python dll 数组,带有DLL的Python ctypes参数-指向双精度数组的指针

朱雀 2023-01-24 03:29 16阅读 0赞

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I am a newbie coder working with ctypes in Python, and attempting to use functions from a DLL written in C. I have found a lot of similar questions to mine on SO but nothing that answers this type of conundrum.

I have loaded the DLL just fine, but one of the functions I need to call asks for a pointer to an array of 6 doubles to dump values into, and I cannot figure out how to give the function what it needs via Python. (My failed attempts to just do this in C are another story.)

I've tried various permutations of ctypes.POINTER(c\_double), using byref(), POINTER(c\_double \* 6), etc and I get type errors at worst, or access violations at best, for all of them.

From the DLL documentation:

int swe\_calc\_ut (double tjd\_ut, int ipl, int iflag, double\* xx, char\* serr)

The function does calculations using the time in Julian Days to return the longitude, latitude, etc, of a planetary body as doubles.

The closest I've gotten to passing in data types that the DLL will accept is using this code, just trying to get any of the 6 doubles out of swe\_calc\_ut:

dll = windll.LoadLibrary(\# file path)

\# retype the args for swe\_calc\_ut

py\_swe\_calc\_ut = dll.swe\_calc\_ut

py\_swe\_calc\_ut.argtypes = \[c\_double, c\_int, c\_int, c\_double, c\_char\_p\]

py\_swe\_calc\_ut.restype = None

tjd = c\_double(\# some value from elsewhere)

returnarray = c\_double()

errorstring = create\_string\_buffer(126)

py\_swe\_calc\_ut(tjd, c\_int(0), c\_int(64\*1024), returnarray, errorstring)

When I try to run this as-is, I get the error:

OSError: exception: access violation writing 0x0000000000000000

Using byref() gives me a type error, etc.

If anyone could point me in the right direction for getting the desired doubles out of the original DLL function, I would be eternally grateful; I'm stumped and can't get this off the ground.

解决方案

This (untested) should work. The 4th parameter is type POINTER(c\_double). The equivalent of C's double returnarray\[6\] type is c\_double \* 6 and an instance of that type is returnarray= (c\_double \* 6)(). Also, if you've declared the argument types you don't need to wrap the input parameters such as int(0); passing 0 is fine:

dll = windll.LoadLibrary(\# file path)

\# retype the args for swe\_calc\_ut

py\_swe\_calc\_ut = dll.swe\_calc\_ut

py\_swe\_calc\_ut.argtypes = \[c\_double, c\_int, c\_int, POINTER(c\_double), c\_char\_p\]

py\_swe\_calc\_ut.restype = None

tdj = 1.5 \# some value

returnarray = (c\_double \* 6)()

errorstring = create\_string\_buffer(126)

py\_swe\_calc\_ut(tjd, 0, 64\*1024, returnarray, errorstring)

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