I am using boost serialization, mostly the intrusive version. For a template Matrix class I would like to have the non-intrusive version which works on Visual Studio with the following code:
namespace boost
{
namespace serialization
{
template<class Archive, int R, int C, class ElementType>
void serialize(Archive & ar, Matrix<R, C, ElementType> & m, const unsigned int version)
{
ar & ...
}
}
}
int R, int C are the row and columns, ElementType is double or float.
However, this does not work on GCC 4.3.2 with the error
error: 'class Matrix<1u, 3u, double>' has no member named 'serialize'
If I use a special form like
namespace boost
{
namespace serialization
{
template<class Archive>
void serialize(Archive & ar, Matrix<3,1,double> & m, const unsigned int version)
{
ar & ...
}
}
}
it compiles on GCC, but of course only for a special set of template arguments.
What can I do to make it work on both compilers for all R, C and ElementType?
EDIT: These are the lines causing the error:
/[myfolder]/lib/BOOST/1_44_0/include/boost/serialization/access.hpp: In static member function 'static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T = Matrix<3u, 1u, double>]':
/[myfolder]/lib/BOOST/1_44_0/include/boost/serialization/serialization.hpp:70: instantiated from 'void boost::serialization::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T = Matrix<3u, 1u, double>]'
/[myfolder]/lib/BOOST/1_44_0/include/boost/serialization/serialization.hpp:129: instantiated from 'void boost::serialization::serialize_adl(Archive&, T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T = Matrix<3u, 1u, double>]'
/[myfolder]/lib/BOOST/1_44_0/include/boost/archive/detail/iserializer.hpp:182: instantiated from 'void boost::archive::detail::iserializer<Archive, T>::load_object_data(boost::archive::detail::basic_iarchive&, void*, unsigned int) const [with Archive = boost::archive::binary_iarchive, T = Matrix<3u, 1u, double>]'
It looks like a signed/unsigned mismatch to me. Your template function is declared with ints but the error indicates that the object which it's trying to match with the template has parameters 1u and 3u. When you instantiate the object that you're trying to serialize, are you using unsigned values for the dimensions? Try changing your serialize template function to take unsigneds or instantiating your Matrix with ints.
Related
I have a class with a constructor but the compilation fails with the error:
error: use of deleted function 'std::atomic<long unsigned int>::atomic(const std::atomic<long unsigned int>&)'
I'm struggling to understand what this error means. I've been trying to update some code from using tbb::atomic to using std::atomic, and this error wasn't appearing before with tbb::atomic.
The bit of code that upsets the compiler is:
#include <boost/aligned_storage.hpp>
template <typename T>
class Holder<T,true>
{
public:
//! Construct a value (there mustn't be one already)
template <typename ARG>
void Construct(const ARG &arg) { new(Raw()) T(arg); }
private:
typename boost::aligned_storage<sizeof(T), boost::alignment_of<T>::value>::type impl;
void *Raw() { return &impl; }
};
Specifically the line:
void Construct(const ARG &arg) { new(Raw()) T(arg); }
I'd be very grateful if anyone could help me understand what is going on.
EDIT:
Full error message:
holder.hpp:75:34: error: use of deleted function 'std::atomic<long unsigned int>::atomic(const std::atomic<long unsigned int>&)'
75 | void Construct(const T &arg) { new(Raw()) T(arg); }
| ^~~~~~~~~~~~~~~~~
In file included from /include/TPtools/boost/smart_ptr/detail/sp_counted_base_std_atomic.hpp:19,
from /include/TPtools/boost/smart_ptr/detail/sp_counted_base.hpp:48,
from /include/TPtools/boost/smart_ptr/detail/shared_count.hpp:29,
from /include/TPtools/boost/smart_ptr/shared_ptr.hpp:28,
from /include/TPtools/boost/shared_ptr.hpp:17,
from movegate.cpp:14:
/pkgsData/gcc-v9.3.0p1/Linux/RHEL6.0-2013-x86_64/include/c++/9.3.0/atomic:824:7: note: declared here
824 | atomic(const atomic&) = delete;
| ^~~~~~
holder.hpp: In instantiation of 'void Holder<T, true>::Construct(const T&) [with T = std::atomic<long unsigned int>; T = std::atomic<long unsigned int>]':
element.hpp:185:9: required from 'void Element<PRESENT, ABSENT>::Accessor<PRESENCE>::MakePresentImpl(const ARG&) const [with ARG = std::atomic<long unsigned int>; PRESENCE = Cluster<Element<std::atomic<long unsigned int>, Link>, true>::NonLockingPresence; PRESENT = std::atomic<long unsigned int>; ABSENT = Link]'
element.hpp:119:7: required from 'Element<PRESENT, ABSENT>::PresentResult Element<PRESENT, ABSENT>::Accessor<PRESENCE>::MakePresent(const ARG&) const [with ARG = std::atomic<long unsigned int>; PRESENCE = Cluster<Element<std::atomic<long unsigned int>, Link>, true>::NonLockingPresence; PRESENT = std::atomic<long unsigned int>; ABSENT = Link; Element<PRESENT, ABSENT>::PresentResult = std::atomic<long unsigned int>&]'
dispenser.hpp:78:5: required from 'Index Dispenser<T>::Insert(const T&) [with T = std::atomic<long unsigned int>]'
I have a Register function which takes a std::function<void(const uint8_t* data, size_t len)> as a parameter. I want to use the member function of an object as the target.
