Question on pointers?

**robasc** · 12-23-2005

Hello everyone, I am in my first semester on C++ and I am wondering if someone could clarify my understanding of pointers.

Are pointers used sort of the same way as global variables.
In other words can I use a pointer just like I use a global variable in my program?

**Ancient Dragon** · 12-23-2005

yes, but they can be used like any other variable, global or not. Just make sure you initialize the pointer to something before you attempt to use it. Many people, including old-timers, make that mistake and wonder why their program crashes.

**robasc** · 12-23-2005

Thanks Dragon for your help on pointers, It's good to have help in understanding programming.
Much appreciated!

**LuckY** · 12-23-2005

Check out my "What's Up With Pointers?" tutorial. Quite a few people have found it very helpful.

Good luck.

**dwks** · 12-23-2005

Hey LuckY:

int kb = 1024;
int *ptr = kb;// Compile Error!

You might get a warning.

If we're posting tutorials . . . .

Prelude's Brain Vomit: http://eternallyconfuzzled.com/tuts/pointers.html
cprogramming.com's tutorial: http://www.cprogramming.com/tutorial.html
first on the list from google: http://cplus.about.com/od/beginnerct.../aa010502a.htm

**robasc** · 12-23-2005

If I am correct dwks would be

Code:

int kb = 1024;
int *ptr_kb = &kb;// correction

This would set the memory location of kb to *prt_kb

by the way excellent tutorial lucky!

**robasc** · 12-23-2005

Here are some ways I am learning how pointers work.

Code:

#include <iostream.h>

int main()
{
	    int count, temp;               // initialize variables

		int *count_ptr, *temp_ptr;     // initialize pointer variables

	count_ptr = &count;                // assign address count to ptr.

	temp_ptr = &temp;                  // assign temp to ptr.
	
/*  I noticed in the output below that the address of variable (count) is the same address as 
    variable pointer (count_ptr). */
		
    
	
	cout << "\n\n the address of count is  " << &count << "\n\n";
	
	cout <<"\n the address of count_ptr is  " << count_ptr <<"\n\n";
	
	
	{
		cout <<"_________________________________________________\n\n";

/* Here I am learning the understanding of pointers and the inderection operators
the inderection operator is (*). In conclusion, this pairing of the pointer variable and inderection
operator gives us a way to access directly variables that would otherwise be off limits to us.
(THIS IS IMPORTANT!!!). */

		int count = 4;                    

		int *count_ptr;

		count_ptr = &count;                        // assign address of count to ptr.
		 
		int m;

		m = *count_ptr;                            // assign count pointer to m which will equal to 4.

         cout << "hello *count_ptr = " << *count_ptr <<"\n\n";  // displays the value of 4.

		 cout << " m = count_ptr,  see!  " << m <<"\n\n";       //  here m also displays the value of 4.
	}       

	return 0;
}

**kermit** · 12-23-2005

Good to see you are working hard to learn. A couple of things you will want to consider:

Code:

#include <iostream.h>

You will want to use <iostream> in favour of <iostream.h>, something like this:

Code:

#include <iostream>

You should pay attention to namespace:

Code:

cout << "hello *....

You could do a number of things, like this:

Code:

std::cout << "hello *....

or this:

Code:

#include <iostream>

using std::cout;

int main()
{
   // rest of code

   return 0;

}

or even this: (though this last example is not necessarily the best idea, as it defeats the purpose of hiding functions within a namespace) You can read more about the subject here.

[code]
#include <iostream>

using namespace std;

int main()
{

// rest of code

return 0;
}

The other thing is a clarification on your notes:

Code:

int *count_ptr, *temp_ptr;     // initialize pointer variables

At that line you are only declaring the variables. You initialise them a little later when you assign a value to them here:

Code:

count_ptr = &count;                // initialise count_ptr with address of count.

temp_ptr = &temp;                  // initialise temp_ptr with address of temp.

Of course you have no doubt read that it is very important to make sure you initialise your pointer variables before you try to use them anywhere.

**robasc** · 12-23-2005

Thanks for the pointers on clarity I see my mistake there.

I must remember that you declare variables then initialize them.

I also noticed that you mentioned <iostream>.

Code:

#include <iostream>

int main(argc, char, *argv[])
{
  std :: cout << "hello";
 
 system ("pause");
  return EXIT SUCESS;
}

I use this in bloodshed compiler.

You must be using dev c++....?

I am using visual c++ on this code. Is it possible to use <iostream> in visual c++ because I tried it and it did'nt work?
In which I might add bloodshed is much better. This visual c++ just came with my book Titled "C++ Programming Today".

Thanks for the pointers!

**dwks** · 12-24-2005

Since you're using system(), you'll need to include <cstdlib> as well.

**dwks** · 12-24-2005

Originally Posted by robasc

If I am correct dwks would be

Code:

int kb = 1024;
int *ptr_kb = &kb;// correction

This would set the memory location of kb to *prt_kb

by the way excellent tutorial lucky!

Yes, that's the corrected code. But my point was simply that LuckY's code might not produce an error -- on my compiler it generates a warning.

**robasc** · 12-24-2005

I found it to work this way.
this is very interesting!

May I ask the importance of using <iostream> rather than <iostream.h>
Thanks!

Code:

#include <iostream>

using std::cout;

int main()

{
  std :: cout << "hello";

  return 0;
 
}

**robasc** · 12-24-2005

I got namespace to work now.

Code:

#include <iostream>

using namespace std;

int main()

{
  std :: cout << "hello";

  return 0;
 
}

I read the discussion above about namespace. I am not sure I understood all of it yet but I am going to read it again.

**dwks** · 12-24-2005

When you have using std::cout; or (ugh) using namespace std;, you can drop the std:: from couts. That's the whole point. If you're just going to leave the std:: in then you don't need anything special.

Code:

#include <iostream>

int main(void) {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}

or

Code:

#include <iostream>
using std::cout;
using std::endl;

int main(void) {
    cout << "Hello, World!" << endl;
    return 0;
}

or (as I said, ugh)

Code:

#include <iostream>
using namespace std;

int main(void) {
    cout << "Hello, World!" << endl;
    return 0;
}

**Daved** · 12-24-2005

>> May I ask the importance of using <iostream> rather than <iostream.h>

Because <iostream.h> is old and non-standard. That means that new compilers that follow standard C++ don't have to make it work. In fact, some already don't allow code with <iostream.h> to compile (including Visual C++ 7.1 and 8.0).

The <iostream> version is the newer version that was part of the standard in 1998. All your new code should use it even if your compiler still works with the older version so that if and when you move to a newer compiler, you don't have to change your code.

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