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unordered_map giving Segmentation fault (core dumped) when calling C++ library from python

i am trying to use https://github.com/Spyros-DC/words-in-some-editdistance/blob/master/my_distance.cpp C++ implementation in python, however i kept receiving Segmentation fault (core dumped). Below is the entire code in python and C++, i have edited small parts of the original library to suit my use case. I have managed to find that when trying to use the unordered_map children.count(remaining_w.at(0)) it is throwing the segmentation fault error. I was wondering if anyone knows what is causing the error. Thank you so much in advance.
#include <iostream>
#include <unordered_map>
#include <string>
#include <fstream>
#include <unordered_set>
#include <vector>
#include <sstream>
#include <typeinfo>
using namespace std;
// using namespace std::chrono;
class trie{
public:
string word;
unordered_map<char, trie*> children;
// this function works
// with the argument flag set to zero
int insert(string w, int flag, string remaining_w = ""){
//the first time we call insert
if(flag == 0)
remaining_w = w;
int the_size = remaining_w.size();
if(children.count(remaining_w.at(0)) == 0){
children[remaining_w.at(0)] = new trie();
}
if(the_size == 0){
word = w;
return 0;
}else{
//the recursive calls with flag one
children[remaining_w.at(0)]->insert(w, 1, remaining_w.erase(0, 1));
return 0;
}
}
};
class AutoCorrect{
public:
// The tree
trie tree;
//the dictionary with the words
const int max_cost = 2;
const int too_big_distance = 10;
void insert(char* word){
ifstream ifp(word);
while(ifp >> word){
cout << word <<endl;
tree.insert(word, 0);
// }
}
}
void test(char* test){
cout << test << endl;
}
void search_recursive(trie* p_tree, char ch, const string& word, vector<int>& previous_row, int max_cost, unordered_map <string, int>& results)
{
int sz = previous_row.size();
int min_row = 12;
vector<int> current_row(sz, too_big_distance);
current_row[0] = previous_row[0] + 1;
// Calculate the min cost of insertion, deletion, match or substution
int insert_or_del, replace;
for (int i = 1; i < sz; i++) {
insert_or_del = min(current_row[i-1] + 1, previous_row[i] + 1);
replace = (word[i-1] == ch) ? previous_row[i-1] : (previous_row[i-1] + 1);
current_row[i] = min(insert_or_del, replace);
}
if ((current_row[sz-1] <= max_cost) && (p_tree->word != "")) {
results[p_tree->word] = current_row[sz-1];
}
for(auto& it: current_row){
if (it < min_row)
min_row = it;
}
if(min_row <= max_cost){
for(auto& it: p_tree->children){
search_recursive(it.second, it.first, word, current_row, max_cost, results);
}
}
}
int search(string word)
{
unordered_map <string, int> results;
int sz = word.size();
vector<int> current_row(sz + 1);
for (int i = 0; i <= sz; ++i){
current_row[i] = i;
}
for(auto& it: tree.children){
search_recursive(it.second, it.first, word, current_row, max_cost, results);
}
for(auto& p:results)
cout << p.first << ", " << p.second << endl;
return 0;
}
};
// The cost and a distance for vector initialization
extern "C" {
AutoCorrect* AutoCorrect_new(){ return new AutoCorrect(); }
void AutoCorrect_insert(AutoCorrect* autocorrect, char* word){ autocorrect->insert(word); }
void AutoCorrect_search(AutoCorrect* autocorrect, string input_word){ autocorrect->search(input_word); }
void AutoCorrect_test(AutoCorrect* autocorrect, char* name){ autocorrect-> test(name); }
}
Python main.py:
from ctypes import cdll
lib = cdll.LoadLibrary('autocorrect.so')
class AutoCorrect(object):
def __init__(self):
self.obj = lib.AutoCorrect_new()
def insert(self, word):
lib.AutoCorrect_insert(self.obj,word)
def search(self,input_word):
lib.AutoCorrect_search(self.obj,input_word)
def test(self,test):
lib.AutoCorrect_test(self.obj,test)
if __name__ == "__main__":
import json
WordCount = 0
autocorrect = AutoCorrect()
data_dir = "some_txt_file.txt"
autocorrect.insert(bytes(str(data_dir), encoding='utf8'))

Looking at the line you specified, i think there is an instance you are trying to add a value to a non existent key:
if(children.count(remaining_w.at(0)) == 0){
children[remaining_w.at(0)] = new trie();
if "children.count" returns 0 then that character is not present, then trying to add a value on the second line there means....
what i think you want to do on that line is:
if(children.count(remaining_w.at(0)) == 1){
children[remaining_w.at(0)] = new trie();
meaning you add the value only if key is present.