I found this question according to which the answer is to use std::bind to bind the first first argument (the implicit this pointer) to the actual object pointer and then use it as the std::function argument.
This however doesn't work anymore in neither C++11, C++14 nor C++17?
Consider the following test program.
#include <iostream>
#include <cstdint>
#include <functional>
void Register(std::function<void(const uint8_t* data, size_t len)> func) {
//Dummy - directly call into function
func(nullptr, 0);
}
class TestClass {
public:
void TestRegister() {
Register(
std::bind(&TestClass::TestTarget, this, std::placeholders::_1)
);
}
void TestTarget(const uint8_t* data, size_t len) {
(void) data;
(void) len;
std::cout << "Hello there" << std::endl;
}
};
int main() {
TestClass testObj;
testObj.TestRegister();
return 0;
}
When compiling for -std=c++17 this throws a rather cryptic error message (I have no idea what it's trying to say here with Wrong number of arguments for pointer-to-member):
In file included from /home/max/Documents/TestingFunctions/main.cpp:3:0:
/usr/include/c++/7/functional: In instantiation of ‘struct std::_Bind_check_arity<void (TestClass::*)(const unsigned char*, long unsigned int), TestClass*, const std::_Placeholder<1>&>’:
/usr/include/c++/7/functional:854:12: required from ‘struct std::_Bind_helper<false, void (TestClass::*)(const unsigned char*, long unsigned int), TestClass*, const std::_Placeholder<1>&>’
/usr/include/c++/7/functional:875:5: required by substitution of ‘template<class _Func, class ... _BoundArgs> typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type std::bind(_Func&&, _BoundArgs&& ...) [with _Func = void (TestClass::*)(const unsigned char*, long unsigned int); _BoundArgs = {TestClass*, const std::_Placeholder<1>&}]’
/home/max/Documents/TestingFunctions/main.cpp:14:78: required from here
/usr/include/c++/7/functional:841:7: error: static assertion failed: Wrong number of arguments for pointer-to-member
static_assert(_Varargs::value
^~~~~~~~~~~~~
/home/max/Documents/TestingFunctions/main.cpp: In member function ‘void TestClass::TestRegister()’:
/home/max/Documents/TestingFunctions/main.cpp:14:26: error: could not convert ‘std::bind(_Func&&, _BoundArgs&& ...) [with _Func = void (TestClass::*)(const unsigned char*, long unsigned int); _BoundArgs = {TestClass*, const std::_Placeholder<1>&}; typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type = std::_Bind<void (TestClass::*(TestClass*, std::_Placeholder<1>))(const unsigned char*, long unsigned int)>](((TestClass*)this), std::placeholders::_1)’ from ‘std::_Bind_helper<false, void (TestClass::*)(const unsigned char*, long unsigned int), TestClass*, const std::_Placeholder<1>&>::type {aka std::_Bind<void (TestClass::*(TestClass*, std::_Placeholder<1>))(const unsigned char*, long unsigned int)>}’ to ‘std::function<void(const unsigned char*, long unsigned int)>’
std::bind(&TestClass::TestTarget, this, std::placeholders::_1)
~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Replacing the TestRegister function with one that does the exact same thing in a lambda expression compiles and runs without problems.
void TestRegister() {
Register(
[this](const uint8_t* data, size_t len) {
TestTarget(data, len);
}
);
}
Question: Why does the std::bind approach from the linked question not work? Was this feature removed or do I have an error in my code?
