I want to learn to create DLLs in c++ and use them in python to increase the speed of calculations. To begin with, I tried to create a simple C++ dll and load it in Python using ctypes, but I get OSError: [WinError 126]:

Traceback (most recent call last): 
File "C:/Users/unknown/Documents/Work_Pyth/tests/test.py", line 4, in <module> lib = CDLL("tdll.dll") File "C:\Program Files (x86)\Python36\lib\ctypes_init_.py", line 348, in init self._handle = _dlopen(self._name, mode) OSError: [WinError 126] The specified module was not found 

DLL code main.h

#ifndef __MAIN_H__
#define __MAIN_H__
#include <windows.h>
#define DLL_EXPORT __declspec(dllexport)
extern "C" void DLL_EXPORT fun(double* in,long len);
#endif

DLL code main.cpp

#include "main.h"
double * v;
extern "C" void DLL_EXPORT fun(double* in,long len)
{
    v=new double[len];
    for (long ii=0; ii<len; ii+=1){
        v[ii]=ii;
    }
    for (long ii=0; ii<len; ii+=1){
        in[ii]=v[ii];
    }
    delete v;
}
extern "C" DLL_EXPORT BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
    return TRUE;
}

In real code the DLL will need to use temporary arrays, so the test DLL contains an intermediate array v. I compile DLL using CodeBlocks with mingw:

-------------- Build: Release in tdll (compiler: GNU GCC Compiler)---------------

g++.exe -fPIC -O -Wall -fPIC -DBUILD_DLL -O -fPIC  -c C:\Users\unknown\Documents\Work_Cpp\tdll\main.cpp -o obj\Release\main.o

How do i use the DLL, Python code

from ctypes import *
import numpy as np

lib = CDLL("tdll.dll")
len=5
v=np.zeros(len)
print(v)
lib.fun.restype=c_void_p
lib.fun.argtypes=(np.ctypeslib.ndpointer(dtype=np.float64),  c_long)
lib.fun(v,len)
print(v)

Why does the error OSError: [WinError 126] occur? I don't think it can be caused by dependencies. Is it possible to use new and delete operators in DLL code? Thanks for any help.