[Visual C#] The Hauntings of NullArgumentException

Brauss · 2009-06-02T10:41:50

I have been haunted by the ghost of NullArgumentException. Basically the program I am making is a game menu. It has functions to take a new username and password and write them to files to save them for the next running of the program. However, when I try and run the program when there are no current usernames or passwords, it fails because the file is null(?). This is the function which results in the NullArgumentException: (three blocks of code - one for each character slot) // ----------------------- SHOW THE NAMES static void ShowNames() { System.IO.StreamReader reader; reader = new System.IO.StreamReader(name1); string str1 = reader.ReadLine(); char[] char1 = str1.ToCharArray(); if (char1.Length != 0) System.Console.WriteLine("| 1. ", str1, "|"); else System.Console.WriteLine("| 1. Empty slot |"); reader = new System.IO.StreamReader(name2); string str2 = reader.ReadLine(); char[] char2 = str1.ToCharArray(); if (char1.Length != 0) System.Console.WriteLine("| 1. ", str2, "|"); else System.Console.WriteLine("| 1. Empty slot |"); reader = new System.IO.StreamReader(name3); string str3 = reader.ReadLine(); char[] char3 = str1.ToCharArray(); if (char1.Length != 0) System.Console.WriteLine("| 1. ", str3, "|"); else System.Console.WriteLine("| 1. Empty slot |"); } What the function is meant to do is read all the three username files, and then convert the string result into an array of characters. Then, if the length of the array is 0, I assume no username has been set, so it prints empty slot. Otherwise it prints the string from the file. I have been told that it can be solved by declaring new readers at the top, but this didn't work and kinda resulted in more complications. Here is the whole program (228 lines) if you need it: // ------------------------------------------------------------------------ CLASS public class Game { static string[] characters = new string[3]; static string[] full_characters = new string[3]; static string[] passwords = new string[3]; static bool[] ischaracter = new bool[3]; static bool[] ispassword = new bool[3]; static System.IO.FileStream name1, name2, name3; static System.IO.FileStream pass1, pass2, pass3; // --------------------------------------------------------------------- MAIN static void Main(string[] args) { // ----------------------- START MENU System.Console.WriteLine("Welcome to Odyssey!\n"); System.Console.WriteLine("Choose your character:\n\n"); System.Console.WriteLine("---------------------"); System.Console.WriteLine("| Character name | "); System.Console.WriteLine("|-------------------| "); Game.ShowNames(); System.Console.WriteLine("---------------------"); // ----------------------- TAKE CHARACTER CHOICE AND RESPOND string choice = System.Console.ReadLine(); int choicenum = 0; if (choice == "1") choicenum = 1; if (choice == "2") choicenum = 2; if (choice == "3") choicenum = 3; Game.RespondChoice(choicenum); // ---------------------- SET NEW PASSWORD // ---------------------- TAKE PASSWORD ATTEMPT AND CHECK IT string pass_try = System.Console.ReadLine(); Game.CheckPass(choicenum); } // ---------------------------------------------------------------- FUNCTIONS // ----------------------- SHOW THE NAMES static void ShowNames() { System.IO.StreamReader reader; reader = new System.IO.StreamReader(name1); string str1 = reader.ReadLine(); char[] char1 = str1.ToCharArray(); if (char1.Length != 0) System.Console.WriteLine("| 1. ", str1, "|"); else System.Console.WriteLine("| 1. Empty slot |"); reader = new System.IO.StreamReader(name2); string str2 = reader.ReadLine(); char[] char2 = str1.ToCharArray(); if (char1.Length != 0) System.Console.WriteLine("| 1. ", str2, "|"); else System.Console.WriteLine("| 1. Empty slot |"); reader = new System.IO.StreamReader(name3); string str3 = reader.ReadLine(); char[] char3 = str1.ToCharArray(); if (char1.Length != 0) System.Console.WriteLine("| 1. ", str3, "|"); else System.Console.WriteLine("| 1. Empty slot |"); } // ----------------------- FILL THE NAMES TO WIDTH 15 static void FillChars() { full_characters[0] = characters[0].PadRight(15); full_characters[1] = characters[1].PadRight(15); full_characters[2] = characters[2].PadRight(15); } // ---------------------- RESPOND TO CHARACTER CHOICE static void RespondChoice(int i) { switch (i) { case 1: if (ischaracter[1]) Game.CheckPass(i); else Game.NewName(1); break; case 2: if (ischaracter[1]) Game.CheckPass(i); else Game.NewName(2); break; case 3: if (ischaracter[2]) Game.CheckPass(i); else Game.NewName(3); break; } } // ---------------------- SET NEW CHARACTER NAME static void NewName(int i) { System.Console.WriteLine("Choose your character's name.\n"); System.IO.StreamWriter writer; switch (i) { case 1: name1 = System.IO.File.OpenWrite("name1.txt"); writer = new System.IO.StreamWriter(name1); characters[0] = System.Console.ReadLine(); writer.WriteLine(characters[0]); writer.Close(); ischaracter[0] = true; break; case 2: name2 = System.IO.File.OpenWrite("name2.txt"); writer = new System.IO.StreamWriter(name2); characters[1] = System.Console.ReadLine(); writer.WriteLine(characters[1]); writer.Close(); ischaracter[1] = true; break; case 3: name3 = System.IO.File.OpenWrite("name3.txt"); writer = new System.IO.StreamWriter(name3); characters[2] = System.Console.ReadLine(); writer.WriteLine(characters[2]); writer.Close(); ischaracter[2] = true; break; } Game.NewPass(i); } // ---------------------- SET NEW PASSWORD static void NewPass(int i) { System.Console.WriteLine("Choose your character's password.\n"); System.IO.StreamWriter writer; switch (i) { case 1: pass1 = System.IO.File.OpenWrite("pass1.txt"); writer = new System.IO.StreamWriter(pass1); passwords[0] = System.Console.ReadLine(); writer.WriteLine(passwords[0]); writer.Close(); System.Console.WriteLine("You're in."); break; case 2: pass2 = System.IO.File.OpenWrite("pass2.txt"); writer = new System.IO.StreamWriter(pass2); passwords[1] = System.Console.ReadLine(); writer.WriteLine(passwords[1]); writer.Close(); System.Console.WriteLine("You're in."); break; case 3: pass3 = System.IO.File.OpenWrite("pass3.txt"); writer = new System.IO.StreamWriter(pass3); passwords[3] = System.Console.ReadLine(); writer.WriteLine(passwords[3]); writer.Close(); System.Console.WriteLine("You're in."); break; } } // --------------------- CHECK PASSWORD IS CORRECT static void CheckPass(int i) { string[] attempts = new string[3]; System.Console.WriteLine("Enter your password:\n"); System.IO.StreamReader reader; switch (i) { case 1: reader = new System.IO.StreamReader(pass1); attempts[0] = System.Console.ReadLine(); if (attempts[0] == reader.ReadLine()) System.Console.WriteLine("You're in."); else System.Console.WriteLine("Incorrect password."); break; case 2: reader = new System.IO.StreamReader(pass2); attempts[1] = System.Console.ReadLine(); if (attempts[1] == reader.ReadLine()) System.Console.WriteLine("You're in."); else System.Console.WriteLine("Incorrect password."); break; case 3: reader = new System.IO.StreamReader(pass3); attempts[2] = System.Console.ReadLine(); if (attempts[2] == reader.ReadLine()) System.Console.WriteLine("You're in."); else System.Console.WriteLine("Incorrect password."); break; } } } Any help is greatly appreciated.

