Python calling an SDK function in DLL of a sensor that takes poi

ghz 11hours ago ⋅ 7 views

Python calling an SDK function in DLL of a sensor that takes pointer IP and port and return a void* (void* a handle to the profile sensor.)

I am just new in Python. I am trying to connect to a laser sensor through its DLL library. The SDK functions in this Library are compiled in C++ language.

By using ctypes in python my first try is to call the EthernetScanner_Connect function. The function parameters are as follow:

void* EthernetScanner_Connect(char *chIP, char *chPort, int iTimeOut)

According to the function discription in c++ it should return NULL pointer if a failure in connection occurs, otherwise it should return the handle to the profile sensor, which is gonna be used in other functions.

My code on python untill now:

from ctypes import *

lib=windll.LoadLibrary("c:\\EthernetScanner.dll")

if lib:
    print("the Library is loaded")

EthernetScanner_Connect = getattr(lib,"EthernetScanner_Connect")

EthernetScanner_Connect.restype = c_void_p
EthernetScanner_Connect.argtypes =[c_char_p,c_char_p,c_int]
x = EthernetScanner_Connect(b"193.164.200.1\0",b"32407\0",0)

print(x)

while I am expecting NULL from this function because i am not connected to the sensor yet, it is giving me the following:

the Library is loaded
45940800

Answer

It seems you're on the right track using ctypes to load the DLL and call the EthernetScanner_Connect function. The issue you're facing — where the function returns an unexpected pointer value (e.g., 45940800) instead of NULL — can happen for a few reasons. Let's go through the code and troubleshoot step by step.

1. Ensure Proper Argument Types

The arguments to the EthernetScanner_Connect function are as follows:

void* EthernetScanner_Connect(char *chIP, char *chPort, int iTimeOut)

You are already using c_char_p for the chIP and chPort arguments and c_int for iTimeOut, which is correct. However, the null-termination (\0) you're using in b"193.164.200.1\0" and b"32407\0" is not strictly necessary when using ctypes.c_char_p for string arguments. c_char_p automatically handles null-termination of byte strings. So you can remove the \0 characters from the byte strings.

2. Check the Return Type

You're correctly setting restype = c_void_p, since the function returns a pointer (i.e., void*). If the connection fails, the function should return NULL (which in C/C++ is equivalent to None in Python, or 0 when interpreted as a pointer).

3. Handle the Return Value

If the function returns a non-NULL value, you should expect it to be a pointer, which you can treat as an integer. A NULL pointer is typically represented by 0 or None in Python.

Updated Code

Here’s how you can modify your code to correctly handle the connection and interpret the return value:

from ctypes import *

# Load the library
lib = windll.LoadLibrary("c:\\EthernetScanner.dll")

if lib:
    print("The Library is loaded")

# Get the function from the library
EthernetScanner_Connect = getattr(lib, "EthernetScanner_Connect")

# Set the argument and return types
EthernetScanner_Connect.restype = c_void_p
EthernetScanner_Connect.argtypes = [c_char_p, c_char_p, c_int]

# Call the function with appropriate arguments
x = EthernetScanner_Connect(b"193.164.200.1", b"32407", 0)

# Print the returned pointer (handle)
print(f"Returned Pointer: {x}")

# Check if the connection was successful or failed
if x == 0:
    print("Connection failed (NULL pointer returned)")
else:
    print("Connection successful, handle:", x)

Key Points:

  1. Remove the Null Terminators (\0): c_char_p handles the null termination automatically, so you don't need to add \0 to the byte strings manually. Just use b"193.164.200.1" and b"32407".

  2. Check for a NULL Pointer: The function returns a void*, which is represented by c_void_p in Python. If the connection fails, the return value should be NULL, which in Python should be 0. So, you check if x == 0 to determine if the connection failed.

  3. Handle the Return Value: If the connection is successful, x will be a pointer (represented as an integer). You can print this value or use it for further operations.

Expected Output:

Since you're not connected to the sensor, the output should look like this (or similar depending on your environment):

The Library is loaded
Returned Pointer: 0
Connection failed (NULL pointer returned)

If you successfully connect to the sensor later, the x value will be a non-zero pointer.

Additional Notes:

  • If the sensor or network configuration changes, you may want to ensure the correct IP address, port, and timeout values.
  • If you plan to work with the handle returned by EthernetScanner_Connect in further API calls, make sure the SDK documentation specifies how to manage and release these handles.
  • Depending on the SDK and the environment, the pointer value might appear as a large integer, but that’s normal for pointer-type values.

I hope this helps! Let me know if you need further assistance.

#py