C oddity?

Aaron_Adams · 04-11-2002, 02:16 AM

I don't understand the following.

If I were writing a program equivelent to strcat for instance:

Code:

void strcat(char *s1, char *s2)
{
    while(*s1++);
    while(*s1++ = *s2++);
}

The above, IMHO should work. Yet it does not. Although *s1++ = *s2++ works fine for the second while loop, *s1++ for the first while loop does not. You must instead write:

Code:

void strcat(char *s1, char *s2)
{
    while(*s1)
        *s1++;
    while(*s1++ = *s2++);
}

Can anyone explain to me why? I understand it really makes no speed difference or anything, I'm just boggled as to why it doesn't work.

Aaron_Adams · 04-21-2002, 09:41 PM

If anyone is interested in the solution to this, there was a respone on linuxnewbie.org

The solution is

Code:

void strcat(*char s1, *char s2)
{
    while(*++s1);
    while(*s1++ = *s2++);
}

The reason being is because the first while statement was testing for '/0', would find it but still increment past it, thus screwing up the testing of the next while statement. From what I understand anyways.

**paradox** · 04-22-2002, 03:34 PM

:'(

Had I seen this post I could have answered it. I hate pointers, I think I have had every friggin problem in the world with pointers, this being one of them. :-\

Pointers are a pain in the arse!

Aragorn