C / C++ / MFC

22-Nov-07 21:46

Anyway, the following one compiles:

#define PREFIX(x) _T("FOO") _T(#x)


int main()
{
  const TCHAR* SecondArray [2] = {PREFIX(FILE1), PREFIX(FILE2)};

  const TCHAR* p = NULL;
  p = SecondArray [0];
  p = SecondArray [1];
}

Be careful: copy exactly as it stands

Big Grin | :-D

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.

jhwurmbach22-Nov-07 21:58

22-Nov-07 21:58

Sure? I mean, nesting macros? Is that version-dependent?

No, it is not:
"...the formal parameter is immediately replaced by the unexpanded actual argument. Macro expansion is not performed on the argument prior to replacement."

Looks like your macro will expand to nonsense...;P
_T("FOO") _T(FILE1)

Let's think the unthinkable, let's do the undoable, let's prepare to grapple with the ineffable itself, and see if we may not eff it after all.
Douglas Adams, "Dirk Gently's Holistic Detective Agency"

George_George22-Nov-07 22:07

22-Nov-07 22:07

Hi jhwurmbach,

I do not quite understand your points. The code works in my Visual Studio 2005 environment. Could you show some pseudo code to express your ideas please?

regards,
George

CPallini22-Nov-07 22:11

22-Nov-07 22:11

Report of the macro expansion on my system:

const TCHAR* SecondArray [2] = {L"FOO" L"FILE1", L"FOO" L"FILE2"};

Then compiler string concatenation makes the trick.
Smile | :)

BTW it was only an academic question, since the search-and-replace tool of his favourite editor can do it painless.
Big Grin | :-D

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.

George_George22-Nov-07 22:04

22-Nov-07 22:04

Thanks CPallini,

regards,
George

jhwurmbach21-Nov-07 21:09

21-Nov-07 21:09

Macro?
Macros are expanded before the compiler runs. It doesn't even get to see the unexpanded macro.

So, when you know the "FILEn" and the FOO-part at compile time, why don't you #define the strings as "FOOFILEn" in the first place?
If you don't know the filename or the prefix at compiletime (i.e. you only get it at runtime) there is not much a macro can do for you.

George_George21-Nov-07 21:19

21-Nov-07 21:19

Thanks jhwurmbach,

I am just thinking that defining N macros is somewhat stupid. Smile | :)

Like,

#define NEWFILE1 "FOOFILE1"
...
#define NEWFILEN "FOOFILEN"

My situation is, I have some legacy code, which is an array -- very long, and all the file names are constant values. And to save my time of typing, I want to find some smarter ways to add prefix to all file names in the aray.

Any good ideas?

regards,
George

jhwurmbach21-Nov-07 21:32

21-Nov-07 21:32

George_George wrote:
My situation is, I have some legacy code, which is an array [...] I want to find some smarter ways to add prefix to all file names in the aray.

If you already have the filenames in an array of strings, then you can loop over the contents of the array and prepend your prefix to any one of them.

George_George21-Nov-07 21:50

21-Nov-07 21:50

Thanks jhwurmbach,

You mean using something like strcat to calculate the string at runtime? I think if we could determine the values at compile time (this is why I am asking people here to see whether we could use MACRO or something to determine the string values at compile time), the performance of runtime will be better.

regards,
George

jhwurmbach21-Nov-07 21:55

21-Nov-07 21:55

George_George wrote:
if we could determine the values at compile time the performance of runtime will be better.

So, you have some code-file where a long, long list of strings is added into an array?
Or do you read some sort of text file at startup?
Sorry, I can only give vague suggestions, but you are not providing enough information.
You have a fixed-size array of TCHARs.
When is this array filled?
From where is it filled?
How often is is accessed? At different code locations?

George_George21-Nov-07 23:56

21-Nov-07 23:56

Thanks jhwurmbach,

Here is some pseudo code, it is appreciated if you could share some ideas. Let me know if you need any further information.

<br />
#define PREFIX "FOO"<br />
<br />
int main()<br />
{<br />
	TCHAR array_before [5][256] = {_T("FILE1"), _T("FILE2"), _T("FILE3"), _T("FILE4"), _T("FILE5")};<br />
	// I want to make a new array like<br />
	// ("FOOFILE1"), _T("FOOFILE2"), _T("FOOFILE3"), _T("FOOFILE4"), _T("FOOFILE5")<br />
<br />
	// current implementation, strcat PREFIX + rray_before [i]<br />
<br />
	// iterate array in the followng<br />
<br />
	// array_before [0], array_before [1], <br />
}<br />
<br />
<br />
regards,<br />
George

jhwurmbach22-Nov-07 0:41

22-Nov-07 0:41

As CPallini and toxcct suggested, search&replace in the Editor or using Macro-Stringconcatenation if you are suspicious that the prefix might change in the future is probably the way to go.

