> A few days ago, I was writing a program that had some constants. They were
> all defined in a class and were static constant integers, something like
>
> class foo {
> public:
> static const int X = 5;
> static const int Y = 10;
> static const int Z = 15;
> };
>
> When I would compile my program in Windows XP with mingw g++ 3.4.2, I
> would
> have no problems.
>
> However, when I went to Linux, where I have g++ 3.3.5 (or possibly 3.3.6,
> but I think it's 3.3.5), the linker would complain about unresolved
> symbols.
>
> If I were to define the static variable in my implementation file, the
> linker would find the variables and go on its merry way. In other words, I
> could solve the problem by doing this:
>
> const int foo::X;
> const int foo::Y;
> const int foo::Z;
>
> I didn't even need to declare a value here. It took the value from the
> class-def.
>
> Is this correct behavior? I thought static constant integers could be
> defined completely within the class, because they are simply type-safe
> constants that need no storage space. It seems like it might have been
> wrong
> since in Windows I had g++ 3.4.2 and in Linux I had g++ 3.3.5, but I
> wasn't
> sure.
>
> In Bruce Eckel's "Thinking in C++", he states that "In older versions of
> C++, static const was not supported inside classes." I don't generally
> think
> of g++ 3.3.x as an old compiler, but maybe it is just old enough not to
> support this?
>
> Thanks,
>
> --John Ratliff
>
> -----Original Message-----
> From: Ryan Mansfield [mailto:RMansfield@xxxxxxx]
> Sent: Sunday, October 16, 2005 10:26 AM
> To: 'John Ratliff'; gcc-help@xxxxxxxxxxx
> Subject: RE: C++ static integer class constants...
>
> Yes, it is required that static data members must be defined in exactly
> one
> translation unit.
>
> Please see:
>
> http://gcc.gnu.org/onlinedocs/gcc/Static-Definitions.html#Static-
> Definitions
>
> http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.11
>
> Regards,
>
> Ryan Mansfield
I am asking if static CONSTANTS are different than static member variables.
My understanding of a static constant is that it is like a type-safe local
define. It solves the major problems of #define for creating constants. They
should not need storage space.
And if I am wrong, and they do, then why do they only need storage space for
g++ <= 3.3.5 and not g++ 3.4.2? Is it just an optimization? g++ 3.4.2 never
needed storage space declared, even when I passed -O0 to it. g++ 3.3.5 only
needed storage for 2 of my 8 constants regardless of whether -O0 or -O2 was
used.
This is an example from Bruce Eckel's Thinking in C++ Volume 1. Why does
this program not need to declare storage space for StringStack::size? Is
Bruce Eckel wrong?
-----------------------------------------------
//: C08:StringStack.cpp
// Using static const to create a
// compile-time constant inside a class
#include <string>
#include <iostream>
using namespace std;
class StringStack {
static const int size = 100;
const string* stack[size];
int index;
public:
StringStack();
void push(const string* s);
const string* pop();
};
StringStack::StringStack() : index(0) {
memset(stack, 0, size * sizeof(string*));
}
void StringStack::push(const string* s) {
if(index < size)
stack[index++] = s;
}
const string* StringStack::pop() {
if(index > 0) {
const string* rv = stack[--index];
stack[index] = 0;
return rv;
}
return 0;
}
string iceCream[] = {
"pralines & cream",
"fudge ripple",
"jamocha almond fudge",
"wild mountain blackberry",
"raspberry sorbet",
"lemon swirl",
"rocky road",
"deep chocolate fudge"
};
const int iCsz =
sizeof iceCream / sizeof *iceCream;
int main() {
StringStack ss;
for(int i = 0; i < iCsz; i++)
ss.push(&iceCream[i]);
const string* cp;
while((cp = ss.pop()) != 0)
cout << *cp << endl;
} ///:~
-----------------------------------------------