How do i fix a throw error when integrating Python and C++ Code? Is the issue with the way that I am calling the function from Python to c++?

Ok so I am trying to run a program that uses C++ and Python. The C++ code calls functions from the Python code. The code in C++ that is above main() was already provided and is not supposed to be edited. However, I keep getting the following error: Unhandled exception thrown: write access violation.
pValue was nullptr. When running the code with options 1 & 2. How do I fix this?
C++ Code
#include <Python.h>
#include <iostream>
#include <Windows.h>
#include <cmath>
#include <string>
#include <string.h>
using namespace std;
void CallProcedure(string pName)
{
char* procname = new char[pName.length() + 1];
std::strcpy(procname, pName.c_str());
Py_Initialize();
PyObject* my_module = PyImport_ImportModule("PythonCode");
PyErr_Print();
PyObject* my_function = PyObject_GetAttrString(my_module, procname);
PyObject* my_result = PyObject_CallObject(my_function, NULL);
Py_Finalize();
delete[] procname;
}
int callIntFunc(string proc, string param)
{
char* procname = new char[proc.length() + 1];
std::strcpy(procname, proc.c_str());
char* paramval = new char[param.length() + 1];
std::strcpy(paramval, param.c_str());
PyObject* pName, * pModule, * pDict, * pFunc, * pValue = nullptr, * presult = nullptr;
// Initialize the Python Interpreter
Py_Initialize();
// Build the name object
pName = PyUnicode_FromString((char*)"PythonCode");
// Load the module object
pModule = PyImport_Import(pName);
// pDict is a borrowed reference
pDict = PyModule_GetDict(pModule);
// pFunc is also a borrowed reference
pFunc = PyDict_GetItemString(pDict, procname);
if (PyCallable_Check(pFunc))
{
pValue = Py_BuildValue("(z)", paramval);
PyErr_Print();
presult = PyObject_CallObject(pFunc, pValue);
PyErr_Print();
}
else
{
PyErr_Print();
}
//printf("Result is %d\n", _PyLong_AsInt(presult));
Py_DECREF(pValue);
// Clean up
Py_DECREF(pModule);
Py_DECREF(pName);
// Finish the Python Interpreter
Py_Finalize();
// clean
delete[] procname;
delete[] paramval;
return _PyLong_AsInt(presult);
}
int callIntFunc(string proc, int param)
{
char* procname = new char[proc.length() + 1];
std::strcpy(procname, proc.c_str());
PyObject* pName, * pModule, * pDict, * pFunc, * pValue = nullptr, * presult = nullptr;
// Initialize the Python Interpreter
Py_Initialize();
// Build the name object
pName = PyUnicode_FromString((char*)"PythonCode");
// Load the module object
pModule = PyImport_Import(pName);
// pDict is a borrowed reference
pDict = PyModule_GetDict(pModule);
// pFunc is also a borrowed reference
pFunc = PyDict_GetItemString(pDict, procname);
if (PyCallable_Check(pFunc))
{
pValue = Py_BuildValue("(i)", param);
PyErr_Print();
presult = PyObject_CallObject(pFunc, pValue);
PyErr_Print();
}
else
{
PyErr_Print();
}
//printf("Result is %d\n", _PyLong_AsInt(presult));
Py_DECREF(pValue);
// Clean up
Py_DECREF(pModule);
Py_DECREF(pName);
// Finish the Python Interpreter
Py_Finalize();
// clean
delete[] procname;
return _PyLong_AsInt(presult);
}
void main()
{
int clicked = 0;
do {
int n = 0;
cout << "1: Display a Multiplication Table" << endl << "2: Double a Value" << endl << "3:
Exit" << endl;
cin >> clicked;
switch (clicked) {
case 1:
{ cout << "Please enter a numerical value . . ."<< endl;
cin >> n;
cout << callIntFunc("(MultiplicationTable)",n); }
break;
case 2:
{cout << "Please enter a numerical value . . ."<< endl;
cin >> n;
int dValue = callIntFunc("(DoubleValue)",n);
cout << "Doubled Value: " << dValue << endl; }
break;
case 3:
cout << "You are now exiting the program!" << endl;
break;
default:
cout << "Please enter a valid selection . . ."<< endl;
break;
}
} while (clicked != 3);
}
Python code
import re
import string
def printsomething():
print("Hello from python!")
def PrintMe(v):
print("You sent me: " + v)
return 100
def MultiplicationTable(v):
v = int(v)
for i in range(1, 11):
print(v, " x ", i, " = ", (v * i))
def DoubleValue(v):
return v * 2
def SquareValue(v):
return v * v

