Inclusion guards

[Dave]

Hello all,

To protect against multiple inclusions, it is standard practice to enclose
the contents of a header file in a construct like this:

#ifndef FOO_INCLUDED
#define FOO_INCLUDED
....
#endif
I need to automate the creation of the guard macro name, perhaps by doing
something like this:

#define MACRO_NAME_CREA TOR(TEXT) TEXT##_INCLUDED

#ifndef MACRO_NAME_CREA TOR(__FILE__)
#define MACRO_NAME_CREA TOR(__FILE__)
....
#endif
However, this does not work. Can anybody offer a technique that will
accomplish what is intended above?

Thanks,
Dave

[E. Robert Tisdale]

Dave wrote:

To protect against multiple inclusions,
it is standard practice to enclose the contents of a header file
in a construct like this:

#ifndef FOO_INCLUDED
#define FOO_INCLUDED 1
// ...
#endif//FOO_INCLUDED
I need to automate the creation of the guard macro name, perhaps by doing
something like this:

#define MACRO_NAME_CREA TOR(TEXT) TEXT##_INCLUDED

#ifndef MACRO_NAME_CREA TOR(__FILE__)
#define MACRO_NAME_CREA TOR(__FILE__)
...
#endif

However, this does not work. Can anybody offer a technique that will
accomplish what is intended above?

No.

Notice that your header file isn't idempotent
because it includes the MACRO_NAME_CREA TOR definition
before it checks to see if it is defined.

[JH Trauntvein]

Dave wrote:

Hello all,

To protect against multiple inclusions, it is standard practice to enclose the contents of a header file in a construct like this:

#ifndef FOO_INCLUDED
#define FOO_INCLUDED
...
#endif
I need to automate the creation of the guard macro name, perhaps by doing something like this:

#define MACRO_NAME_CREA TOR(TEXT) TEXT##_INCLUDED

#ifndef MACRO_NAME_CREA TOR(__FILE__)
#define MACRO_NAME_CREA TOR(__FILE__)
...
#endif
However, this does not work. Can anybody offer a technique that will
accomplish what is intended above?

Thanks,
Dave

You might want to look into a compiler specific feature like "pragma
once" used with visual c++. GCC also has a similar feature but the
memory of how to invoke it escapes me.

[JH Trauntvein]

Dave wrote:

Hello all,

To protect against multiple inclusions, it is standard practice to enclose the contents of a header file in a construct like this:

#ifndef FOO_INCLUDED
#define FOO_INCLUDED
...
#endif
I need to automate the creation of the guard macro name, perhaps by doing something like this:

#define MACRO_NAME_CREA TOR(TEXT) TEXT##_INCLUDED

#ifndef MACRO_NAME_CREA TOR(__FILE__)
#define MACRO_NAME_CREA TOR(__FILE__)
...
#endif
However, this does not work. Can anybody offer a technique that will
accomplish what is intended above?

Thanks,
Dave

You might want to look into a compiler specific feature like "pragma
once" used with visual c++. GCC also has a similar feature but the
memory of how to invoke it escapes me.

[Sebastian Redl]

JH Trauntvein wrote:

Dave wrote:
You might want to look into a compiler specific feature like "pragma
once" used with visual c++. GCC also has a similar feature but the
memory of how to invoke it escapes me.

The GCC feature recognizes an inclusion guard and marks the file. Having
"fancy" inclusion guards thus makes compiling under GCC less efficient.

I don't see the necessity for generating inclusion guards by macros. The
name Trauntvein used for his hypothetical macro is already longer than most
inclusion guards I use. I have this simple scheme:

_<file name using _ instead of .>_SR_H_

The SR_H marks the file as a header created by me. It takes me very little
time to write this guard, especially as
#ifndef
and
#define
are the same number of characters, so copy&paste of the macro name to the
line below is very fast.
--
Sebastian Redl

[Victor Bazarov]

Sebastian Redl wrote:

JH Trauntvein wrote:

Dave wrote:
You might want to look into a compiler specific feature like "pragma
once" used with visual c++. GCC also has a similar feature but the
memory of how to invoke it escapes me.

The GCC feature recognizes an inclusion guard and marks the file. Having
"fancy" inclusion guards thus makes compiling under GCC less efficient.

I don't see the necessity for generating inclusion guards by macros. The
name Trauntvein used for his hypothetical macro is already longer than most
inclusion guards I use. I have this simple scheme:

_<file name using _ instead of .>_SR_H_

If your file name begins with a capital letter, the name formed here would
be reserved and you'd be in violation of the Standard rules about naming.
What's that desire to begin everything with an underscore, anyway?

How often do you really have to read those once they're written? Their
position in the file is not going to change. No other files are supposed
to define them, or use them, for that matter.

Making them unique throughout the project is not such a bad idea. Headers
generated by Microsoft Visual Studio contain some long macro names made up
by the same mechanism as their GUID (see OLE) generator, which definitely
prevents them from being the same in two separate files. You may consider
it overkill but think about it. If you worry about the inclusion guards'
being specific to the file, what if you have two files with the same name
in the same project. They may never be included into the same file at the
beginning of the project, but projects grow, and headers include headers,
so you may end up with _data_h_SR_H_ defined in one "data.h" and then also
_data_h_SR_H_ in the other "data.h" elsewhere...

Anyway, I didn't mean to barge in like that, just dropping my $0.02 in...
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