Your function Register expects a function with two parameters, but you try to pass to it a function with one placeholded parameter.
void TestRegister() {
Register(
std::bind(&TestClass::TestTarget, this, std::placeholders::_1, std::placeholders::_2)
);
}
Your function takes two parameters, while you are only passing one placeholder.
std::bind(&TestClass::TestTarget, this, std::placeholders::_1, std::placeholders::_2);
How to serialize a class with a boost::dynamic_bitset member?
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/dynamic_bitset.hpp>
#include <boost/serialization/bitset.hpp>
#include <sstream>
class A
{
friend class boost::serialization::access;
boost::dynamic_bitset<> x;
template<class Archive>
void serialize(Archive & ar, const unsigned int){
ar & x;
}
};
int main()
{
A a;
std::stringstream ss;
boost::archive::text_oarchive oa(ss);
oa << a;
return 0;
}
Compiling gives an error (boost 1.57)
In file included from /usr/include/boost/serialization/extended_type_info_typeid.hpp:37:0,
from /usr/include/boost/archive/detail/oserializer.hpp:38,
from /usr/include/boost/archive/detail/interface_oarchive.hpp:23,
from /usr/include/boost/archive/detail/common_oarchive.hpp:22,
from /usr/include/boost/archive/basic_text_oarchive.hpp:32,
from /usr/include/boost/archive/text_oarchive.hpp:31,
from dynamic_bitset_setial.cpp:1:
/usr/include/boost/serialization/access.hpp: In static member function ‘static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’:
/usr/include/boost/serialization/serialization.hpp:69:5: instantiated from ‘void boost::serialization::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’
/usr/include/boost/serialization/serialization.hpp:128:9: instantiated from ‘void boost::serialization::serialize_adl(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’
/usr/include/boost/archive/detail/oserializer.hpp:148:5: instantiated from ‘void boost::archive::detail::oserializer<Archive, T>::save_object_data(boost::archive::detail::basic_oarchive&, const void*) const [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’
dynamic_bitset_setial.cpp:25:1: instantiated from here
/usr/include/boost/serialization/access.hpp:118:9: error: ‘class boost::dynamic_bitset<>’ has no member named ‘serialize’
I went ahead and filed the pull request to add Serialization support to Boost Dynamic Bitset
Serialization using the public interface isn't optimal as to_block_range()/from_block_range() require copying of m_bits (and subsequent resize()).
I added a generic implementation to Boost Dynamic Bitset. The changes merge cleanly against develop or master (1_58_0).
Changes
Implementation added with
minimal intrusiveness, only a nested friend (class serialization_impl;) has been forward declared to "key-hole" the required friend access through
This class, as well as the actual ADL hook for Boost Serialization are implemented in a separate header (dynamic_bitset/serialization.hpp, similar to other boost libraries with serialization support).
This means that zero dependencies on Boost Serialization stuff exists unless boost/dynamic_bitset/serialization.hpp is actually included
Zero copy is achieved (leveraging std::vector<Block>'s builtin support in Boost Serialization)
Tests
The second commit in the pull request adds tests for this feature. I'm not sure how to add the dyn_bitset_unit_tests5.cpp to the Jamfile. I suppose something else must be done to ensure linking to Boost System and Boost Serialization. I have run the tests myself using a simple wrapper:
#include <modular-boost/libs/dynamic_bitset/dyn_bitset_unit_tests5.cpp>
int main() {
test_main(0, nullptr);
}
Which can then be compiled and run with e.g.
g++ main.cpp -lboost_system -lboost_serialization && ./a.out
No output means no errors.
dynamic_bitset<> is not serializable, as you've found out (std::bitset<N> is different type).
