Daniel Krügler <dsp@bdal.de> writes:
- Assumption one: Boost does not provide the definitions of potential static constants hidden by the BOOST_STATIC_CONSTANT definition (I used only the headers of the library, so my potential testing bug would be that I had to include the corresponding translation units of boost providing the constant's definitions, but sorry - I did not find them!).
In general BOOST_STATIC_CONSTANT is used within templates, so the definition of a corresponding member may be given in the header file: template <int N> struct int_ { BOOST_STATIC_CONSTANT(int, value = N); }; #ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION template <int N> int const int_<N>::value; #endif
As I said: If this assumption is false, please blame me straight for incomplete testing and for trying to spread bad rumors on this (really!) great library.
It's probably not false in most cases.
- Assumption two: Even if Boost does provide these definitions, there may occur problems due to the VC7.1 flags /Za and /Ze (aka disabling and enabling language extensions), which I will explain in the following. The same point applies as to assumptions one, if I did incomplete testing or testing with rather old boost libraries.
The nasty thing concerning the /Ze flag is that it effectively does not "extend" the language in every case. A small testing case is the following program:
a.h: ------------------------- #ifndef A_H_INC #define A_H_INC struct A { static const int val = 42; // Declaration of a static member variable }; #endif -------------------------
a.cpp -------------------- #include "a.h" const int A::val; // Definition might be needed, if the program accesses // the adress of A::val -------------------------
main.cpp -------------------- #include "a.h" int main() { } -------------------------
Although this is a C++ Standard compliant program, it will not successfully link with the /Ze flag enabled, which is to my opion a real compiler bug (which I already posted to m.p.v.language, but got no reasonable response yet). The obtained error message is:
error LNK2005: "private: static int const A::val" (?val@A@@0HB) already defined in a.obj error LNK2005: "private: static int const A::val" (?val@A@@0HB) already defined in main.obj
Looks like a bug to me.
Question: Is this special deficiency of the VC7.1 compiler taken account in the current boost library?
I doubt it. How would we do that?
I think, it is impossible to demand, that users are enforced to use either only /Ze or only /Za, because each of these choices has some considerable drawbacks (at least on Windows systems...)
Well, it seems to me that we can only respond to actual problems. Do you have an actual case of using a Boost library where these issues cause you trouble? -- Dave Abrahams Boost Consulting www.boost-consulting.com