totse.com | anyone here good with C? quick question

opersono · #1 2007-04-08, 00:45

okay, so i'm stumped by this question even though I've done java database programming for years, and I know a fair amount of C++.

here is goes. what does this function do in C?

By the way, the two parameters represent char arrays (strings, with a capacity of 80, if that matters).
The user is prompted to input two strings, which are then passed to this function. Here it goes:

Void blah (char *s1, const char *s2)
{

while ( s1 != ‘\10’) /* while it doesn’t equal 10 */
{
s1++;
}

for (; *s1 = *s2; s1++, s2++)
{
; /* YEA, this is an empty statement */

}

} /* end of blah function */

I’ve never heard of incrementing a char array

Please help.

jsaxton14 · #2 2007-04-08, 01:08

This is an example of pointer arithmetic. s1 is just a pointer to s1[0]. Incrementing s1 simply increases the address of s1, so it now points to s1[1] instead.

What is '\10'?

opersono · #3 2007-04-08, 01:11

oh shit, i meant \0, as in NULL.

so after this function, what would happen if i were to print the value of s1?

jsaxton14 · #4 2007-04-08, 01:16

After a bit of tinkering, I figured out that '\x' is a valid character. x is simply an octal representation of an ascii character. It turns out '\10' is backspace.

http://www.asciitable.com/

jsaxton14 · #5 2007-04-08, 01:21

The output of this code is dependent upon the values of *s1 and *s2. If *s1="foo\0barbaz" and *s2="baz", I think what would happen is that a printf("%s\n", s1) would print "rbaz" but I'm not 100% positive.

Let me code up a little test program.

opersono · #6 2007-04-08, 01:23

please do. that would be of help

jsaxton14 · #7 2007-04-08, 01:33

I'm an idiot. This is just a version of strcpy(), basically. For some reason I read "*s1 = *s2" as "*s1 == *s2".

For some reason it's not compiling properly on my computer (it keeps segfaulting). I have my own homework to do, so I'm going to start working on that now.

Good luck.

carpal · #8 2007-04-08, 03:52

for (; *s1 = *s2; s1++, s2++)
{
; /* YEA, this is an empty statement */

}

I maybe wrong but isn't this an infinite loop?

opersono · #9 2007-04-08, 05:50

i think it just appears that way, but i could just be saying that because the For loops in C could be very different that the For loops in c++ and java.

bump though, i could really use an answer.

jsaxton14 · #10 2007-04-08, 16:02

Code:

#include<stdio.h>



int main() {

        int foo[4] = {0,1,2,5};

        int bar[2] = {6,9};

        int i;

        for(i=0;foo[i]=bar[i];i++) {

                printf("%i\n", i);

        }

        return 0;

}

That code results in an infinite loop.

So I was wrong, it turns out that your code just results in an infinite loop. It is not a modified version of strcpy() like I initially thought.

Good luck.