Not to worry, though, you can add it without too much effort:
namespace boost { namespace serialization {
template <typename Ar, typename Block, typename Alloc>
void save(Ar& ar, dynamic_bitset<Block, Alloc> const& bs, unsigned) {
size_t num_bits = bs.size();
std::vector<Block> blocks(bs.num_blocks());
to_block_range(bs, blocks.begin());
ar & num_bits & blocks;
}
template <typename Ar, typename Block, typename Alloc>
void load(Ar& ar, dynamic_bitset<Block, Alloc>& bs, unsigned) {
size_t num_bits;
std::vector<Block> blocks;
ar & num_bits & blocks;
bs.resize(num_bits);
from_block_range(blocks.begin(), blocks.end(), bs);
bs.resize(num_bits);
}
template <typename Ar, typename Block, typename Alloc>
void serialize(Ar& ar, dynamic_bitset<Block, Alloc>& bs, unsigned version) {
split_free(ar, bs, version);
}
} }
This works e.g. Live On Coliru
int main() {
A a;
for (int i=0; i<128; ++i)
a.x.resize(11*i, i%2);
std::stringstream ss;
{
boost::archive::text_oarchive oa(ss);
oa << a;
}
std::cout << ss.str();
{
boost::archive::text_iarchive ia(ss);
A b;
ia >> b;
assert(a.x == b.x);
}
}
Note that if you can't afford to copy the blocks vector, it's equally easy to add serialization directly on the m_bits level, but that requires intrusive changes (friend access required at a minimum).
Such a thing would easily be added to boost in a pull request.
Update added that pull request
I am compiling a c++ code on a linux ubuntu with g++4.8.1 and boost 1.55.0.
My program uses a class A, which has a member table which is an unsigned long long array. The same class has other members which are simple int. I am using boost to serialize my data.
My code work and compile all fine, if I serialize all but the table in A.
However it does not compile if I try to serialize table. I get the following error:
/usr/local/include/boost/serialization/access.hpp: In instantiation of ‘static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive; T = long long unsigned int]’:
/usr/local/include/boost/serialization/access.hpp: In instantiation of ‘static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive; T = long long unsigned int]’:
/usr/local/include/boost/serialization/serialization.hpp:69:69: required from ‘void boost::serialization::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive; T = long long unsigned int]’
/usr/local/include/boost/serialization/serialization.hpp:128:27: required from ‘void boost::serialization::serialize_adl(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive; T = long long unsigned int]’
/usr/local/include/boost/archive/detail/oserializer.hpp:152:5: required from ‘void boost::archive::detail::oserializer<Archive, T>::save_object_data(boost::archive::detail::basic_oarchive&, const void*) const [with Archive = boost::archive::text_oarchive; T = long long unsigned int]’
/usr/local/include/boost/archive/detail/oserializer.hpp:101:1: required from ‘class boost::archive::detail::oserializer<boost::archive::text_oarchive, long long unsigned int>’
/usr/local/include/boost/archive/detail/oserializer.hpp:214:5: required from ‘boost::archive::detail::pointer_oserializer<Archive, T>::pointer_oserializer() [with Archive = boost::archive::text_oarchive; T = long long unsigned int]’
/usr/local/include/boost/serialization/singleton.hpp:106:7: [ skipping 95 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/usr/local/include/boost/archive/detail/oserializer.hpp:314:44: required from ‘static void boost::archive::detail::save_non_pointer_type<Archive>::invoke(Archive&, T&) [with T = Metapop; Archive = boost::archive::text_oarchive]’
/usr/local/include/boost/archive/detail/oserializer.hpp:525:24: required from ‘void boost::archive::save(Archive&, T&) [with Archive = boost::archive::text_oarchive; T = Metapop]’
/usr/local/include/boost/archive/detail/common_oarchive.hpp:69:40: required from ‘void boost::archive::detail::common_oarchive<Archive>::save_override(T&, int) [with T = Metapop; Archive = boost::archive::text_oarchive]’
/usr/local/include/boost/archive/basic_text_oarchive.hpp:80:9: required from ‘void boost::archive::basic_text_oarchive<Archive>::save_override(T&, int) [with T = Metapop; Archive = boost::archive::text_oarchive]’
/usr/local/include/boost/archive/detail/interface_oarchive.hpp:63:9: required from ‘Archive& boost::archive::detail::interface_oarchive<Archive>::operator<<(T&) [with T = Metapop; Archive = boost::archive::text_oarchive]’
simulation.cpp:1403:9: required from here
/usr/local/include/boost/serialization/access.hpp:118:9: error: request for member ‘serialize’ in ‘t’, which is of non-class type ‘long long unsigned int’
t.serialize(ar, file_version);
^
I have read aroud that if I used vectors or/and an other data type it would work. However it is critical for me (for speed) to use a raw array of unsigned long long. Any idea ?
