关于python调用c++动态库dll时的参数传递问题

#include <iostream>
extern "C" __declspec(dllexport) int get_str_length(char *str);
int get_str_length(char *in_str)
{
	std::string str(in_str);
	return str.length();
}

import ctypes as C
dll = C.cdll.LoadLibrary('VS_create_dll.dll')
#4.1 传入字符串调用demo 方法一
p_str = C.c_char_p(b'hello')#或p_str =  b'hello'
str_length1 = dll.get_str_length(p_str)
print("传入字符串调用demo 方法一:")
print (str_length1)
#4.1 传入字符串调用demo 方法二
get_str_length = dll.get_str_length
get_str_length.argtypes = [C.c_char_p]
get_str_length.restype = C.c_int
str_length2 = get_str_length(p_str)
print("传入字符串调用demo 方法二:")
print (str_length2)

python: 	C.POINTER(C.c_ubyte)
C++:		unsigned char *

import ctypes as C
import cv2
img = cv2.imread('ROI0.png')
#将img转换成可被传入dll的数据类型
img.ctypes.data_as(C.POINTER(C.c_ubyte))

Mat src = Mat(rows,cols,CV_8UC3,src_data);

src.data

memcp(ret_data,src.data,rows*cols*3);

#声明并初始化变量
import numpy as np
import cv2
ret_img = np.zeros(dtype=np.uint8, shape=(rows, cols, 3))
#call dll,ret_img.ctypes.data_as(C.POINTER(C.c_ubyte))作为参数传入
cv2.imshow("result",ret_img )

#include "stdafx.h"
#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace cv;
using namespace std;
extern "C" __declspec(dllexport) void draw_circle(int rows, int cols, unsigned char *src_data, unsigned char *ret_data);
void draw_circle(int rows, int cols, unsigned char *src_data , unsigned char *ret_data)
{
	//将unsigned char转换成Mat
	Mat src = Mat(rows, cols, CV_8UC3, src_data);
	//在图像上画一个蓝色的圆
	circle(src, Point(60, 60), 10, Scalar(255, 0, 0));
	//将Mat转换成unsigned char
	memcpy(ret_data, src.data, rows*cols * 3);
}

import ctypes as C
import cv2
import numpy as np
dll = C.cdll.LoadLibrary("draw_circle.dll")
img = cv2.imread('ROI0.png')
(rows, cols) = (img.shape[0], img.shape[1])
ret_img = np.zeros(dtype=np.uint8, shape=(rows, cols, 3))
dll.draw_circle(rows, cols, img.ctypes.data_as(C.POINTER(C.c_ubyte)), ret_img.ctypes.data_as(C.POINTER(C.c_ubyte)))
cv2.imshow("src with circle",ret_img)
cv2.waitKey(0)