I'm trying to open a dll written in c with python ctypes and run the function in it, but it comes as a char, not a string

Question

這些是我正在處理的代碼：

#include <stdio.h>

void test_print(char test[100])
{
        printf("%s", test);
}

from ctypes import *
libcdll = CDLL("test.dll")

libcdll.test_print("test")

但是當我運行程序時，我得到的是“t”而不是“test”。

Answer 1

總是為你的函數設置.argtypes和.restype來避免頭痛。 ctypes可以驗證 arguments 是否正確傳遞。

例子：

測試.c

#include <stdio.h>

__declspec(dllexport)        // required for exporting a function on Windows
void test_print(char* test)  // decays to pointer, so char test[100] is misleading.
{
        printf("%s", test);
}

測試.py

from ctypes import *
libcdll = CDLL("./test")
libcdll.test_print.argtypes = c_char_p,  # for (char*) arguments, comma makes a tuple
libcdll.test_print.restype = None       # for void return
libcdll.test_print(b"test")

output：

test

如果在 OP 問題中使用“test”調用，現在它會告訴您參數錯誤：

Traceback (most recent call last):
  File "C:\test.py", line 5, in <module>
    libcdll.test_print("test")
ctypes.ArgumentError: argument 1: <class 'TypeError'>: wrong type

Without .argtypes , ctypes defaults to converting "test" from a Python str to a wchar_t* encoded as UTF-16LE on Windows, so it would look like the following, and printf will stop at the first null byte ( \x00 ), explaining t作為 output。

>>> 'test'.encode('utf-16le')
b't\x00e\x00s\x00t\x00'

請注意，如果您想傳遞 Python str而不是bytes ，請聲明 C function 如下並使用.argtypes = c_wchar_p, ：

void test_print(wchar_t* test) {
        wprintf(L"%s", test);  // wide version of printf and format string
}