Thread: String Class

Originally Posted by BKurosawa

Can you look at the code below to see if this is correct?

Code:

String& String::operator ++()
{
	buf[stringlength] = 'X';
	stringlength++;
	temp = new char[stringlength];
	strcpy(temp, buf);
	return *this;
}

I suggest that you allocate the bigger buffer first, then copy the string, then set the last char to "X".

And it's definitely not doing what you described (but for some reason I quoted DaveD's post rahter than the original poster):

I have to have it. The ++ operators are supposed to add one to each character in the string literal pointed at by buf. The --operators subtract one from each character.
Does anybody seen any errors or have any other suggestions?

Your code adds one to the LENGTH of the string, and appends an "X" on the end of the string - or at least it looks like that's what you were trying to do, but did things a little bit wrong order - I can't see how that is of any use to anyone (not that adding/subtracting one from each character is particularly useful either, unless you are using it for very basic encryption).

--
Mats

Originally Posted by Daved

That's the idea, but it's not quite correct yet. You are replacing the terminating null character with 'X', strcpy needs the terminating null to know how many characters to copy, so by replacing the null character you will confuse strcpy and you will read and write past the bounds of your arrays.

Then what do I need to do to fix it

Do you have any ideas?

The problem is that by adding the 'X' at the beginning, you are corrupting the string so that it doesn't copy correctly. Does that help give you a clue as to a solution?

Originally Posted by Daved

Do you have any ideas?

The problem is that by adding the 'X' at the beginning, you are corrupting the string so that it doesn't copy correctly. Does that help give you a clue as to a solution?

What needs to be put there instead of the 'X'? earlier you said that the 'X' is bad because it is replacing the null character.

You need to consider the order you are doing things in. Inserting an X is fine, as long as you are not destroying anything valuable. In your implementation you are writing X over the "nul" that is ending the string, which can lead to ALL sorts of trouble.

Also, if you insert an X, you need to make sure the NEXT char is a NUL.

--
Mats

Originally Posted by matsp

You need to consider the order you are doing things in. Inserting an X is fine, as long as you are not destroying anything valuable. In your implementation you are writing X over the "nul" that is ending the string, which can lead to ALL sorts of trouble.

Also, if you insert an X, you need to make sure the NEXT char is a NUL.

--
Mats

Can I completely delete the first line in the code?

Well, that wouldn't really work that well either, would it. The stringlength is now longer, but the ACTUAL string is one shorter than stringlen says, which is probably not what someone wanted if they called this function expecting the string to grow (now, WHY anyone would want a string to expand with an X is a different story).

--
Mats

Originally Posted by matsp

Well, that wouldn't really work that well either, would it. The stringlength is now longer, but the ACTUAL string is one shorter than stringlen says, which is probably not what someone wanted if they called this function expecting the string to grow (now, WHY anyone would want a string to expand with an X is a different story).

--
Mats

I guess I do not want to expand the string with an X. All I want to do is to have the value 1 be added to each character in the string literal pointed at by buf

Originally Posted by laserlight

Loop over the characters and add 1 to each character. Still, this sounds like an abuse of operator++ as a named free function would be more descriptive (what does it mean to add 1 to a string? Oh, you actually want to add 1 to each character). Why must you do it this way, anyway? Homework from a teacher who does not know about good class interface design?

I am unsure as to how to implement 1 being added to each character.

Originally Posted by laserlight

What part are you unsure of? The loop, adding 1, or both?

Well, I don't think I should be doing this: stringlength++. Should I be? Do I just make a loop that goes through every single character of buf and add one to it? If that is the case, then how do I add one to each character?

Originally Posted by laserlight

That adds one to the string length. You do not want to change the string length, you want to change each individual character in the string.


Yes.


You can increment the first character with ++buf[0]. I'll leave you to figure out the rest

should i just scrap my entire code for that operator and start over?