Question in terms of design. Where to put "#include"?

[Goran]

Hi all,

this is just a "design" question.

I'm unsure where to put my "#includes".

Should I put it directly into headerfiles? Or into sourcefiles with a
forward type declaration in headerfiles?

And if forward type declarations in headerfiles are used... why can't
I do something like...

class string;

and include string in the source file?

Thanks

Goran

[Bo Persson]

Goran wrote:
:: Hi all,
::
:: this is just a "design" question.
::
:: I'm unsure where to put my "#includes".
::
:: Should I put it directly into headerfiles? Or into sourcefiles
:: with a forward type declaration in headerfiles?

It depends on how much of a class you really use in the header.

To form a pointer or a reference, a declarations is enough. If you
call a member function, for example, you need the full definition.

::
:: And if forward type declarations in headerfiles are used... why
:: can't I do something like...
::
:: class string;
::
:: and include string in the source file?

Becase string isn't really a class, but a typedef for a template.
Bo Persson

[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

On 2007-09-03 18:06, Goran wrote:

Hi all,

this is just a "design" question.

I'm unsure where to put my "#includes".

Should I put it directly into headerfiles? Or into sourcefiles with a
forward type declaration in headerfiles?

Using forward declarations if you can is a good idea.

And if forward type declarations in headerfiles are used... why can't
I do something like...

class string;

and include string in the source file?

You can, sometimes. It depends on how you are using strings in your
header, for some things the compiler need to know more about the type
and then a forward declaration is not enough. As long as you only use
references or pointers to string then you should be fine.

--
Erik Wikström

[BobR]

BobR wrote in message...

>
// --- Guts.h ---
std::cout<<"Hello World, from Guts.h"<<std::endl;
#define BLAHBLAH cout<<"Hello World, from Guts.h"<<std::endl;

Oops, that should be:
#define BLAHBLAH std::cout<<"Hello World, from Guts.h"<<std::endl;

[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

On 2007-09-03 23:47, Jorgen Grahn wrote:

On Mon, 03 Sep 2007 09:06:48 -0700, Goran <po**********@gmail.comwrote:

>Hi all,

this is just a "design" question.

I'm unsure where to put my "#includes".

Should I put it directly into headerfiles? Or into sourcefiles with a
forward type declaration in headerfiles?

One common guideline (which some people disagree with) is that if you
have a header file foo.h, a file which just contains

#include "foo.h"

should compile. I.e., foo.h should include everything it needs to
compile (but not too much more).

>And if forward type declarations in headerfiles are used... why can't
I do something like...

class string;

and include string in the source file?

You /can/ do that, much of the time. There are rules for when you can
and when you cannot. If you're talking about std::string, it won't
work, because ... well, I guess std::string being a typedef is one
reason?

It should be possible, the problem is that it is a parametrised type, so
you have to include all the template parameters in the forward
declaration, which would require a forward declaration of char_traits
too if I am not mistaken.

--
Erik Wikström

[Pete Becker]

On 2007-09-03 18:24:12 -0400, Erik Wikström <Er***********@telia.comsaid:

On 2007-09-03 23:47, Jorgen Grahn wrote:

>>
You /can/ do that, much of the time. There are rules for when you can
and when you cannot. If you're talking about std::string, it won't
work, because ... well, I guess std::string being a typedef is one
reason?

It should be possible, the problem is that it is a parametrised type,
so you have to include all the template parameters in the forward
declaration, which would require a forward declaration of char_traits
too if I am not mistaken.

Hypothetically, maybe. But the standard is explicit: if you use the
name without including the standard header, the behavior is undefined.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[James Kanze]

On Sep 3, 7:05 pm, Erik Wikström <[e-mail]:

On 2007-09-03 18:06, Goran wrote:

[...]

And if forward type declarations in headerfiles are used... why can't
I do something like...

class string;

and include string in the source file?

You can, sometimes. It depends on how you are using strings in your
header, for some things the compiler need to know more about the type
and then a forward declaration is not enough. As long as you only use
references or pointers to string then you should be fine.

No. As others have pointed out, std::string is not a class, so
the forward declaration doesn't work.

--
James Kanze (GABI Software) email:[e-mail]
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