Question about header conventions

[iw0XoG1T]

I have a question about headers. I read the article about headers from this website and it recommended a method to keep from including headers twice. After reading the article it occurred to me that I have never had a problem with headers. So I took a look at my include file and found that all the headers I use regularly are wrapped.

But I noticed this convention:

#ifndef _GLIBCXX_VECTOR
#define _GLIBCXX_VECTOR 1

#pragma GCC system_header

// removed this section

#endif /* _GLIBCXX_VECTOR */ 

What does the "1" in

#define _GLIBCXX_VECTOR 1

mean and why is it used?

[Bazzy]

#define _GLIBCXX_VECTOR 1
defines _GLIBCXX_VECTOR as a preprocessor constant with value 1,
#define _GLIBCXX_VECTOR
would be the same but without any value
see http://www.cplusplus.com/doc/tutorial/preprocessor/

[iw0XoG1T]

I guess I should have been more clear; is there a good reason for assigning the value of 1, and more importantly is this something I should be doing?

[Duthomhas]

Not necessarily. It is a convention used by the GCC. I do not know whether the value 1 is significant to the GCC or not, but it could be.

However, your headers should typically be of the form:

/* filename.hpp
 * product name/short description
 * copyright
 * license
 */

#pragma once
#ifndef UNIQUE_ID_FILENAME_HPP
#define UNIQUE_ID_FILENAME_HPP

#include <stuff>
#include <morestuff>

#include "etc"

namespace my_namespace
  {
  types and typedefs
  external constant declarations
  function prototypes
  etc
  }

#endif 

Hope this helps.

[iw0XoG1T]

Thank you for the example--yes it does help.