(Question correction) Python types, OSError: exception: access violation reading 000000 error

import tkinter as tk
from tkinter import filedialog, ttk, Menu
import ctypes as C
import tkinter.scrolledtext as tkst
from ctypes.util import find_library
from ctypes import *

filename = ""

#Open File Function
def openfile():
    filename = filelog.askopenfilename (initialdir = "C:/Users/administration/source/repos/Read/Read", title = "Please select a file", filetypes = ('RAW file', '*.RAW'), ('all files',*).*"))) the path to the #filename = file
    class foo(C.Structure):
     _fields_=[(filename,c_char_p)]


#calculation button function, this is where the problem occurs.
def clickOK():

         IEEE = C.CDLL('IEEE')
         tole = 0.00005
         c_main = IEEE['main']
         IEEE.main.argtypes = [C.c_double,C.c_char_p]
         IEEE.main(C.c_double(tole), C.c_char_p(filename.encode('utf-8')))  
    #Part of the problem.
         txt = open("IEEE result.txt", 'r')
         data = txt.read()
         scrt.insert(tk.INSERT, data)                   
         scrt.see(tk.END)

#There is no problem because the bottom part is the basic setting. 

if __name__ == '__main__':
    #Title and Size
    win = tk.Tk()
    win.title("Power Flow Simulator")
    win.resizable(True, True)
    #win.geometry("600x400+200+200")                     

    #Inner Label
    labelGender = ttk.Label(win, text="Method:")   
    labelGender.grid(column=0, row=0)               
    labelMargin = ttk.Label(win, text="tolerance:")         
    labelMargin.grid(column=1, row=0)                  

    #MethodFormat
    Method = tk.StringVar()                                         
    MethodCombo = ttk.Combobox(win, width=20, textvariable=Method)   
    MethodCombo['values'] = ("Gauss-Seidel method", "Newton-Raphson method")                      
    MethodCombo.grid(column=0, row=1)
    MethodCombo.current(0)

    #Margin Format
    Margin = tk.IntVar()                                       
    MarginEntered = ttk.Entry(win, width=20, textvariable=Margin)  
    MarginEntered.grid(column=1, row=1)

    #Calculation button
    action = ttk.Button(win, text="Calculate", command=clickOK)    
    action.grid(column=2, row=1)

    #Calculation contents window
    scrt = tkst.ScrolledText(win, width=75, height=15, wrap=tk.WORD)
    scrt.grid(column=0, row=2, columnspan=3)
    scrt.focus_set()                                                

#Menu window format, file
menu_bar = Menu(win)
file_menu = Menu(menu_bar, tearoff = 0)
file_menu.add_command (label = 'Open File', command = openfile)
file_menu.add_separator()
file_menu.add_command (label = 'end', command = win.quit)
menu_bar.add_cascade (label = 'file', menu = file_menu)

#Menu window format, help
file_menu2 = Menu(menu_bar, tearoff = 0)
file_menu.add_separator()
file_menu2.add_command (label = 'information')
menu_bar.add_cascade (label = 'help', menu = file_menu2)
win.config(menu = menu_bar)

tk.mainloop()