Question

I am trying to create a non-recursive method to swap a c-style string. It throws an exception in the Swap method. Could not figure out the problem.

void Swap(char *a, char* b)
{
    char temp;
    temp = *a;
    *a = *b;
    *b = temp;
}
void Reverse_String(char * str, int length)
{
    for(int i=0 ; i <= length/2; i++)  //do till the middle
    {
        Swap(str+i, str+length - i);

    }

}

EDIT: I know there are fancier ways to do this. But since I’m learning, would like to know the problem with the code.

Answer 1

It throws an exception in the Swap method. Could not figure out the problem.

No it doesn’t. Creating a temporary character and assigning characters can not possibly throw an exception. You might have an access violation, though, if your pointers don’t point to blocks of memory you own.

The Reverse_String() function looks OK, assuming str points to at least length bytes of writable memory. There’s not enough context in your question to extrapolate past that. I suspect you are passing invalid parameters. You’ll need to show how you call Reverse_String() for us to determine if the call is valid or not.

If you are writing something like this:

char * str = "Foo";
Reverse_String(str, 3);
printf("Reversed: '%s'.\n", str);

Then you will definitely get an access violation, because str points to read-only memory. Try the following syntax instead:

char str[] = "Foo";
Reverse_String(str, 3);
printf("Reversed: '%s'.\n", str);

This will actually make a copy of the "Foo" string into a local buffer you can overwrite.