C / C++ / MFC

2-Apr-08 4:22

Does anyone here know a way of using the value of a constant class member in an #if condition.
What I'd like to do for example is :-

<br />
class CSomething<br />
{<br />
  public:<br />
<br />
  //...<br />
  enum<br />
  {<br />
    E_IsCool = 1;<br />
  };<br />
};<br />
<br />
//Then later conditional compilation based on E_IsCool<br />
<br />
#if (CSomething::E_IsCool)<br />
//Insert cool code here<br />
#else<br />
//Insert uncool code here<br />
#endif<br />
<br />

This may seem unnecessary when there is only one CSomething but I have several different ones, some cool some not and then a typedef is used to give one of them the name that is actually used. I'm trying to avoid peppering the classes with #defines and #undefs

Nothing is exactly what it seems but everything with seems can be unpicked.

Re: Mixed metaphor problem [modified]

Nemanja Trifunovic2-Apr-08 4:42

Nemanja Trifunovic

2-Apr-08 4:42

I think some template meataprogramming[^] would serve you better than the preprocessor #if

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utf8-cpp

Matthew Faithfull2-Apr-08 4:50

2-Apr-08 4:50

Yes it would normally and I've been thinking about using it. There is one small snag though. What if the conditional code is something like this:-

<br />
#if (CSomething::E_IsCool)<br />
#define _LONG_SUFFIX(_X) _X#L<br />
#else<br />
#define _LONG_SUFFIX(_X) _X<br />
#endif<br />

I can't find any way to pull in things like this that seem to have to be macros conditionally at the moment and I'm only really sold on going the template-mp route if I can do it all that way. Unsure | :~

Nothing is exactly what it seems but everything with seems can be unpicked.

modified on Wednesday, April 2, 2008 10:59 AM

CPallini2-Apr-08 4:50

CPallini

2-Apr-08 4:50

Matthew Faithfull wrote:
This may seem unnecessary when there is only one CSomething but I have several different ones, some cool some not and then a typedef is used to give one of them the name that is actually used

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

Matthew Faithfull2-Apr-08 5:06

2-Apr-08 5:06

I was trying to keep the example simple, obviously I failed Smile | :)

<br />
class CSomething<br />
{<br />
public:<br />
<br />
  //...<br />
  enum<br />
  {<br />
    E_IsCool = 1;<br />
  };<br />
};<br />
<br />
<br />
#ifdef USE_MYSOMETHING<br />
typedef CMySomething CSomething<br />
#else<br />
//Other CSomething alternatives<br />
#endif<br />
<br />
<br />
//Then later conditional compilation based on E_IsCool<br />
<br />
#if (CMySomething::E_IsCool)<br />
#define _LONG_SUFFIX(_X) _X#L<br />
#else<br />
//Insert uncool code here<br />
#define _LONG_SUFFIX(_X) _X<br />
#endif<br />
<br />

This is closer to what I'm really doing which is somewhat more complicated. It has to work on different compilers as that really is the point of this so any template tricks will need to be MSVC6 friendly

Nothing is exactly what it seems but everything with seems can be unpicked.

led mike2-Apr-08 5:10

2-Apr-08 5:10

Wow. So you don't know what a "pre" processor is in the context of a compiler?

led mike

Matthew Faithfull2-Apr-08 5:16

2-Apr-08 5:16

Yes Mike I do know and am not expecting the example code I posted to work. I need something functionally equivalent to what it would do if it did work, i.e. if the PRE-processor was C++ aware. If you're telling me there's no way to control conditional compilation using compile time constants then just come out and say so.

Nothing is exactly what it seems but everything with seems can be unpicked.

led mike2-Apr-08 5:31

2-Apr-08 5:31

Matthew Faithfull wrote:
Yes Mike I do know

What, then why have you asked this question? I mean if you know then you know so why ask the question? Wait, now I remember trying to have a logical discussion with you in the SoapBox, never mind.

led mike

Matthew Faithfull2-Apr-08 5:50

2-Apr-08 5:50

Yes, you didn't understand the use of a metaphor then and you clearly still don't.