Just modify the python function to return 0 as follows;
def MultiplicationTable(v):
v = int(v)
for i in range(1, 11):
print(v, " x ", i, " = ", (v * i))
return 0

How to call a Python function that uses numpy from C++ code

I have the following Python module (actual module I want to use, has many more functions using numpy and tensorflow), but this is a representative example to reproduce the issue
import numpy as np
def get_random():
return np.random.random()
I want to call the function get_random from the following C++ program:
#include <Python.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[]){
Py_Initialize();
if( !Py_IsInitialized() ){
printf("Initialize failed\n");
return -1;
}
PyRun_SimpleString("import sys");
//append path of numpy lib
PyRun_SimpleString("sys.path.append('/home/uji300/.pyenv/versions/venv/lib/python3.4/site-packages/numpy/core/include')");
PyObject *pName, *pModule, *pDict, *pFunc, *pArgs, *pRet;
pName = PyUnicode_DecodeFSDefault("numpytester");
pModule = PyImport_Import(pName);
if ( !pModule ){
return -1;
}
pDict = PyModule_GetDict(pModule);
if ( !pDict ){
return -1;
}
pFunc = PyDict_GetItemString(pDict, "get_random");
if ( !pFunc || !PyCallable_Check(pFunc) ){
return -1;
}
for( int i = 0; i < 5; ++i ){
printf(" ===========> START CALL PYTHON SCRIPT %d <===========\n", i + 1);
pRet = PyObject_CallObject(pFunc, NULL); // call the function
printf(" ===========> CALLING FINISHED %d <===========\n", i + 1);
double result = PyFloat_AsDouble(pRet); // get the return value by pRet
printf(" ===========> result = %f <===========\n", result);
}
Py_DECREF(pName);
Py_DECREF(pModule);
Py_DECREF(pArgs);
Py_DECREF(pRet);
Py_DECREF(pDict);
// close Python
Py_Finalize();
return 0;
}
The C++ program is then built with CMake and run. The call to the get_random() does not work. It returns -1 every time.
What is the right way to call a python function that uses numpy or tensorflow functions ?

Using Boost to exchange python and C Numpy Array

I followed the tutorial on boost::python::numpy, found that numpy's ndarray and array could be shared inside C ++ code, and I found that using the Boost python example, I could call a python function in C ++ with arguments and return.
My goal is that boost python and python exchange numpy array values.
First, I tried to pass the numpy array to the python code with boost python. However, I only found a way to set the pylist to PyList_SET_ITEM by creating a pylist instead of a numpy array.
In C++
//https://docs.python.org/2.0/ext/buildValue.html
PyObject *Convert_Big_Array(long arr[], int length) {
PyObject *pylist, *item;
pylist = PyList_New(length);
if (pylist != NULL)
for (int i = 0; i < length; i++) {
item = PyLong_FromLong(arr[i]);
PyList_SET_ITEM(pylist, i, item);
}
return pylist;
}
int main() {
long arr[5] = { 4,3,2,6,10 };
// Python 3.x Version
Py_SetPythonHome(L"C:\\Users\\User\\Anaconda3");
PyObject *pName, *pModule, *pDict, *pFunc, *pValue, *presult;
Py_Initialize();
return 0;
}
pDict = PyModule_GetDict(pModule);
pFunc = PyDict_GetItemString(pDict, (char*)"someFunction");
if (PyCallable_Check(pFunc)) {
pValue = Py_BuildValue("(O)", Convert_Big_Array(arr, 5));
PyErr_Print();
presult = PyObject_CallObject(pFunc, pValue);
PyErr_Print();
}
else {
PyErr_Print();
return 0;
}
boost::python::handle<> handle(presult);
std::cout << std::endl << "Python ndarray :" << p::extract<char const *>(p::str(handle)) << std::endl;
Py_DECREF(pValue);
Py_DECREF(pModule);
Py_DECREF(pName);
Py_Finalize();
return 0;
}
In Python
import numpy as np
def someFunction(text):
print(text)
return np.array([1,2,3])
With this code I find it very difficult to pass a very large C int array to Python. Is there a more efficient way?
First, if I can convert a C ++ array to ndarray using np :: from_data and then convert it to PyObject, I think I can pass this object itself to python.
Second, I want to convert PyObject (presult) created with PyObject_CallObject to np :: ndarray format. Now the code is just an example and the output is successful.
In other words, do you know how to convert ndarray (C ++) -> PyObject (C ++), PyObject (numpy c ++) -> ndarray (c ++)?