Thnaks a lot for you help !
Serializing unsigned long long arrays works for me using gcc 4.7.2 with boost 1.49, gcc 4.2.1 with boost 1.55, and clang 3.4 with boost 1.55:
#include <sstream>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/serialization/access.hpp>
#include <boost/version.hpp>
struct Foo {
unsigned long long bar[3];
template<class Archive>
void serialize(Archive& ar, const unsigned int /*version*/) {
ar & bar;
}
};
std::ostream& operator<<(std::ostream& os, const Foo& foo) {
return os << foo.bar[0] << ' ' << foo.bar[1] << ' ' << foo.bar[2];
}
int main() {
std::cout << "Boost version " << BOOST_LIB_VERSION << '\n';
Foo before;
before.bar[0] = 0;
before.bar[1] = 1;
before.bar[2] = 2;
std::cout << "before: " << before << '\n';
std::ostringstream os;
{
boost::archive::text_oarchive oa(os);
oa << before;
}
Foo after;
{
std::istringstream is(os.str());
boost::archive::text_iarchive ia(is);
ia >> after;
}
std::cout << "after: " << after << '\n';
return 0;
}
Here's gcc 4.8 with boost 1.55 on Coliru, also works.
If you are using a pointer to an allocated array, then I think that is your problem. I don't believe you can serialize a bare pointer to a primitive, and I'm sure you can't serialize a bare pointer to an array of primitives because there is no way for serialization to know how many elements a pointer points to.
I would use a std::vector over an allocated array because there is no speed disadvantage in doing so. However, if you really want to allocate your own array then you can serialize it with the boost::serialization::make_array() wrapper like this:
#include <iostream>
#include <boost/archive/text_oarchive.hpp>
#include <boost/serialization/access.hpp>
#include <boost/serialization/array.hpp>
struct Foo {
size_t dataSize;
unsigned long long *data;
Foo()
: dataSize(3)
, data(new unsigned long long[dataSize]) {
}
~Foo() {
delete[] data;
}
// TODO: Production code should disallow default copy constructor
// and assignment operator.
template<class Archive>
void serialize(Archive& ar, const unsigned int /*version*/) {
ar & dataSize;
ar & boost::serialization::make_array(data, dataSize);
}
};
int main() {
Foo foo;
foo.data[0] = 0;
foo.data[1] = 1;
foo.data[2] = 2;
boost::archive::text_oarchive oa(std::cout);
oa << foo;
return 0;
}
It turns out that this question was not about unsigned long long at all, but is essentially a duplicate of boost serialization, deserialization of raw C arrays.
I cannot figure out why this segment gives unresolved overloaded function error (gcc version 4.3.4 (Debian 4.3.4-6)):
#include <algorithm>
#include <boost/function.hpp>
// this does not work
int main1()
{
typedef boost::function<const int&(const int&, const int&)> max;
max m(&std::max<int>);
}
// this does not work
int main2() {
typedef boost::function2<const int&, const int&, const int&> max;
max m(static_cast<max>(&std::max<int>));
}
can you help me, thanks
test.cpp: In function âint main()â:
test.cpp:7: error: no matching function for call to âboost::function2<const int&, const int&, const int&>::function2(<unresolved overloaded function type>)â
/usr/include/boost/function/function_template.hpp:747: note: candidates are: boost::function2<R, T1, T2>::function2(const boost::function2<R, T1, T2>&) [with R = const int&, T0 = const int&\
, T1 = const int&]
/usr/include/boost/function/function_template.hpp:739: note: boost::function2<R, T1, T2>::function2(boost::function2<R, T1, T2>::clear_type*) [with R = const int&, T0 = cons\
t int&, T1 = const int&]
/usr/include/boost/function/function_template.hpp:707: note: boost::function2<R, T1, T2>::function2() [with R = const int&, T0 = const int&, T1 = const int&]
max/min is defined as
template<typename _Tp>
inline const _Tp&
max(const _Tp& __a, const _Tp& __b)
{
// concept requirements
__glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
//return __a < __b ? __b : __a;
if (__a < __b)
return __b;
return __a;
}
I have tried all sorts of template explicit instantiation but nothing seems to work. Same problem appears with g++ 4.1 but not with ICC
this works
#include <algorithm>
#include <boost/function.hpp>
namespace std_ {
template<typename _Tp>
inline const _Tp&
max(const _Tp& __a, const _Tp& __b)
{
// concept requirements
//return __a < __b ? __b : __a;
if (__a < __b)
return __b;
return __a;
}
}
int main()
{
typedef const int &T;
typedef boost::function<T(T,T)> min_;
//typedef const int&(*min_)(const int&, const int&);
min_ m(::std_::max<int>);
}
and this
#include <algorithm>
#include <boost/function.hpp>
int main()
{
//typedef const int &T;
//typedef boost::function<T(T,T)> min_;
typedef const int&(*min_)(const int&, const int&);
min_ m(::std::max<int>);
}
Update: this is a gcc bug that has been fixed in gcc >=4.4. bugzilla. Also, revised my answer with a reduced test case.
