Python中的ctypes空指针数组

Question

everyone,

now I am using the model of ctypes in python to introduce a .dll file. In my source code I have a function in c++ as followings

bool getFrameFromStream(char* streamName, const void* framebuffer, int frame_number, int overwriteMaxPixelVal=-1)

where framebuffer is a pointer pointing to an array of pixel data of flexible types, eg char, Uint16, etc. Since I am a newbee for python, I used ctypes.create_stream_buffer, namely

framebuffer = ctypes.create_string_buffer(1000000)
ctypes.cast(framebuffer, ctypes.c_void_p)

My questions is if the usage promises all the elements in the buffer can be of any type? Or just first one element is flexible while the others should still be char? If so, what should I do if I want to transfer a suitable variable.

Many Thanks

Answer 1

If you have a buffer and you want to convert to different types, you should use a struct . For example, if you have:

struct FrameBuffer {
    int a;
    int b;
    double d;
    float g;
}

Then if you have the string that represents this stack in a variable my_data in Python, you could unpack it with the call:

import struct
# ...
mvars = struct.unpack("iidf",my_data);

myvars will be a tuple of the data unpacked from there.

Check the examples in the link I gave you.