I got a answer, and post Here for others...
thank you.
//#include <Python.h>
#include <stdlib.h>
#include <boost/python/numpy.hpp>
#include <boost/python.hpp>
#include <iostream>
//
////#define BOOST_PYTHON_STATIC_LIB
//
using namespace boost::python;
namespace np = boost::python::numpy;
//https://stackoverflow.com/questions/10701514/how-to-return-numpy-array-from-boostpython/14232897#14232897
np::ndarray mywrapper() {
std::vector<short> v;
v.push_back(3);
v.push_back(5);
Py_intptr_t shape[1] = { v.size() };
np::ndarray result = np::zeros(1, shape, np::dtype::get_builtin<short>());
std::copy(v.begin(), v.end(), reinterpret_cast<short*>(result.get_data()));
//std::cout <<"C++ Memory Addr : " << std::dec << &result << std::endl;
return result;
}
//https://stackoverflow.com/questions/54904448/boost-python-nullptr-while-extracting-ndarray
int main() {
double t_end = 7;
long arr[5] = { 4,3,2,6,10 };
// Python 3.x Version
Py_SetPythonHome(L"C:\\Users\\YangwooKim\\Anaconda3");
//PyObject *pName, *pModule, *pDict, *pFunc, *pValue, *presult;
Py_Initialize();
np::initialize();
object module = import("__main__");
object name_space = module.attr("__dict__");
exec_file("arbName.py", name_space, name_space);
object MyFunc = name_space["someFunction"];
object result;
//for(int i=0; i<1000000; i++)
result = MyFunc(mywrapper());
//printf("Result is %d\n", PyLong_AsLong(presult));
//np::ndarray py_array = np::from_object(boost::python::object(handle));
//auto k = extract<np::ndarray>();
//np::ndarray k = np::from_object(object);
//np::ndarray k = p::extract<np::ndarray>(object);
//const np::ndarray& ret = k();
auto result_array = extract<numpy::ndarray>(result);
const numpy::ndarray& ret = result_array();
int input_size = ret.shape(0);
short* input_ptr = reinterpret_cast<short*>(ret.get_data());
//std::cout << std::endl
// << "Python ndarray :" << p::extract<char const *>(p::str(object)) << std::endl;
std::cout << std::endl << "Python ndarray :" << input_size << std::endl;
for (int i = 0; i < input_size; ++i)
std::cout <<" " <<*(input_ptr + i) <<std::endl;
//Py_Finalize();
//Py_Finalize();
return 0;
}

How to use coordinates from an input file with prim's algorithm in order to create circles using pygraphics and C++?

