From: "Lark" <rlark DOT at DOT mbhs DOT dot DOT edu AT delorie DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Weird char * mishaps
Date: Thu, 1 Apr 1999 09:36:49 -0800
Organization: MindSpring Enterprises
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Message-ID: <7e00s5$g94$1@camel0.mindspring.com>
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com


I made a hangman game the other day because I was extremely, extremely
bored.  It works fine, except for one thing:  after I print out the
remaining letters, 4 or 5 weird random letters are printed.  This is a total
stumper.  I am positive I initialized all of my char *s to the correct
number of elements, and I just can't think of anything else that could cause
an error like this.  I am almost absolutely sure that I never access an
element out of bounds or anything.  This is how the program works:

It uses a class called answer, ie the answer to the puzzle, to control what
the user can see and what he/she can't.  It has a member char * word, which
stores the answer, and a member char * mask, which holds a bunch of '-'s or
spaces.  Then it has an unmask function, whose only parameter is a single
character, and it takes the '-'s out of mask that are covering that
character in word.  It returns the number of letters it uncovered.  Here is
the source code:

file://header file containing answer class:
file://header file for hangman.cpp

#include <string.h>
file://strlen(char *), returns length of string

class answer
{
  public:
    answer(char *);
    ~answer();
    int unmask(char);
    int unmasked();
    operator char *();

  private:
    char * word;
    char * mask;
    int length;
    int masked;
};

answer::answer(char * string)
file://PRECONDITIONS : none
file://POSTCONDITIONS : word = string, mask is the length of string with all
alphabetic
//                 characters '-'d out, length = length of string, masked =
#masked
//                 characters.
{
  masked = 0;
  length = strlen(string);
  word = new char[length];
  word = string;
  mask = new char[length];
  for (int i = 0; i < length; i++)
    if (((word[i]>='a') && (word[i]<='z')) || ((word[i]>='A') &&
(word[i]<='Z')))
    {
      mask[i] = '-';
      masked++;
    }
    else
      mask[i] = ' ';

}

answer::~answer()
{
  delete mask; mask = 0;
  delete word; word = 0;
  length = 0;
}

int answer::unmask(char index)
file://PRECONDITONS: this has been initialized(answer())
file://POSTCONDITIONS: every index of word which has index is taken out of
mask,
masked
//                is updated
{
  int numberOfOccurences = 0;
  char indexlow, charlow;        file://To make sure that 'I' unmasks 'i'

  indexlow = index;
  if ((index >= 'A') && (index <= 'Z'))
    indexlow = index - 'A' + 'a'; file://gets the lowercase of index

  for (int i = 0; i < length; i++)
  {
    charlow = word[i];
    if ((word[i] >= 'A') && (word[i] <= 'Z'))
      charlow = word[i] - 'A' + 'a';//gets the lowercase of word[i]

    if (charlow == indexlow)
    {
      numberOfOccurences++;
      masked--;
      mask[i] = ' ';
    }
  }

  return numberOfOccurences;
}

answer::operator char *()
file://PRECONDITIONS:  this is initialized
file://POSTCONDITIONS: word is returned, with mask superimposed on top of
it.
{
  char * final = new char[length];
  for (int i = 0; i < length; i++)
    if (mask[i] == '-')
      final[i] = '-';
    else
      final[i] = word[i];
    cout << "||||||||||" << length << "||";
  return final;
}

int answer::unmasked()
file://returns true if word is completely unmasked
{
  if (masked == 0)
    return 1;
  else
    return 0;
}

/////////////////////////////////////////////////
hangman.cpp
/////////////////////////////////////////////////

#include <iostream.h>
#include "hangman.h"

int main()
{
  answer word("I like this.  It even does capitals!");
  int trysLeft = 10;
  char guess;

  while ((trysLeft > 0) && (!word.unmasked()))
  {
    cout << word << "  :  You have " << trysLeft << " trys left. Pick a
letter: ";
    cin >> guess;
    if (word.unmask(guess) == 0)
    {
      cout << "Sorry, wrong" << endl;
      trysLeft--;
    }
  }

  return 0;
}



Thank you so much for even reading this far.  Has this happened to anyone
else?  A similar error is happening in another program that uses a char *.
Any help at all will be greatly appreciated.  Thanks again!