There are two components to this problem: the way boost::function adopts a function pointer and the gcc bug.
boost::function - There is something strange about the error message you listed in the question; there is no candidate constructor that accepts anything like a function address. Digging into the boost::function src, the relevant constructor is (leaving out the enable_if argument):
template<typename Functor>
function(Functor f) : base_type(f) {}
So boost::function doesn't help you out at all in specifying the type of a function pointer; if the function is overloaded the address must be cast to specify its type. If an overloaded function address is used, the above template can't be instantiated, and therefore the appropriate constructor doesn't show up in the error message.
gcc bug - If you look at the stl_algobase.h header again, you'll see there are two templates named max, a two param version and a one param version. This shouldn't be a problem with you code though, right? The term &max<int> should instantiate the single param version and take its address. However, that is not what happens. You can see the problem in the reduced (no header) test case:
template <class T>
const T& max(const T& x, const T& y){
return x > y ? x : y;
}
template <class T, class C>
const T& max(const T& x, const T& y, C comp){
return comp(x, y) ? y : x;
}
template <class R, class A0, class A1>
struct functor{
template <class F>
functor(F f) : f(f) {}
R (*f)(A0, A1);
};
int main(void){
functor<const int&, const int&, const int&> func(&max<int>);
return 0;
}
The above code results in a unresolved overloaded function type with gcc 4.3.4. The fix is either to remove the template <class T, class C> max(...){...} definition or add a static_cast<const int& (*)(const int&, const int&)>(...) around the function address. I'm guessing the problem has to do with incorrect application of partial explicit parameter specification, which is specified by the standard. It lets you leave out trailing template parameters to do things like specify a return value type and not the argument types. That is, the compiler instantiates both template when it should only instantiate the fully specified template. Its moot speculation though, since the bug has been fixed in gcc >= 4.4.
Since one shouldn't hack at stl_algobase.h ;) , the work around Vicente suggests is the correct one, namely cast the function pointer to the desired function pointer type const int& (*)(const int&, const int&). In your code, the cast doesn't work because, as GMan points out, you are casting to a boost::function<...>, which does nothing to resolve the function pointer ambiguity.
To critique the code, there's no reason to static_cast that. Consider all the cast is going to do is use the constructor of boost::function2 to make a new boost::function2, then it will be copy-constructed into m. Just construct directly into m:
#include <algorithm>
#include <boost/function.hpp>
int main()
{
typedef boost::function2<const int&, const int&, const int&> max;
max m(&std::max<int>);
}
Lastly, the preferred syntax of boost::function is:
#include <algorithm>
#include <boost/function.hpp>
int main()
{
typedef boost::function<const int&(const int&, const int&)> max;
max m(&std::max<int>);
}
The n-ary specific classes are for older compiler support.
It seems to be a problem with the definition of the std::max template function with releases of gcc < 4.4
With gcc-4.4.0 and msvc Express9 it works.
The following works also for gcc-3.4 and gcc-4.3
int main1()
{
int res = std::max(1,2);
typedef boost::function<const int&(const int&, const int&)> max;
max m(static_cast<const int&(*)(const int&, const int&)>(std::max<int>));
return 0
}