Problem with code or gcc?

Problem with code or gcc?

[Kedzierski, Artur CIV NAVSURFWARCENDIV CORONA]

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	Could anybody tell me if this is a valid C++ code or
a problem with GCC?

test_prog.cc:
#include <vector>
struct MyStruct {
	static const int CONST = 1;
};

int main() {
	std::vector<int> l;
	MyStruct z;
	l.push_back(z.CONST);
}


	I get an undefined reference to MyStruct::CONST when 
I try to compile it.
	I appreciate any help.

	Artur Kedzierski

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RE: Problem with code or gcc?

[Philippe Haution]

Hello,

This is not a valid C++ code, you cannot define the
value of CONST inside the struct declaration.

A more correct code would be :

struct MyStruct {
 static const int CONST;
};

const int MyStruct::CONST = 1;

Regards,

PH

--- "Kedzierski, Artur CIV NAVSURFWARCENDIV CORONA"
<artur.kedzierski@navy.mil> a écrit :

> 	Could anybody tell me if this is a valid C++ code
> or
> a problem with GCC?
> 
> test_prog.cc:
> #include <vector>
> struct MyStruct {
> 	static const int CONST = 1;
> };
> 
> int main() {
> 	std::vector<int> l;
> 	MyStruct z;
> 	l.push_back(z.CONST);
> }
> 
> 
> 	I get an undefined reference to MyStruct::CONST
> when 
> I try to compile it.
> 	I appreciate any help.
> 
> 	Artur Kedzierski
> 



	

	
		
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Re: Problem with code or gcc?

[John Love-Jensen]

Hi Artur,

> Shouldn't I get a linker error in those other cases?

Not necessarily.

You won't get a linker error if the actual numeric value can be used "as
is", without referencing the variable it is associated with.  Consider it an
optimization of sorts.

If you really dislike this situation[1], you can use enum for your integer
constants in your struct.

[1] I actually PREFER coding like in your example.  But I know quite a few
C++ software engineers that prefer using enums for constants instead --
they'd claim there are "less surprises".  Both idioms will be supported by
C++ for a very long time.

Sincerely,
--Eljay

RE: Problem with code or gcc?

[Kedzierski, Artur CIV NAVSURFWARCENDIV CORONA]

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	Philippe and Ryan, thank You for your responses.
	One thing that I find it strange is that I can use
MyStruct::CONST in other ways without a problem:

MyStruct m;
int a = m.CONST
std::vector<int> v;
v.push_back(static_cast<int>(m.CONST));
if (b == m.CONST) 
  ...

	However, only when I use 'v.push_back(m.CONST)', I
get a linker error. Shouldn't I get a linker error in
those other cases?


-----Original Message-----
From: Philippe Haution [mailto:philippe_haution@yahoo.fr]
Sent: Tuesday, September 27, 2005 7:13
To: Kedzierski, Artur CIV NAVSURFWARCENDIV CORONA; gcc-help@gcc.gnu.org
Subject: RE: Problem with code or gcc?


Hello,

This is not a valid C++ code, you cannot define the
value of CONST inside the struct declaration.

A more correct code would be :

struct MyStruct {
 static const int CONST;
};

const int MyStruct::CONST = 1;

Regards,

PH

--- "Kedzierski, Artur CIV NAVSURFWARCENDIV CORONA"
<artur.kedzierski@navy.mil> a écrit :

> 	Could anybody tell me if this is a valid C++ code
> or
> a problem with GCC?
> 
> test_prog.cc:
> #include <vector>
> struct MyStruct {
> 	static const int CONST = 1;
> };
> 
> int main() {
> 	std::vector<int> l;
> 	MyStruct z;
> 	l.push_back(z.CONST);
> }
> 
> 
> 	I get an undefined reference to MyStruct::CONST
> when 
> I try to compile it.
> 	I appreciate any help.
> 
> 	Artur Kedzierski
> 



	

	
		
________________________________________________________________________
___ 
Appel audio GRATUIT partout dans le monde avec le nouveau Yahoo!
Messenger 
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RE: Problem with code or gcc?

[Ryan Mansfield]

http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.11


Regards,
 
Ryan Mansfield
 

-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On
Behalf Of Kedzierski, Artur CIV NAVSURFWARCENDIV CORONA
Sent: Tuesday, September 27, 2005 9:40 AM
To: gcc-help@gcc.gnu.org
Subject: Problem with code or gcc?

	Could anybody tell me if this is a valid C++ code or
a problem with GCC?

test_prog.cc:
#include <vector>
struct MyStruct {
	static const int CONST = 1;
};

int main() {
	std::vector<int> l;
	MyStruct z;
	l.push_back(z.CONST);
}


	I get an undefined reference to MyStruct::CONST when 
I try to compile it.
	I appreciate any help.

	Artur Kedzierski