On 5/11/23, Jason Qian via Python-list <python-list@python.org> wrote: > > in the Python, I have a array of string > var_array=["Opt1=DG","Opt1=DG2"] > I need to call c library and pass var_array as parameter > In the argtypes, how do I set up ctypes.POINTER(???) for var_array? > > func.argtypes=[ctypes.c_void_p,ctypes.c_int, ctypes.POINTER(????)] > > In the c code: > int func (void* obj, int index, char** opt)
The argument type is ctypes.POINTER(ctypes.c_char_p), but that's not sufficient. It doesn't implement converting a list of str objects into an array of c_char_p pointers that reference byte strings. You could write a wrapper function that implements the conversion before calling func(), or you could set the argument type to a custom subclass of ctypes.POINTER(ctypes.c_char_p) that implements the conversion via the from_param() class method. https://docs.python.org/3/library/ctypes.html#ctypes._CData.from_param Here's an example of the latter. C library: #include <stdio.h> int func(void *obj, int index, char **opt) { int length; for (length=0; opt[length]; length++); if (index < 0 || index >= length) { return -1; } return printf("%s\n", opt[index]); } Python: import os import ctypes lib = ctypes.CDLL('./lib.so') BaseOptions = ctypes.POINTER(ctypes.c_char_p) class Options(BaseOptions): @classmethod def from_param(cls, param): if isinstance(param, list): new_param = (ctypes.c_char_p * (len(param) + 1))() for i, p in enumerate(param): new_param[i] = os.fsencode(p) param = new_param return BaseOptions.from_param(param) lib.func.argtypes = (ctypes.c_void_p, ctypes.c_int, Options) demo: >>> opts = ['Opt1=DG', 'Opt1=DG2'] >>> lib.func(None, 0, opts) Opt1=DG 8 >>> lib.func(None, 1, opts) Opt1=DG2 9 -- https://mail.python.org/mailman/listinfo/python-list
