A string comparison function

harryp · 09-04-2002

No, this is not a question! I'm just informing everyone I wrote a pretty good string comparison function which I think is a bit more powerful than strcmp(). For instance, strcmp() doesn't return false if the second string has spaces where the first doesn't. I've fixed this. Here's the code, it's pretty basic. It returns true if string 2 is the same as string 1, and false if it is different:

Code:

bool StrComp(char * str1, char * str2)
{
	// loops through and checks, char by char, if equal
	int i=0;
	bool fail=false;

	for( ;; )
	{
		// quit if str1[i] != str2[i]
		if (str1[i] != str2[i])
		{
			fail = true;
			break;
		}
		// this will even fail if str1[i] is a space and str2[i] isn't, unlike strcmp()
		if (str1[i] == ' ' && str2[i] != ' ')
		{
			fail = true;
			break;
		}
		// quit if reach end of string
		if (str1[i] == '\0')
		{
			// return false if only one of the strings is done
			if (str2[i] == '\0')
				break;
			else
			{
				fail = true;
				break;
			}
		}
		i++;
	}
	// fail
	if (fail)
		return false;
	// dont fail
	else
		return true;
}

Just wanted to share that with everyone. I've found a little useful. I've got this thing with using pre-made functions. If I can, I always like to things my own way. Like with this: I'd much rather use something I personally created than something that the compiler includes. It makes me feel good that I can do something just as good as theirs. I'm wierd that way

Anyways, hope you like it.

Brendan

**jdinger** · 09-04-2002

Originally posted by harryp
I'm wierd that way

Not weird at all. It's a great learning tool to design/implement your own functions for common tasks. Not to mention the confidence boost you get from successfully doing it. Good work!

**Sebastiani** · 09-04-2002

That's cool, but a couple of minor problems. For one, strcmp doesn't return true or false. It returns 0 if they match, negative if the second is greater, positive otherwise. But anyhow I know what you meant

By the way, since you are tesing for equality in the first 'if', there is no need for the second if statement. Moreover, you can also return right from the loop if it 'fails'. Here's an example:

bool foo( char *a, char *b)
{
for( int i = 0; a[i] != 0 && b[i] != 0; i++)
{
if(a[i] != b[i]) return false;
}

if(a[i] != b[i]) return false; //...only one was null terminated..

return true;
}

harryp · 09-05-2002

Yeah, I know about the strcmp

. Anyways, I did need the second if because, just like strcmp, if the user enters a space as the last character of their string, and the second string does not have that space, it still says they're the same. And puting the second inside the first wouldn't work either because it doesn't say it's wrong in the first place. So I modified it alightly to this:

Code:

if (str1[i] != str2[i] || str1[i] == ' ' && str2[i] != ' ')
     return false;

That shortened it a lot. And about returning false right away, I was going to do that, but I didn't know if I could do that in a loop. I thought I had to break it first. Oh well, so I learned something. Thanks!

Brendan

**Hammer** · 09-05-2002

Another strcmp version:

Code:

/* strcmp:  return <0 if s<t, 0 if s==t, >0 if s>t */
   int strcmp(char *s, char *t)
   {
       for ( ; *s == *t; s++, t++)
           if (*s == '\0')
               return 0;
       return *s - *t;
   }

(Taken from K&R2, btw).

**Sebastiani** · 09-05-2002

Good ole k&r

i really like that version best.

**swoopy** · 09-05-2002

There's nothing wrong with making your own string comparison function. You learn a lot by doing things yourself.

Anyways, I did need the second if because, just like strcmp, if the user enters a space as the last character of their string, and the second string does not have that space, it still says they're the same.

This is not true. For example:

Code:

   char a[80] = "Tiger";
   char b[80] = "Tiger ";

   if (strcmp(a,b) == 0)
      cout << "Strings are the same." << endl;
   else
      cout << "Strings aren't the same." << endl;

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