Header inclusion question

**Victor Bazarov** · Jul 22 '05, 10:34 PM

Re: Header inclusion question

Johannes Bauer wrote:[color=blue]
> I've got a question concerning inclusion of .hpp files. Currently I'm
> including all needed header files in the .cpp file. This means all
> dependencies of the package and all dependencies of these dependencies
> and so on.
>
> This is quite ugly.
>
> A start of an "Example.cp p" file could look like this
>
> #include "ClassC.hpp " // Needed by ClassB
> #include "ClassB.hpp " // Needed by Example
> #include "Example.hp p"
>
> Now what I could do would include the dependencies of dependencies in
> the .hpp files and do a
>
> #ifndef EXAMPLE_H
> #define EXAMPLE_H
> ...
> #endif[/color]

What does this have to do with dependencies?
[color=blue]
> Yet I think this is quite ugly too...
>
> Are there other alternatives?[/color]

The Only Right Way is to include only the headers that are needed to
resolve symbols in _that_ module (whether it's a translation unit or
another header).

If your 'ClassB.hpp' needs 'ClassC.hpp', then 'ClassB.hpp' should include
it, not 'Example.cpp'. If your 'Example.hpp' needs 'ClassB.hpp', then it
itself should include 'ClassB.hpp'.

Now, it's a different story when we start talking _needing_ to include
anything. And you can reduce the includes by forward-declaring as much as
possible. For example, if your class definition only declares the use of
some class by a pointer or a reference, there is no need for the compiler
to know the other class' definition.

Victor

**Andre Kostur** · Jul 22 '05, 10:34 PM

Re: Header inclusion question

Johannes Bauer <dfnsonfsduifb@ gmx.de> wrote in news:rplh82xip5 .ln2
@snifftop.sniff domain:
[color=blue]
> Hi group,
>
> I've got a question concerning inclusion of .hpp files. Currently I'm
> including all needed header files in the .cpp file. This means all
> dependencies of the package and all dependencies of these dependencies
> and so on.
>
> This is quite ugly.
>
> A start of an "Example.cp p" file could look like this
>
> #include "ClassC.hpp " // Needed by ClassB
> #include "ClassB.hpp " // Needed by Example
> #include "Example.hp p"
>
> Now what I could do would include the dependencies of dependencies in
> the .hpp files and do a
>
> #ifndef EXAMPLE_H
> #define EXAMPLE_H
> ...
> #endif
>
> Yet I think this is quite ugly too...
>
> Are there other alternatives?[/color]

IMHO, each header file should be able to be compiled on its own. Each
header should also have its own include guards. So in your case, for
each of your header files I should be able to create a .cpp file in which
the only thing it does is #include that header file, that .cpp file
should compile.

So for your example I should be able to create an "Example.cp p" file with
one line in it:

#include "Example.hp p"

and I should be able to compile the Example.cpp file without any
problems. In your case that would mean

Example.cpp:

#include "Example.hp p"

Example.hpp:

#ifndef INC_EXAMPLE_HPP
#define INC_EXAMPLE_HPP

#include "ClassB.hpp "

void somefn(ClassB var);

#endif

ClassB.hpp:

#ifndef INC_CLASSB_HPP
#define INC_CLASSB_HPP

class ClassB
{
public:
void someotherfn(Cla ssA var);
};

#endif

ClassA.hpp:

#ifndef INC_CLASSA_HPP
#define INC_CLASSA_HPP

class ClassA
{
public:
void somethirdfn();
};

#endif

**E. Robert Tisdale** · Jul 22 '05, 10:34 PM

Re: Header inclusion question

Johannes Bauer wrote:
[color=blue]
> I've got a question concerning inclusion of .hpp files.
> Currently, I'm including all needed header files in the .cpp file.
> This means all dependencies of the package
> and all dependencies of these dependencies and so on.
>
>
>
> This is quite ugly.
>
> A start of an "Example.cp p" file could look like this
>
> #include "ClassC.hpp " // Needed by ClassB
> #include "ClassB.hpp " // Needed by Example
> #include "Example.hp p"
>
> Now what I could do would include the dependencies of dependencies in
> the .hpp files and do a
>
> #ifndef GUARD_EXAMPLE_H
> #define GUARD_EXAMPLE_H 1
> // contents of header file
> #endif//GUARD_EXAMPLE_H
>
> Yet I think this is quite ugly too...
>
> Are there other alternatives?[/color]

Your header files appear to be module interfaces.
Each such header file should be both

1. idempotent and
2. self-sufficient.

Use "guard" macros as shown above
to ensure that the contents of your header file
is parsed only once by the C preprocessor.

Each header file should include *all*
od the header files that it requires.
This means that, in this case,
the only header file that you need to include
in Example.cpp is Example.hpp

**Lawrence Troxler** · Jul 22 '05, 10:34 PM

Re: Header inclusion question

Andre Kostur <nntpspam@kostu r.net> wrote:

: IMHO, each header file should be able to be compiled on its own.

Yes.

: So for your example I should be able to create an "Example.cp p" file with
: one line in it:

: #include "Example.hp p"

: and I should be able to compile the Example.cpp file without any
: problems.

Why go through all this trouble? With good development tools, you should
be able to directly compile the header file.
There should be no need to create this "Example.cp p" just for testing purposes.

Of course, there are probably no "good development tools" in this context.
In a certain Microsoft Windows GUI C++ development environment, for
example, it doesn't work from the GUI - you can't simply open a header file
in the IDE editor and compile it.

Larry

**EventHelix.com** · Jul 22 '05, 10:34 PM

Re: Header inclusion question

Header file inclusion can be simplified by effective use of forward
declarations. See the following article:

http://www.eventhelix.com/RealtimeMa...dePatterns.htm

Deepa
--

Systems Engineering and Architecture Design Tool | EventStudio

http://www.EventHelix.com/EventStudio

Sequence diagram based systems engineering and architecture design tool. Built in support for alternative scenarios and multi-tier architectures.

EventStudio 2.5 - Generate sequence diagrams from plain text input

**EventHelix.com** · Jul 22 '05, 10:35 PM

Re: Header inclusion question

Header file inclusion can be simplified by effective use of forward
declarations. See the following article:

http://www.eventhelix.com/RealtimeMa...dePatterns.htm

Deepa
--

Systems Engineering and Architecture Design Tool | EventStudio

http://www.EventHelix.com/EventStudio

Sequence diagram based systems engineering and architecture design tool. Built in support for alternative scenarios and multi-tier architectures.

EventStudio 2.5 - Generate sequence diagrams from plain text input

Header inclusion question

Header inclusion question

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