[英]Python Ctypes passing pointer for data
I am accessing an API and can't get the data returned.我正在访问 API 并且无法获取返回的数据。 The two float pointers will point to an array of data.两个浮点指针将指向一个数据数组。 I must assume the API is working properly.我必须假设 API 工作正常。 A different function call provides a the length of the data I am retrieving.不同的函数调用提供了我正在检索的数据的长度。 This values is length
down below when attempted.尝试时,此值的length
低于此值。
C Header for Function函数的 C 头文件
int function(int, float * data1, float * data2)
ctypes setup ctypes 设置
dll.function.argtypes = (c_int, POINTER(c_float), POINTER(c_float))
dll.function.restypes = c_int
Failed Attempt 1:失败的尝试 1:
x = c_float()
y = c_float()
status = dll.function(1, byref(x), byref(y))
Program crashes OR Access violation writing.程序崩溃或访问冲突写入。
Failed Attempt 2:失败的尝试 2:
x = POINTER(c_float)()
y = POINTER(c_float)()
status = dll.function(1, x, y)
Null Pointer Error空指针错误
Failed Attempt 3:失败的尝试 3:
dll.function.argtypes = (c_int, c_void_p, c_void_p)
x = c_void_p()
y = c_void_p()
status = dll.function(1, x, y)
Null Pointer Error空指针错误
Failed Attempt 4:失败的尝试 4:
array = c_float * length
x = array()
y = array()
status = dll.function(1, byref(x), byref(y))
Program crashes程序崩溃
Failed Attempt 5:失败的尝试 5:
array = c_float * length
x = POINTER(array)()
y = POINTER(array)()
status = dll.function(1, x, y)
Null Pointer Error OR ArgumentError: expected LP_c_float instance instead of LP_c_float_Array_[length]空指针错误或 ArgumentError:预期的 LP_c_float 实例而不是 LP_c_float_Array_[长度]
Failed Attempt 6:失败的尝试 6:
x = (c_float*length)()
y = (c_float*length)()
a = cast(x, POINTER(c_float))
b = cast(y, POINTER(c_float))
status = dll.function(1, a, b)
Program crashes程序崩溃
What am I missing and why?我错过了什么,为什么?
I believe the argtypes are correct.我相信 argtypes 是正确的。 I am attempting to meet them properly, but there continues to be an issues.我试图正确地与他们会面,但仍然存在问题。 Do I need to "malloc" the memory somehow?我需要以某种方式“分配”内存吗? (I'm sure I need to free after I get the data). (我确定我在获得数据后需要释放)。
This is on Windows 7 with Python 2.7 32-bit.这是在带有 Python 2.7 32 位的 Windows 7 上。
I have looked through other similar issues and am not finding a solution.我已经查看了其他类似的问题,但没有找到解决方案。 I am wondering if, at this point, I can blame the API for this issue.我想知道在这一点上,我是否可以将这个问题归咎于 API。
Dealing with pointers and arrays is explained in [Python.Docs]: ctypes - Type conversions . [Python.Docs]: ctypes - Type conversions 中解释了处理指针和数组。
I prepared a dummy example for you.我为你准备了一个虚拟示例。
main00.c :主00.c :
#if defined(_WIN32)
# define DECLSPEC_DLLEXPORT __declspec(dllexport)
#else
# define DECLSPEC_DLLEXPORT
#endif
static int kSize = 5;
DECLSPEC_DLLEXPORT int size() {
return kSize;
}
DECLSPEC_DLLEXPORT int function(int dummy, float *data1, float *data2) {
for (int i = 0; i < kSize; i++) {
data1[i] = dummy * i;
data2[i] = -dummy * (i + 1);
}
return 0;
}
code00.py :代码00.py :
#!/usr/bin/env python
import sys
import ctypes as ct
c_float_p = ct.POINTER(ct.c_float)
def main(*argv):
dll = ct.CDLL("./dll00.so")
size = dll.size
size.argtypes = []
size.restype = ct.c_int
function = dll.function
function.argtypes = [ct.c_int, c_float_p, c_float_p]
function.restype = ct.c_int
sz = size()
print(sz)
data1 = (ct.c_float * sz)()
data2 = (ct.c_float * sz)()
res = function(1, ct.cast(data1, c_float_p), ct.cast(data2, c_float_p))
for i in range(sz):
print(data1[i], data2[i])
if __name__ == "__main__":
print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))
rc = main(*sys.argv[1:])
print("\nDone.")
sys.exit(rc)
Notes :注意事项:
Output (on Lnx , as building the C code is much simpler, but works on Win as well):输出(在Lnx 上,因为构建C代码要简单得多,但也适用于Win ):
[cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q050043861]> gcc -shared -o dll00.so main00.c [cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q050043861]> python3 code00.py Python 3.8.5 (default, Jan 27 2021, 15:41:15) [GCC 9.3.0] 64bit on linux 5 0.0 -1.0 1.0 -2.0 2.0 -3.0 3.0 -4.0 4.0 -5.0
It really depends on what you are doing with these float pointers.这真的取决于你用这些浮点指针做什么。
If you are trying to traverse it, ie如果你试图遍历它,即
for(int i = 0; i < size; i++)
printf("%f\n%, data1[i])
then for sure this is problematic as no array was allocated.那么肯定这是有问题的,因为没有分配数组。 You simply passed a pointer pointing to a float.您只需传递一个指向浮点数的指针。 That is all.就这些。
You need to first allocate that memory.您需要先分配该内存。 To this end Attempt 4 looks like the more promising, but I suspect you have a problem inside your C function leading to the crash.为此,尝试 4 看起来更有希望,但我怀疑您的 C 函数内部有问题导致崩溃。
Difficult to say without seeing the implementation of that function.如果没有看到该功能的实现,很难说。
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