes.
Bonus: V C++ se poljubno spremeni vrednost po referenci , ki jo deklarirate v Pythonu.
Feature: V Pascalu se ne spremeni deklarirana vrednostv Pythonu.

// FreePascal

library PascalDllLib;
 
{$mode objfpc}{$H+}
 
function GetValue(RecNr: Integer; out Value : PAnsiChar): Integer; stdcall;
begin
  writeln('Pascal RecNr: ', RecNr);
  Value:= PAnsiChar('thisisalongtext');
  writeln('Pascal Value: ', Value);
  Result:= Length(Value);
  writeln('Pascal Result: ', Result);
end;
 
exports
  GetValue;
 
begin
end.
 

// Python

from ctypes import CDLL, POINTER, addressof, byref, c_char_p, c_int, c_long, create_string_buffer
 
class CDLLExample:
 
    def __init__(self) -> None:
        self.dll = CDLL("X:\\PascalDllLib.dll") # DLL file (absolute path)
 
    def GetPozicijaFromHistory1(self, RecNr) -> int:
        obj = self.dll.GetValue
        obj.argtypes = [c_int, POINTER(c_char_p)]
        obj.restype = c_long
        str_buffer = create_string_buffer(b'slotech', 256)
        field_value = c_char_p(addressof(str_buffer))
        return_value = obj(RecNr, byref(field_value)) # call Pascal function GetValue
        print('Pascal str buffer value: %s' % str_buffer.value) # get Value
        return return_value
 
if __name__ == '__main__':
    print("Python main")
    m = CDLLExample()
    return_value = m.GetPozicijaFromHistory1(1)
    print('Python return value: %s' % value)
 

// Visual C++

// dllmain.cpp : Defines the entry point for the DLL application.
#include "pch.h"
#include <stdio.h>
 
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}
 
#ifdef __cplusplus
extern "C" {
#endif
 
__declspec(dllexport) int GetValue(INT recNr, CHAR** value)
{
    printf("C++ recNr: %d\n", recNr);
    strcpy_s(*value, 5, "C++!\0");
    printf("C++ value: %s\n", *value);
    return strlen(*value);
}
 
#ifdef __cplusplus
}
#endif