I have looked at many many examples of Prim's Algorithm on here and Google and found no real answer to this question... Please excuse my structure of this problem. I'm terrible with how S/O prints things out.
I have an input file "SmallGraph.txt" that contains a set of coordinates and the number of vertices at the top:
9
50 100
100 150
200 150
300 150
350 100
300 50
200 50
100 50
150 100
I'm having a lot of trouble trying to figure out how to get these input items read so that my while loop will be able to print a "circle" for every vertice mentioned above so I can run Prim's algorithm for a minimum spanning tree.
What code I have so far of me attempting to get something printed out with a while loop. Also, a few classes to implement Prim's algorithm with those points I need to plot through python:
#include <cstdlib>
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
#include <cstring>
#include <math.h> /* pow() function */
// This line allows commonly-used functions to be used without specifying the
// library in which that function is defined. For instance, this line allows
// the use of "cout" rather than the full specification "cout"
using namespace std;
class SetOfIntegers
{
public:
// Constructor. Any setup operation you wish for the class.
SetOfIntegers()
{
members.clear();
} // end constructor
void add(int m) // Add members to set WITHOUT repetition
{
for (auto i : members)
{
if (i == m) return; // no addition of existing member
}
members.push_back(m);
}
int size() { return members.size(); }
void show() { for (auto i: members) cout << i << " "; cout << endl; }
bool isMember(int m)
{
//cout << "isMember(" << m << ") is ";
for (auto i : members)
{
if (i == m)
{
//cout << " true" << endl;
return true;
}
}
//cout << " false" << endl;
return false;
}
private:
vector<int> members;
};
//--------------------------------------------------------------------------
class Point
{
public:
// Constructor. Any setup operation you wish for the class.
Point()
{
x = 0; y = 0;
} // end constructor
Point(int a, int b, int id)
{
x = a; y = b; pointID = id;
} // end constructor
int getX() { return x; }
int getY() { return y; }
int getID() { return pointID; }
private:
int x = 0;
int y = 0;
int pointID = 0;
}; // end class Point
//--------------------------------------------------------------------------
class Edge
{
public:
// Constructor. Any setup operation you wish for the class.
Edge()
{
} // end constructor
Edge(Point ptA, Point ptB)
{
pointA = ptA;
pointB = ptB;
length = sqrt(pow(abs(pointA.getX() - pointB.getX() ), 2) + pow(abs(pointA.getY() - pointB.getY() ), 2) );
} // end constructor
Point getPtA() { return pointA; }
Point getPtB() { return pointB; }
double getLen() { return length; }
int getPtAID() { return pointA.getID(); }
int getPtBID() { return pointB.getID(); }
private:
Point pointA;
Point pointB;
double length;
}; // end class Edge
// NOTE: DO NOT declare with empty parentheses, as vector<Point> myPointvector();
vector<Point> myPointvector; // vector will expand as needed
vector<Edge> MinSpanTree;
// Pass arguments or parameters from command-line execution. argc is the count of
// those parameters, including the executable filename. argv[] is an array of the
// parameters.
int main (int argc, char *argv[])
{
string token;
int xValue, yValue;
ifstream fin;
int coordPairs; // number of coordinate pairs in the file
int ptX, ptY;
vector<Edge> unsortedEdgeVector;
vector<Edge> sortedEdgeVector;
int loopCounter;
int pointCounter = 0;
double MSTLength = 0.0;
// Check the number of arguments. Expected: filename of a file
if (argc != 2) // This check is often hardcoded
{ // If failure in parameters, offer advice for correction
cout << "\nThis program uses command-line argument.\n";
cout << "Usage: a.exe <filename>\n";
exit(0);
}
try // All lines within this block are part of the same exception handler
{
fin.open(argv[1]);
}
catch (exception& ex)
{
cout << ex.what(); // display standard explanation of the exception
exit(0); // exit the program
}
// Read from the file, one token at a time. If the type of token is known, it
// can be read into a corresponding variable type, such as
// in >> x; // Read the first item into an integer variable x.
// in >> str; // Read the next item into a string variable str.
//for (int i = 0; 1 != 10; i++) {
// fin >> ptX[2] >> ptY[2];
//}
//cout << ptX << endl;
// This line provides the graphic window setup.
cout << "800 600 white" << endl;
fin >> coordPairs;
while (fin >> ptX)
{
// Do something with the element read from the file
cout << ptX << endl;
fin >> ptY;
cout << ptY << endl;
cout << "circle " << ptX << " " << ptY << " " << 20 << " seagreen" << endl;
/*
Point dummyPoint(ptX, ptY, pointCounter++);
myPointvector.push_back(dummyPoint); // vector will expand as needed
cout << "Now myPointvector has size " << myPointvector.size() << endl;
*/
} // end while
fin.close();
}
As you can see... I have a while loop in my main function that is attempting to create a "circle" based on ptX and ptY. That's what I'm having trouble with.. How do I read from this input file in order to get these points and get them to create a circle through python? If you notice.. I've attempted a for loop that is currently commented out for reading the file.

I was using the wrong command for requesting information from the input file. I was using the commands:
g++ -std=c++11 PrimMSTAlgor.cpp (Compile the code)
a PrimMSTAlgor.cpp > PrimData.dat (Put data into primData.dat from the .cpp file)
python BearPlot.py PrimData.dat (use python to apply graphics)
The second command is incorrect. I need to use the .txt file as the argument for "a" (the execution).
a SmallGraph.txt > PrimData.dat
What I have is already set up to put the input into the .dat file this way, I just couldn't see it...