precompiled headers question

  • Thread starter Thread starter Abubakar
  • Start date Start date
A

Abubakar

Hi,

I am writing some unmanaged c++ code that would need to be compiled in the
future using compilers other than vc++. I'm using the feature of vc++ "use
precompiled headers", is there going to be any problem if I compile this
code on other compilers? I'm asking this because when I use pch *some* of my
cpp files has following as there first line

#include "StdAfx.h"

but if I dont use pch, I have to change that to

#include "../StdAfx.h"

Regards,

Ab.
 
I am writing some unmanaged c++ code that would need to be compiled in the
future using compilers other than vc++. I'm using the feature of vc++ "use
precompiled headers", is there going to be any problem if I compile this
code on other compilers? I'm asking this because when I use pch *some* of
my
cpp files has following as there first line

#include "StdAfx.h"

but if I dont use pch, I have to change that to

#include "../StdAfx.h"
Click to expand...

Hi,

This will not be a problem. You can enable or disable the use of precompiled
headers in your project configuration properties. You don't have to change
anything to your sources at all.

Going to another compiler will not be a problem in that regard, but you have
to check whether you use microsoft specific features or not. you could /Za
to disable language extensions to insure that you only use ANSI.C++.

Btw GCC 4 also support precompiled headers I believe.

--

Kind regards,
Bruno van Dooren
(e-mail address removed)
Remove only "_nos_pam"
 
headers in your project configuration properties. You don't have to change
anything to your sources at all.
Click to expand...

then why do I have to change the "stdafx.h" to "../stdafx.h" when I'm not
using pch?

Should I delete this #include "stdafx.h" from the start of my *cpp* files
when NOT using pch?

Ab.
 
headers in your project configuration properties. You don't have to
then why do I have to change the "stdafx.h" to "../stdafx.h" when I'm not
using pch?
Click to expand...

You shouldn't have to. Just right click the file, select properties, go to
C++ ->precompiled headers.
there you can change the PCH usage.
You can also do this at project level.
Should I delete this #include "stdafx.h" from the start of my *cpp* files
when NOT using pch?
Click to expand...

No, because most times it actually contains other headers.
Also, if the project is configured to use pch, you will get a compiler error
when you don't include it.
Using or not using PCH is a setting. It should not affect your sources at
all.

It is a technique for speeding up compilation times. nothing more.


--

Kind regards,
Bruno van Dooren
(e-mail address removed)
Remove only "_nos_pam"
 
Abubakar said:
Hi,

I am writing some unmanaged c++ code that would need to be compiled in the
future using compilers other than vc++. I'm using the feature of vc++ "use
precompiled headers", is there going to be any problem if I compile this
code on other compilers? I'm asking this because when I use pch *some* of
my
cpp files has following as there first line

#include "StdAfx.h"

but if I dont use pch, I have to change that to

#include "../StdAfx.h"
Click to expand...

Then you have path problems in your project environment.

When you're compiling with PCH, the compiler completely ignores everything
in the file up through #include "stdafx.h". The fact that you have to
change the path when you don't use PCH to me indicates that the compiler
can't find your stdafx.h in any of the standard places.

What does the directory structure of your project look like? In particular,
where are stdafx.h and the file containing the #include in relation to one
another?

-cd
 
What does the directory structure of your project look like? In
particular,
where are stdafx.h and the file containing the #include in relation to one
Click to expand...

All my source files are not in the same folder. I have made extra folders to
contain source and headers. For example, there is a folder called Publish,
which contains headers and sources of publishing functionality. When I added
these files to my project as new items, they had there first line as
"#include "stdafx.h"". That was the time when my project settings had pch
enabled. Than at some point I changed project settings to not using pch,
after which when I compiled the project I started getting these errors that
there was no stdafx.h. But I knew that stdafx.h is at the root of the source
tree, so I just changed it to "#include "../stdafx.h"" and it compiled fine,
which also got me thinking why was it (lets say blockpublishing.cpp)
compiling before when it had no stdafx.h on its path. (my lack of cpp
knowledge).

I have other problems as well, related to header files includes. Like I have
a common.h file that has some utility functions and some global variables
that I intend to use at more than one place. Now I include common.h at one
file, lets say one.h and use its functions which works ok, and than at some
other place,lets say two.h, I include the common.h and compiler starts
giving me errors, while linking the source, saying that
"something__proc___here" is already defined in "something.obj". However if I
dont include common.h in two.h, the two.h has no idea of the things (global
functions and variables) that I write, which I assume will me visible to
two.h that are inside the common.h. Now the next thing I'm planning to do is
inlcude my common.h in stdafx.h and see what happens. Also will play with
#pragma once stuff which looks insteresting and I hope its not microsoft
specific.

