Dear Boost Experts --
I'm using g++ 4.2.1, OS X 10.6.1, boost 1.40, although I have also
seen this on linux. In attempting to
understand how boost::serialization works, I've stumbled across the
following curiosity. The following
program compiles and runs fine (I've eliminated diagnostic output
which verifies the serialization.)
#include <iostream>
#include <fstream>
#include
#include
struct A {
int v;
template<class Ar>
void serialize(Ar & ar, const unsigned int ver) {
ar & v;
}
};
int
main(int ac, char ** argv) {
A a; a.v = 10;
A * a1p = &a;
const char * fname = "test.bin";
{
std::ofstream ofs(fname);
boost::archive::binary_oarchive ar(ofs);
ar << a1p;
}
A * a2p;
{
std::ifstream ifs(fname);
boost::archive::binary_iarchive ar(ifs);
ar >> a2p;
}
return 0;
}
However, if I add a static_cast to either a1p or a2p (which are
already declared to be type A*) in
the serialization / deserialization lines, it fails to compile:
#include <iostream>
#include <fstream>
#include
#include
struct A {
int v;
template<class Ar>
void serialize(Ar & ar, const unsigned int ver) {
ar & v;
}
};
int
main(int ac, char ** argv) {
A a; a.v = 10;
A * a1p = &a;
const char * fname = "test.bin";
{
std::ofstream ofs(fname);
boost::archive::binary_oarchive ar(ofs);
ar << static_cast(a1p);
}
A * a2p;
{
std::ifstream ifs(fname);
boost::archive::binary_iarchive ar(ifs);
ar >> static_cast(a2p);
}
return 0;
}
Compilation started at Fri Oct 23 14:31:17
make -k debug
make all "CXX_FLAGS = -g -fno-inline -m64 -I. -I..
-I/opt/local/include -Wall -Wextra -Wpointer-
arith -Wcast-align -Wwrite-strings -Wconversion -Woverloaded-virtual
-Wno-sign-compare -Wno-
unused -fno-nonansi-builtins" \
"LD_FLAGS = -g -m64"
g++ -g -fno-inline -m64 -I. -I.. -I/opt/local/include -Wall -Wextra
-Wpointer-arith -Wcast-align -
Wwrite-strings -Wconversion -Woverloaded-virtual -Wno-sign-compare
-Wno-unused -fno-
nonansi-builtins -c test.cc -o test.o
test.cc: In function 'int main(int, char**)':
test.cc:25: error: no match for 'operator<<' in 'ar << a1p'
/opt/local/include/boost/archive/detail/interface_oarchive.hpp:63:
note: candidates are: Archive&
boost::archive::detail::interface_oarchive<Archive>::operator<<(T&)
[with T = A*, Archive =
boost::archive::binary_oarchive]
test.cc:33: error: no match for 'operator>>' in 'ar >> a2p'
/opt/local/include/boost/archive/detail/interface_iarchive.hpp:60:
note: candidates are: Archive&
boost::archive::detail::interface_iarchive<Archive>::operator>>(T&)
[with T = A*, Archive =
boost::archive::binary_iarchive]
make[1]: *** [test.o] Error 1
make[1]: Target `all' not remade because of errors.
make: *** [debug] Error 2
Compilation exited abnormally with code 2 at Fri Oct 23 14:31:18
This completely boggles my mind. My limited understanding suggests
the compiler should not be able
to distinguish between the two programs! I can put the cast on either
one of the two pointers and it
fails, and using an old style cast to A* also fails. I seem to not
understand what boost::serialization is
doing generally, so I was hoping the answer to this question (which is
obviously a theoretical curiosity
and of no practical value) would lead to further insight.
Best regards,
Ben