For Beginners

Started by Brauss May 30, 2009 03:47 PM

9 comments, last by Zahlman 14 years, 10 months ago

Zahlman

1,682

June 02, 2009 10:41 AM

It could also be System.Console.WriteLine("| 1. {0}|", reader.ReadLine());. :) The idea is that the first argument to System.Console.WriteLine() is a "format" string, and anything else is a value to "substitute into" the format string. In your original code, you were supplying reader.ReadLine() and "|" as things to substitute in, but didn't specify anywhere to substitute them. The {#} parts of the format string indicate where to insert the other arguments - {0} for the first one after the format string, {1} for the next etc. This is described in detail in the MSDN documentation (see also).

But anyway, the point I wanted to make: repetition is the computer's job, not yours.

// We make a helper function first, which takes the file ID and substitutes it// in everywhere that it's needed - into the file name itself, and into the// output text.static void ShowName(int id) {  String fileName = String.format("name{0}.txt", id);  // We initialize the "name" to a default value, and overwrite that if the  // file is present. That way, there is only one statement in the code  // to do the actual printing.  String result = "Empty slot        ";  if (System.IO.File.Exists(fileName)) {    // Use a local variable for the file stream itself. Restrict scope as    // much as possible, in general.    FileStream file = System.IO.File.OpenRead(fileName);    System.IO.StreamReader reader = new System.IO.StreamReader(file);    result = reader.ReadLine();    reader.Close();  }  // Whether or not we read a slot name, we display whatever name we have  // at this point, labelled with the slot ID:  System.Console.WriteLine("| {0}. {1}|", id, result);        }// ----------------------- SHOW THE NAMESstatic void ShowNames() {  // Now all we have to do is loop over the slot IDs.  for (int i = 0; i < 3; ++i) { ShowName(i); }}

See? Much neater.

[Visual C#] The Hauntings of NullArgumentException

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