The purpose I wrote this second para above is:
Having a C# background, I think I really need to read some really good and
detailed article on the problems that a dev can face while working on c++
projects having to do with #include. It would be great if you or anyone else
has some web links on this, or maybe discuss here.


Ab.
 
What does the directory structure of your project look like? In
particular,

All my source files are not in the same folder. I have made extra folders to
contain source and headers. For example, there is a folder called Publish,
which contains headers and sources of publishing functionality. When I added
these files to my project as new items, they had there first line as
"#include "stdafx.h"". That was the time when my project settings had pch
enabled. Than at some point I changed project settings to not using pch,
after which when I compiled the project I started getting these errors that
there was no stdafx.h. But I knew that stdafx.h is at the root of the source
tree, so I just changed it to "#include "../stdafx.h"" and it compiled fine,
which also got me thinking why was it (lets say blockpublishing.cpp)
compiling before when it had no stdafx.h on its path. (my lack of cpp
knowledge).
Click to expand...

That is because the compiler will look for the PCH instead of trying to load
the real include file.

if you separate include and source files you have to add additional include
directories in your project settings. otherwise you have to explicitly tell
the compiler where those files are (by using ../..) and that removes
flexibility from your project layout.
I have other problems as well, related to header files includes. Like I have
a common.h file that has some utility functions and some global variables
that I intend to use at more than one place. Now I include common.h at one
file, lets say one.h and use its functions which works ok, and than at some
other place,lets say two.h, I include the common.h and compiler starts
giving me errors, while linking the source, saying that
"something__proc___here" is already defined in "something.obj". However if I
dont include common.h in two.h, the two.h has no idea of the things (global
functions and variables) that I write, which I assume will me visible to
two.h that are inside the common.h. Now the next thing I'm planning to do is
Click to expand...

do it like this:
//common.h
extern int g_Global;
extern int MyFunction(void);

//common.cpp
#include "common.h"
int g_Global;
int MyFunction(void)
{
//...
}

that way there is only 1 definition, and you can use them by simply
including common.h
inlcude my common.h in stdafx.h and see what happens. Also will play with
#pragma once stuff which looks insteresting and I hope its not microsoft
specific.
Click to expand...

another thing you'll see often is this:

#ifndef __SOME_INCLUDE_GUARD__
#define__SOME_INCLUDE_GUARD__

//declarations here

#endif
The purpose I wrote this second para above is:
Having a C# background, I think I really need to read some really good and
detailed article on the problems that a dev can face while working on c++
projects having to do with #include. It would be great if you or anyone else
has some web links on this, or maybe discuss here.
Click to expand...

to find out if something is MSFT specific, find the topic in the MSDN help
collection. it is always mentioned if something is ANSI or microsoft specific.

www.codeproject.com is always a good place to start when looking for info.
if you are serious about C++ you should buy a good book. there are several.
my favorite is still 'the C++ programming language' by stroustrub
it can be a bit dull at times, but it is complete.

if you have specific questions you can always ask them here also.

--

Kind regards,
Bruno.
(e-mail address removed)
Remove only "_nos_pam"
 
Bruno van Dooren said:
That is because the compiler will look for the PCH instead of trying to load
the real include file.

if you separate include and source files you have to add additional include
directories in your project settings. otherwise you have to explicitly tell
the compiler where those files are (by using ../..) and that removes
flexibility from your project layout.
do is

do it like this:
//common.h
extern int g_Global;
extern int MyFunction(void);

//common.cpp
#include "common.h"
int g_Global;
int MyFunction(void)
{
//...
}

that way there is only 1 definition, and you can use them by simply
including common.h


another thing you'll see often is this:

#ifndef __SOME_INCLUDE_GUARD__
#define__SOME_INCLUDE_GUARD__

//declarations here

#endif


to find out if something is MSFT specific, find the topic in the MSDN help
collection. it is always mentioned if something is ANSI or microsoft specific.

www.codeproject.com is always a good place to start when looking for info.
if you are serious about C++ you should buy a good book. there are several.
my favorite is still 'the C++ programming language' by stroustrub
it can be a bit dull at times, but it is complete.

if you have specific questions you can always ask them here also.

--

Kind regards,
Bruno.
(e-mail address removed)
Remove only "_nos_pam"
Click to expand...
 
do it like this:
//common.h
extern int g_Global;
extern int MyFunction(void);
Click to expand...

This was very helpful.

Thanks for all other tips as well. My #include problems are settling slowly
n slowly :-)

Regards,

Abubakar.
 
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