Nothing is exactly what it seems but everything with seems can be unpicked.

led mike2-Apr-08 5:54

2-Apr-08 5:54

Metaphor this you f***ing idiot

led mike

CPallini2-Apr-08 5:18

CPallini

2-Apr-08 5:18

I see no alternatives to using define in your classes.
Smile | :)

BTW why cannot you use USE_MYSOMETHING to distinguish between suffixes?

Matthew Faithfull2-Apr-08 5:28

2-Apr-08 5:28

You may be right I was hoping someone would have a brainwave. Sigh | :sigh:

The reason I wouldn't use USE_MYSOMETHING is because it isn't really that simple, that would be the equivalent of one case in a page long block of #if #elif #endif code, not something I'd want to repeat in more than one place. I'm left with using that lump of code to #define yet another symbol e.g. USE_SUFFIXES and then using that. It's what everyone else does but I was hoping to improve on the state of the art Big Grin | :-D

Nothing is exactly what it seems but everything with seems can be unpicked.

led mike2-Apr-08 5:37

2-Apr-08 5:37

Matthew Faithfull wrote:
It's what everyone else does but I was hoping to improve on the state of the art

You should stick with learning the current state of the art before you decide to try and improve it. Roll eyes | :rolleyes:

led mike

Matthew Faithfull2-Apr-08 5:49

2-Apr-08 5:49

Where were you I wonder when I successfully ported Jaakko Järvi's tuple class to MSVC6, 9 months before the Boost developers managed it?
If you don't have anything useful to contribute you should stick to the Soapbox or better yet not post. Hmmm | :|

Nothing is exactly what it seems but everything with seems can be unpicked.

led mike2-Apr-08 5:53

2-Apr-08 5:53

Yeah try to prove you know what you are doing by citing some project you did, good one. To late, the cat's out of the bag now.

Matthew Faithfull wrote:
you should

What? I should what, take your advice? Laugh | :laugh:

When hell freezes over dude, when pigs fly, when bears sh*t in the woods, when, wait, well you get the idea.

led mike

Michael Dunn2-Apr-08 10:18

Michael Dunn

2-Apr-08 10:18

The preprocessor doesn't work like that. It just sees text and has no knowledge of the value of E_IsCool. You'll need to do something like (just the snippets here):

#define E_IS_COOL_VALUE 1

enum { E_IsCool = E_IS_COOL_VALUE };

#if E_IS_COOL_VALUE != 0

--Mike--
Visual C++ MVP Cool | :cool:

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Matthew Faithfull2-Apr-08 12:16

check file opened or not?

2-Apr-08 12:16

Yes, I realize the preprocessor isn't going to cut it. I wondered if there was any other mechanism to get the compiler to conditionally ignore/notice chunks of code with a similar effect to the preprocessor but during actual compilation. For the moment I've worked round it but in the longer run that's going to mean defining things in multiple places which is not exactly splendid. Anyway you can see how it works out as this is part of what will almost certainly be my next article, the Compiler abstraction library I ranted at Marc Clifton about nearly a year ago, expect it any time in the next 12 months Laugh | :laugh:

Thanks.

Nothing is exactly what it seems but everything with seems can be unpicked.

George_George2-Apr-08 3:55

George_George

2-Apr-08 3:55

Hello everyone,

On Windows platform, which API could be used to check whether a file is opened (either by other thread or process or even the same thread) or not?

C++ is fine.

thanks in advance,
George

David Crow2-Apr-08 4:16

David Crow

2-Apr-08 4:16

One such way is with a device driver (like the one created for use with FileMon and Handle).

You can also check out NetFileEnum().

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

George_George2-Apr-08 20:40

George_George

2-Apr-08 20:40

Hi DavidCrow,

After reading the MSDN document for NetFileEnum, I am confused. The description is,

--------------------
The NetFileEnum function returns information about some or all open files on a server, depending on the parameters specified.
--------------------

Server means? I just want to find all the used (open) files on the local machine. Any ideas or comments?

regards,
George

David Crow3-Apr-08 3:06

David Crow

3-Apr-08 3:06

George_George wrote:
Server means? I just want to find all the used (open) files on the local machine. Any ideas or comments?

servername
[in] Pointer to a Unicode (Windows NT/2000/XP) or ANSI (Windows 95/98/Me) string specifying the name of the remote server on which the function is to execute. The string must begin with \\. If this parameter is NULL, the local computer is used.

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne