Re: Reversing a String

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 21 Dec 2007 09:31:58 -0500

Message-ID:

<fkgiou$sah$1@news.datemas.de>

Barry Schwarz wrote:

On Tue, 18 Dec 2007 10:54:18 +1030, "Ron Francis"
<ronfrancis@adam.com.au> wrote:

I liked Giovanni's idea of doing it in place and thought I would try
to code it.

I would only pass the string I wanted to convert rather than trying
to assign memory within the function.
If you want a copy, you can copy the string first and send the copy
to the function.

void ReverseString(char *str){
   char *ptr1,*ptr2;
   char ch;
   int len, len2;

   len=strlen(str);
   if(!len)
       return;
   //len2 is used to step step half way into the string
   len2=len / 2;

   for(int i=0;i<len2;i++){
       //initially point to the first character
       ptr1=&str[i];
       //and point to the last character
       ptr2=&str[len-1-i];
       //swap the characters using ch as a temporary store
       ch=*ptr2;
       *ptr2=*ptr1;
       *ptr1=ch;

The pointers serve no purpose. You can move the characters directly
with
   ch = str[len-1-i];
   str[len-1-i] = str[i];
   str[i] = ch;

Or with
std::swap(str[len-1-i], str[i]);

}
}

Note that len-1 is needed because the array is 0 based.
&str[len] would point to a character beyond the string, possibly the
null character.

By definition of the strlen function, &str[len] cannot point beyond
the end of the string. If &str[len] does not point to the terminating
null character, then it is not a string.

V
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