problem with getline() file I/O

[sorry the title is misleading/incorrect. I edited my post, but couldnt change the title]
Hi all, I'm having a problem with a function that is supposed to reverse a string. When i Run it, I'm getting a box that says

Quote:

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the instruction at "some hex address" referenced memory at "some other hex address." The memory could not be "written"

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Thanks for any help you can give me

Here is my code

Code:

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string szReverse(string szString)
{
        string szNewString;
        int iLength = szString.length();
        for (int i = 0; i < iLength; i++)
        {
                szNewString[i] = szString[iLength - i - 1];
        }
       
        return szNewString;
}

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that is most likely because you are trying to read and write the same array element. If you have an odd number of elements i will be the same as string.length-i-1 when they meet in the middle. You won't ever write the first half into the second half either, because you'll have already written over the first half of the elements with new data. Use a second string store your reversed string.

>Use a second string store your reversed string.
He did already. I think it's probably because when you instantiate "szNewString", it's empty (it's length() = 0). Try, first, to set its length equal to "szString", and then copy it.

Standard containers such as vector and string are not like their builtin equivalents (arrays if you were wondering). You can declare and use a container before it has any elements, they grow dynamically. You cannot use the subscript operator of a standard container if the element does not already exist. In your case, you can either resize szNewString manually:

Code:

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string szReverse(string szString)
{
  string szNewString;
  int iLength = szString.length();

  szNewString.resize(iLength);
  for (int i = 0; i < iLength; i++)
  {
    szNewString[i] = szString[iLength - i - 1];
  }

  return szNewString;
}

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Or build it dynamically instead of treating it as you would an array:

Code:

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string szReverse(string szString)
{
  string szNewString;
  int iLength = szString.length();

  for (int i = 0; i < iLength; i++)
  {
    szNewString += szString[iLength - i - 1];
    // or
    // szNewString.push_back ( szString[iLength - i - 1] );
  }

  return szNewString;
}

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See also Uses and Abuses of Vector for a similar discussion.

Minor nit, a prefix of "sz" implies "null terminated char *" in hungarian notation. This convention is, of course, pure evil, but can be confusing. str[3] = str[3] is perfectly acceptable, though it does nothing interesting.