C / C++ / MFC

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.

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_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

CPallini

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

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

CPallini

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

21-Nov-07 22:35

yeah, but definitely crap for concatenating strings...

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CPallini21-Nov-07 22:46

CPallini

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

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

22-Nov-07 2:51

Part 1
Yes, you are right. I am glad I do not work as a Text-Preprocessor...
Big Grin | :-D

Part 2
Not when I write
PREFIX(FILE1)
That would indeed become
_T("FOOFILE1")
Big Grin | :-D

toxcct22-Nov-07 4:18

22-Nov-07 4:18

you're probably right, but infortunately, i have no compiler with me at the moment.

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George_George22-Nov-07 18:21

22-Nov-07 18:21

Hi jhwurmbach,

I think your code does not compile. Are there anything wrong?\

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

main.cpp(9) : error C2143: syntax error : missing '}' before ';'
main.cpp(9) : error C2143: syntax error : missing ';' before ','
main.cpp(12) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
main.cpp(12) : error C2040: 'p' : 'int' differs in levels of indirection from 'TCHAR *'
main.cpp(12) : error C2065: 'SecondArray' : undeclared identifier
main.cpp(13) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
main.cpp(13) : error C2040: 'p' : 'int' differs in levels of indirection from 'TCHAR *'
main.cpp(16) : error C2059: syntax error : 'return'
main.cpp(17) : error C2059: syntax error : '}'
main.cpp(17) : error C2143: syntax error : missing ';' before '}'
main.cpp(17) : error C2059: syntax error : '}'

regards,
George

jhwurmbach22-Nov-07 21:27

22-Nov-07 21:27

As toxcct said quite rude, you do not bother to read up the hints we give you.

The way you defined the macro, the line looks to the compiler like
const TCHAR* SecondArray [2] = {_T("FOO_T("FILE1")");, _T("FOO_T("FILE2")");};

And you wonder why it does not compile?
Remember: ##x in the macro-definition is replaced with whatever is written in the braces after PREFIX

George_George22-Nov-07 21:50