🚀 go-pugleaf

mccrory@tomato.fnal.gov (Elliott McCrory) writes:

>How has the use of "static" changed since g++ 1.39?  I have a
>situation like this:

>% cat world.cxx
>#include <std.h>
>#include <stream.h>

>class Foo {
>  static int a;
> public:
>  Foo(int c) { a=c ; f=0.0; };
>  int b() { return a; };
>  static float f;
>};

// Explicit declarations for static members:
int Foo::a;
float Foo::f;


>int main(int argc, char* argv[])
>{
>  Foo A(1);
>  cout << A.b() << "Hello world\n" << A.f << "\n";
>}

>% make -k world
>g++  -g -Dsun4 -DEBUG -o world world.cxx
>world.cxx:7 (world.o): Undefined symbol __3Foo$a referenced from text segment
>world.cxx:7 (world.o): Undefined symbol __3Foo$a referenced from text segment
>world.cxx:7 (world.o): Undefined symbol __3Foo$f referenced from text segment
>world.cxx:7 (world.o): Undefined symbol __3Foo$f referenced from text segment
>world.cxx:8 (world.o): Undefined symbol __3Foo$a referenced from text segment
>world.cxx:8 (world.o): Undefined symbol __3Foo$a referenced from text segment
>world.cxx:15 (world.o): Undefined symbol __3Foo$f referenced from text segment
>world.cxx:15 (world.o): Undefined symbol __3Foo$f referenced from text segment
>*** Error code 1
>make: Warning: Target `world' not remade because of errors

The problem is that all static members must be declared outside of the
class scope. I don't know if they need to have global linkage but that is
usually how I do it. But the code that I added above should work

>Compilation finished at Thu Apr  9 16:13:14

>Thanks in advance.
>--
>  ||    Elliott McCrory, Ph. D.		| mccrory@tomato.fnal.gov (internet)
>-/  \-  Fermi National Accelerator Lab	| ALMOND::MCCRORY	 (DECnet)
>-\  /-  Batavia, IL  60510		| MCCRORY@FNALAD	 (BITnet)
>  ||    708-840-4808			| linac!tomato!mccrory	 (uucp)

Tal Lancaster

Seems like a kludge.  Why has static been abandoned?
--
  ||    Elliott McCrory, Ph. D.		| mccrory@tomato.fnal.gov (internet)
-/  \-  Fermi National Accelerator Lab	| ALMOND::MCCRORY	 (DECnet)
-\  /-  Batavia, IL  60510		| MCCRORY@FNALAD	 (BITnet)
  ||    708-840-4808			| linac!tomato!mccrory	 (uucp)

In article <MCCRORY.92Apr10161734@tomato.fnal.gov> mccrory@tomato.fnal.gov (Elliott McCrory) writes:
>Seems like a kludge.  Why has static been abandoned?

static has not been abandoned; the change in g++-2.0 is that the
compiler now implements what Ellis and Stroustrup specify in the ARM.
In the example, the code was buggy, even though it compiled and ran
under old g++.  The code might or might not have linked successfully
under cfront; it depends on whether the C compiler underneath enforces
the "one definition" rule or not.  That is, in some C compilers if
a bunch of different files declare

extern int foo;

then no one has defined foo: it's an undefined symbol.  In others,
a definition of foo with value zero will appear.  But the ANSI C
standard calls for a definition for each object: a conforming program
has to have "int foo;" somewhere.

In the same way, for each static class variable declared in the class
definition there must exist somewhere an initializer for that variable.
Many compilers kludge one up if none is specified by using the "common
block" technique, but this is contrary to the ARM (think of it as an
extension g++ no longer supports).

If you say

class Bar {
	...
};

class Foo {
	...
	static Bar fooStaticMember;
};

you must, in some source file that includes Foo's definition, say

Bar Foo::fooStaticMember;

If you want to give arguments to the Bar constructor, say

Bar Foo::fooStaticMember(arg1,arg2,...);

If it's an integer, and you want to give a value, say

int Foo::fooStaticInt = 3;

or some such.



--
Joe Buck	jbuck@ohm.berkeley.edu

mccrory@tomato.fnal.gov (Elliott McCrory) writes:

>Seems like a kludge.  Why has static been abandoned?

Well, I got the idea of my so called "kludge" from p. 179 the ARM:

"A static member is not part of objects of a class.  Static members
of a global class have external linkage.  The declaration of a static
data member in its class declaration is NOT a definition.  A definition
is required elsewhere."

As a side note the "kludge" isn't needed when using ATT 3.0.

Tal