[turtleC++]

Hi,

I try to reverse string but the function ReverseString() does not work using the second call. Why is that?

void ReverseString(char *c)
{
	int length = strlen(c);

	char *front = c;
	char *end = c + length - 1;
	char ftemp = NULL;
	char etemp = NULL;
	
	while (end >= front)
	{
		ftemp = *front;
		etemp = *end;
		*front = etemp;
		*end = ftemp;
		front++;
		end--;

	}

	cout<<c;

}

int _tmain(int argc, _TCHAR* argv[])
{
	char sentence[] = "hello world";

	ReverseString(sentence, reverseStr2);//first call and this works
	ReverseString("hello world", reverseStr2);//second call, but does not work

	return 0;
}

[jimblumberg]

Please provide a complete compilable program that illustrates your problem, and indicate whether this is a C or C++ program.

Jim

[turtleC++]

the program is for C++.

[jimblumberg]

Post the smallest complete program that illustrates your problem.

Jim

[sepp2k]

With the code you've given, neither of the two calls will work because you've defined ReverseString to take one argument, but you're calling it with two. Also reverseStr2 isn't defined or declared anywhere.

That said, your problem most likely is that you can't mutate string literals. That's undefined behavior (and will cause a segfault or equivalent on the majority of platforms).

[turtleC++]

Opp sorry. It was meant to have one argument. So it will be like this.

01      void ReverseString(char *c)
02	{
03	    int length = strlen(c);
04	 
05	    char *front = c;
06	    char *end = c + length - 1;
07	    char ftemp = NULL;
08	    char etemp = NULL;
09	     
10	    while (end >= front)
11	    {
12	        ftemp = *front;
13	        etemp = *end;
14	        *front = etemp;
15	        *end = ftemp;
16	        front++;
17	        end--;
18	 
19	    }
20	 
21	    cout<<c;
22	 
23	}
24	 
25	int _tmain(int argc, _TCHAR* argv[])
26	{
27	    char sentence[] = "hello world";
28	 
29	    ReverseString(sentence);//first call and this works
30	    ReverseString("hello world");//second call, but does not work
31	 
32	    return 0;
33	}

This post has been edited by turtleC++: 29 March 2012 - 06:13 PM

[David W]

As well as noting what Sepp2k said above, you may want to study up on 'read-only' memory.

[r.stiltskin]

You can do this

ReverseString("hello world", reverseStr2);

if you rewrite your function to take 2 arguments. The second argument should be an empty array in which the function can store the result. Then it won't matter whether the original string is an array or a string literal.

This post has been edited by r.stiltskin: 30 March 2012 - 06:39 AM

[turtleC++]

David W, on 30 March 2012 - 04:25 AM, said:

As well as noting what Sepp2k said above, you may want to study up on 'read-only' memory.

thanks, I will do that.

r.stiltskin, on 30 March 2012 - 07:38 AM, said:

You can do this

ReverseString("hello world", reverseStr2);

if you rewrite your function to take 2 arguments. The second argument should be an empty array in which the function can store the result. Then it won't matter whether the original string is an array or a string literal.

earlier it worked with second argument, but I took one out but since I didn't know about read-only like previous posts mentioned. So i will read on that. thanks.

[David W]

Hint:

You may want to contrast ...

char test1[] = "0123456789";

with ...

char* test2 ="abcdefghij";

where you would need to first copy test2 into a 'buffer' to be able to reverse that copied string in that buffer ...