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Learn how to interact with Windows DLLs and call functions from them using Python’s ctypes module.

# Python ctypes.c_int.in_dll Usage

## Overview
In this guide, we will explore the usage of `ctypes.c_int.in_dll` in Python. The `ctypes` module in Python provides a way to work with C data types and call functions from shared libraries such as DLLs. We will look at examples of loading a Windows DLL using `LoadLibrary` and invoking functions from it.

### Loading a Windows DLL
To load a Windows DLL using `LoadLibrary`, you can use the following APIs in Python:
“`python
import ctypes
ctypes.windll.LoadLibrary(name)
ctypes.oledll.LoadLibrary(name)
“`
For loading regular DLLs, you can use `WinDLL` instance’s `LoadLibrary`, and for OLE DLLs, you can use `OleDLL` instance’s `LoadLibrary`. Sometimes, errors like `OSError: [WinError 193] %1 is not a valid Win32 application` may occur when calling a DLL that is not compatible with the Python environment (e.g., 64-bit Python calling a 32-bit DLL).

### Calling Functions from DLL
Let’s consider a DLL source with the following API examples:
“`c
int xl_square(int x) { return x * x; }
int xl_square_out(int x, int *result) {
if (result) {
*result = x * x;
return 0;
}
return -1;
}
void xl_callback(callback cb) {
if (!cb) return;
for (int i = 0; i < 10; i++) { cb(i * i); } } ``` When calling these functions from Python, you can follow these steps: 1. For a regular function call: ```python dll = ctypes.windll.LoadLibrary('xl.dll') xl_square = dll.xl_square xl_square.argtypes = (ctypes.c_int,) xl_square.restype = ctypes.c_int result = xl_square(10) ``` 2. For functions with pointer arguments: ```python dll = ctypes.windll.LoadLibrary('xl.dll') xl_square_out = dll.xl_square_out xl_square_out.argtypes = (ctypes.c_int, ctypes.POINTER(ctypes.c_int)) xl_square_out.restype = ctypes.c_int result = ctypes.c_int() xl_square_out(10, ctypes.byref(result)) ``` 3. For functions with a callback function pointer: ```python dll = ctypes.windll.LoadLibrary('xl.dll') callback_type = ctypes.WINFUNCTYPE(None, ctypes.c_int) xl_callback = dll.xl_callback xl_callback.argtypes = (callback_type,) xl_callback.restype = None def cb_func(val): print('cb:', val) xl_callback(callback_type(cb_func)) ``` ### Sample Python Code Here is a sample Python code snippet that demonstrates loading a DLL, calling functions, and using callback functions: ```python import ctypes class xldll(object): def __init__(self): self.dll = ctypes.windll.LoadLibrary('xl.dll') self.xl_square = getattr(self.dll, 'xl_square') self.xl_square.argtypes = (ctypes.c_int,) self.xl_square.restype = ctypes.c_int self.xl_square_out = self.dll.xl_square_out self.xl_square_out.argtypes = (ctypes.c_int, ctypes.POINTER(ctypes.c_int)) self.xl_square_out.restype = ctypes.c_int self.callback_type = ctypes.WINFUNCTYPE(None, ctypes.c_int) self.xl_callback = self.dll.xl_callback self.xl_callback.argtypes = (self.callback_type,) self.xl_callback.restype = None def cb_func(val): print('cb:', val) if __name__ == "__main__": xl = xldll() print(xl.xl_square(10)) result = ctypes.c_int() print(result) print(xl.xl_square_out(10, ctypes.byref(result))) print(result) xl.xl_callback(xl.callback_type(cb_func)) ``` This code snippet shows how to interact with a DLL using `ctypes` in Python, including calling functions with various argument types and using callback functions. By following these guidelines, you can effectively use `ctypes.c_int.in_dll` in Python to work with Windows DLLs and call functions from them.