---
title: c++ call python function
tags: c++, python
description: c++ compress images into unsigned char and sending parameters to python function
---

# c++ call python function
python is writen by c++, so c++ and python should be able to call each function. The example use c++ to read image and call python function to save the image. Python.h is included in python normal installation. It provide interaction between c++ and python.

## Build necessary package
### Build opencv from source for c++
Opencv4 CMakeLists.txt -> OPENCV_GENERATE_PKGCONFIG option default is OFF, change to ON.

**CMakeLists.txt**

...
OCV_OPTION(OPENCV_GENERATE_PKGCONFIG  "Generate .pc file for pkg-config build tool (deprecated)" OFF)
...

Add Opencv4.4.0 PKG_CONFIG_PATH to system

$ export PKG_CONFIG_PATH=/opencv-4.4.0/build/unix-install:$PKG_CONFIG_PATH

### Install opencv-python for python

$ pip3 install opencv-python

## python scipt

**inference.py**

import numpy as np
import cv2

def arrayreset(image):
  b = image[:,:,0]   
  g = image[:,:,1]
  r = image[:,:,2]

  b = np.expand_dims(b, axis=2)
  g = np.expand_dims(g, axis=2)
  r = np.expand_dims(r, axis=2)
  image = np.concatenate((b, g, r), axis=2)

  return image

def load_image(image):
  img = arrayreset(image)
  cv2.imwrite("test.jpg",img)

## c++ scipt

**main.cpp**

#include <iostream>
#include <Python.h>
#include <opencv2/opencv.hpp>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include </usr/local/lib/python3.6/dist-packages/numpy/core/include/numpy/arrayobject.h>

int transport()
{
	Py_Initialize();
	import_array();
  
	PyObject* sys = PyImport_ImportModule("numpy");
  
	PyRun_SimpleString("import sys"); // 执行 python 中的短语句
	PyRun_SimpleString("sys.path.append('./')");

	PyObject *pModule(0);
	pModule = PyImport_ImportModule("inference");//myModel:Python文件名  
  
	cv::Mat img = cv::imread("2.jpg");
  
	int m, n;
	n = img.cols*3;
	m = img.rows;

	unsigned char *data = (unsigned char*)malloc(sizeof(unsigned char) * m * n);
	int p = 0;
	for (int i = 0; i < m; i++)
	{
		for (int j = 0; j < n; j++)
		{
			data[p] = img.at<unsigned char>(i, j);
			p++;
		}
	}
  
	npy_intp Dims[3] = {img.rows, img.cols, 3}; //给定维度信息
	PyObject *PyArray = PyArray_SimpleNewFromData(3, Dims, NPY_UBYTE, data);
	PyObject *pDict = PyModule_GetDict(pModule);
	PyObject *ArgArray = PyTuple_New(1);
	PyTuple_SetItem(ArgArray, 0, PyArray);
	PyObject *pFuncFive = PyDict_GetItemString(pDict, "load_image");
	PyObject_CallObject(pFuncFive, ArgArray);
  
}

int main()
{
	transport();
	system("pause");
	return 0;
}

Build main.cpp

$ g++ main.cpp -o main -I/usr/include/python3.6m/ -lpython3.6m  `pkg-config --cflags --libs opencv4`

execute ./main to call python function

$ ./main

## Reference
* https://blog.csdn.net/qq_41623632/article/details/114600403
* https://blog.csdn.net/qq_38109843/article/details/87969732

## Thank you! :dash:

You can find me on
- GitHub: https://github.com/shaung08
- Email: [e-mail]