C++ switches -O2; -static; -lm ...

blowguy · Post by **blowguy** » Tue Apr 25, 2006 8:50 pm

Ok it would be very nice if someone would introduce us with c++ flags(-O2 -static -lm ...) Or atleast pass a link, because in google it is really hard to find any useful info abot because google is not able to find minus.

I know when -O2 flag is in use, my program is twice faster, but why?

And how to add switches in c++ source code, not in compiler command line!

mf · Post by mf » Tue Apr 25, 2006 9:01 pm

http://www.google.com/search?q=man+gcc

And how to add switches in c++ source code, not in compiler command line!

Well, you can't. A (very limited) substitution is #pragma directives.

because in google it is really hard to find any useful info abot because google is not able to find minus.

rotfl, minus tells google to exclude the word after the minus from the search

e.g. 'apple -banana' should return pages containing 'apple', but not containing 'banana'.

Darko · Post by **Darko** » Wed Apr 26, 2006 12:43 am

You can try enclosing the term in quotes, like "-O2", for example.

blowguy · Post by **blowguy** » Wed Apr 26, 2006 4:58 pm

mf wrote:http://www.google.com/search?q=man+gcc

And how to add switches in c++ source code, not in compiler command line!
Well, you can't. A (very limited) substitution is #pragma directives.

because in google it is really hard to find any useful info abot because google is not able to find minus.
rotfl, minus tells google to exclude the word after the minus from the search
e.g. 'apple -banana' should return pages containing 'apple', but not containing 'banana'.

Thanks a lot... Those keywords really helped me!
Is there any way i can include swicth -O2 in source???

I mean something like "#pragma -O2"

mf · Post by mf » Wed Apr 26, 2006 6:16 pm

Is there any way i can include swicth -O2 in source???

I don't think it's possible with gcc.

I've heard that on some compilers you can control optimizations in this way:

Code: Select all

#pragma optimization_level X

BUT: gcc does not support it.

Moha · Post by **Moha** » Thu Apr 27, 2006 9:41 am

The best way to use predefined option for all source code, (I don't recommand this) is use some system variable/ or writing a generic Make file.

misof · Post by **misof** » Thu Apr 27, 2006 10:44 am

Moha wrote:The best way to use predefined option for all source code, (I don't recommand this) is use some system variable/ or writing a generic Make file.

While your answer is technically correct, I assume that the intended question here was "Can I do something to force the UVa compiler to optimize my code?"

And there, the answer is "No." and your suggestions don't help.

blowguy · Post by **blowguy** » Sat Apr 29, 2006 3:05 pm

misof wrote:
Moha wrote:The best way to use predefined option for all source code, (I don't recommand this) is use some system variable/ or writing a generic Make file.
While your answer is technically correct, I assume that the intended question here was "Can I do something to force the UVa compiler to optimize my code?"

And there, the answer is "No." and your suggestions don't help.

No You are wrong. I don`t need to optimize my code for uva... I believe that on-line judge automatically do that for me.

mf · Post by mf » Sat Apr 29, 2006 3:34 pm

blowguy wrote:I believe that on-line judge automatically do that for me.

Well, I don't know exact gcc switches used by UVa,
But definately, optimization is OFF!

Darko · Post by **Darko** » Sat Apr 29, 2006 6:22 pm

From what I understand they compile only with -lm switch.

Moha · Post by **Moha** » Sun Apr 30, 2006 2:23 am

I know UVA doesn't add any optimization option for compiling.
Sometimes adding optimazation to code result in a bad code.(ie. in class constructors it may cause a bad shallow copy!) but it dependes on your!

blowguy · Post by **blowguy** » Mon May 08, 2006 9:49 pm

http://www.verba.com.ua/some-files/HopcroftKarp.dpr