Hi Hugo,
> >
> > Thanks Axel. It is stranger yet:
> > 1. mutrec is defined in aa.cpp
> > 2. It is used as extern in mc.cpp, grafrs.cpp and setfile.cpp
> > 3. But g++-4.5 only finds undefined referenes in mc.cpp and grafrs.cpp,
> > *not* in setfile.cpp
> > 4. Yet the extern for mutrec is defined in all three the same way.
> > 5. And previous compilers have found no errors.
> > 6. The whole bunch is linked together via aa.pro that is used in
> > 'qmake-qt4 -o Makefile aa.pro' to create a makefile for make.
> Some updates from my checks:
> a) I can't compile the code on amd64: in tranrs.cpp, lines 1789 and 1810
> you convert "double *" to "int". However, on amd64 "double *" is of
> size 8 bytes, "int" is only 4 bytes ==> You loose precision and get
> quite unpredictable results. In addition, g++ from squeeze and wheezy
> (4.4 and 4.5) do NOT compile it. Chaning "int" to "long", it works
> correctly (maybe the "correct" type would be std::ptrdiff_t?)
>
> b) The linker error: There is a difference between mc.cpp grafrs.cpp AND
> setfile.cpp:
> - setfile: you have "extern mutrc" OUTSIDE of all functions
> - mc and grafrs: the extern mutrc appears IN a function (drwts and
> weights)
> Maybe that's the critical point?
I succeeded to create a testcase:
a.cc:
extern struct {int cnt;} mutrec;
int main(){
mutrec.cnt = 2;
}
b.cc:
struct{ int cnt; } mutrec = { 0};
This compiles fine with g++-4.4, but not with g++-4.5
(just try "g++-4.4 a.cc b.cc" and "g++-4.5 a.cc b.cc")
g++-4.5 states:
/tmp/cc06Uy69.o: In function `f()':
a.cc:(.text+0x6): undefined reference to `mutrec'
collect2: ld returned 1 exit status
However, both versions mention the problem:
a.cc:2:28: warning: non-local variable ‘f()::<anonymous struct> mutrec’ uses
anonymous type
b.cc:1:23: warning: non-local variable ‘<anonymous struct> mutrec’ uses
anonymous type
So, it compiles & links fine if you give those structures a name (e.g.
call them "A"):
a.cc:
extern struct A {int cnt;} mutrec;
int main(){
mutrec.cnt = 2;
}
b.cc:
struct A { int cnt; } mutrec = { 0};
Then, both g++-4.4 and g++-4.5 succeed to link the code.
However, I'm not sure what the C++-standard says to this problem --
should it work with anonymous structures or not?
HTH,
Axel
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Archive: http://lists.debian.org/20110313140515.GQ11958@axel