Or loading the array content from a data-file at runtime, prefixing on the fly.

George_George22-Nov-07 1:27

22-Nov-07 1:27

Hi jhwurmbach,

For your idea,

> Or loading the array content from a data-file at runtime, prefixing on the fly.

You mean using strcat or something similar?

I have tried to use ##, but the code does not compile.

<br />
#define PREFIX(x) _T("FOO")##x<br />
<br />
int main()<br />
{<br />
<br />
	const TCHAR* SecondArray [2] = {_T("FILE1"), _T("FILE2")};<br />
<br />
	TCHAR* p = NULL;<br />
	p = PREFIX(SecondArray [0]);<br />
	p = PREFIX(SecondArray [1]);<br />
<br />
<br />
	return 0;<br />
}<br />

Error information,

main.c(11) : error C2146: syntax error : missing ';' before identifier 'SecondArray'
main.c(12) : error C2146: syntax error : missing ';' before identifier 'SecondArray'

regards,
George

Jonathan [Darka]21-Nov-07 21:41

Jonathan [Darka]

21-Nov-07 21:41

Macros are evil, try using an STL container and use foreach() or something similar to process the containers items and prepend "FOO" to each item.

Jonathan Wilkes
Darka[Xanya.net]

CPallini21-Nov-07 21:51

21-Nov-07 21:51

Jonathan [Darka] wrote:
Macros are evil

No.

(Provided you know what are you doing).

Smile | :)

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.

George_George21-Nov-07 21:52

21-Nov-07 21:52

Thanks for your advice, Darka!

I think your solution will calculate the string at runtime? I think if we could determine the values at compile time (this is why I am asking people here to see whether we could use MACRO or something to determine the string values at compile time), the performance of runtime will be better.

regards,
George

toxcct21-Nov-07 21:58

toxcct

21-Nov-07 21:58

#define FOOPREFIX(x) "FOO"##x

but i strongly advise against using such things

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CPallini21-Nov-07 22:32

21-Nov-07 22:32

Oh, such things are used here and there by mummy MS itself.
Big Grin | :-D

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.

toxcct21-Nov-07 22:35

toxcct

21-Nov-07 22:35

yeah, but definitely crap for concatenating strings...

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CPallini21-Nov-07 22:46

21-Nov-07 22:46

I don't agree completely, I mean: it is a good general rule to prevent newbies to use such a construct, but there are places where it is handy (I use a similar approach with the infamous goto statement).
This is, at least, my opinion.

Smile | :)

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.

jhwurmbach22-Nov-07 0:38

22-Nov-07 0:38

I use it in some crude way of code generation:
I can automagically declare an Interface and define a smart-ptr type to it by just writing INTERFACE(Name)

George_George22-Nov-07 1:26

Re: Smarter ways to define MACRO to strings? [modified]

22-Nov-07 1:26

Hi jhwurmbach,

I have tried to use ##, but the code does not compile.

<br />
#define PREFIX(x) _T("FOO")##x<br />
<br />
int main()<br />
{<br />
<br />
	const TCHAR* SecondArray [2] = {_T("FILE1"), _T("FILE2")};<br />
<br />
	TCHAR* p = NULL;<br />
	p = PREFIX(SecondArray [0]);<br />
	p = PREFIX(SecondArray [1]);<br />
<br />
<br />
	return 0;<br />
}<br />

jhwurmbach22-Nov-07 2:08

22-Nov-07 2:08

George_George wrote:
#define PREFIX(x) _T("FOO")##x
p = PREFIX(SecondArray [0]);

Sure.

This would make the compiler see

p = _T("FOO")SecondArray [0];<br />
p = _T("FOO")SecondArray [1];<br />

Not exactly what you want.
Remember, we are doing text-replacement here. The C++compiler is not running. Not the slightest trace of C++ at this level!

What we are trying to use here is called the Token-Pasting Operator as I just looked up

You want to write something like

#define PREFIX( x ) _T("FOO##x")<br />
const TCHAR* SecondArray [2] = { PREFIX(FILE1), PREFIX(FILE2)};

-- modified at 8:52 Thursday 22nd November, 2007
Corrected the issue toxcct found

toxcct22-Nov-07 2:48

toxcct

22-Nov-07 2:48

jhwurmbach wrote:
Sure. This would make the compiler see
p = FOOSecondArray [0];
p = FOOSecondArray [1];

no, the compiler sees :

p = _T("FOO")SecondArray [0];
p = _T("FOO")SecondArray [1];

jhwurmbach wrote:
You want to write something like
#define PREFIX( x ) _T("FOO##x")

not either. this will be transformated into

p = _T("FOOSecondArray [0]");

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jhwurmbach22-Nov-07 2:51