Could someone tell me why the following won't compile?
#include "a.h"
#include <list>
#include <algorithm>
#include <tr1/functional>
using namespace std;
class B {
public:
B() {
list< A* > aList;
A* a = new A();
lower_bound( aList.begin(), aList.end(), a, tr1::bind( &B::aComp, tr1::placeholders::_1, tr1::placeholders::_2 ) );
}
private:
bool aComp( A* a1, A* a2 );
};
Compile output:
In file included from c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/tr1/functional:56,
from ..\bindTest\/b.h:4,
from ..\bindTest\b.cpp:1:
c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/tr1_impl/functional: In member function 'typename std::tr1::result_of<_Functor(typename std::tr1::result_of<std::tr1::_Mu<_Bound_args, std::tr1::is_bind_expression::value, (std::tr1::is_placeholder::value > 0)>(_Bound_args, std::tr1::tuple<_UElements ...>)>::type ...)>::type std::tr1::_Bind<_Functor(_Bound_args ...)>::__call(const std::tr1::tuple<_UElements ...>&, std::tr1::_Index_tuple<_Indexes ...>) [with _Args = A*&, A* const&, int ..._Indexes = 0, 1, _Functor = std::tr1::_Mem_fn<bool (B::*)(A*, A*)>, _Bound_args = std::tr1::_Placeholder<1>, std::tr1::_Placeholder<2>]':
c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/tr1_impl/functional:1191: instantiated from 'typename std::tr1::result_of<_Functor(typename std::tr1::result_of<std::tr1::_Mu<_Bound_args, std::tr1::is_bind_expression::value, (std::tr1::is_placeholder::value > 0)>(_Bound_args, std::tr1::tuple<_UElements ...>)>::type ...)>::type std::tr1::_Bind<_Functor(_Bound_args ...)>::operator()(_Args& ...) [with _Args = A*, A* const, _Functor = std::tr1::_Mem_fn<bool (B::*)(A*, A*)>, _Bound_args = std::tr1::_Placeholder<1>, std::tr1::_Placeholder<2>]'
c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/bits/stl_algo.h:2495: instantiated from '_FIter std::lower_bound(_FIter, _FIter, const _Tp&, _Compare) [with _FIter = std::_List_iterator<A*>, _Tp = A*, _Compare = std::tr1::_Bind<std::tr1::_Mem_fn<bool (B::*)(A*, A*)>(std::tr1::_Placeholder<1>, std::tr1::_Placeholder<2>)>]'
..\bindTest\/b.h:13: instantiated from here
c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/tr1_impl/functional:1137: error: no match for call to '(std::tr1::_Mem_fn<bool (B::*)(A*, A*)>) (A*&, A* const&)'
c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/tr1_impl/functional:546: note: candidates are: _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class&, _ArgTypes ...) const [with _Res = bool, _Class = B, _ArgTypes = A*, A*]
c:\qt\2010.04\mingw\bin\../lib/gcc/mingw32/4.4.0/include/c++/tr1_impl/functional:551: note: _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class*, _ArgTypes ...) const [with _Res = bool, _Class = B, _ArgTypes = A*, A*]
aComp is a nonstatic member function of B, so you need to bind to the this pointer as well:
tr1::bind(&B::aComp, this, tr1::placeholders::_1, tr1::placeholders::_2)
Related
How do I get this to compile:
#include <functional>
#include <iostream>
#include <memory>
#include <string>
inline void print(std::string string1, std::string* string2)
{
std::cout << string1 << " " << string2 << std::endl;
delete string2;
}
class class1
{
public:
std::string foo{"Hello"};
std::shared_ptr<std::string> foo2;
class1();
};
class1::class1()
{
auto boundFunc = std::bind(print, foo, std::placeholders::_2);
foo2 = std::shared_ptr<std::string>(new std::string("world"), boundFunc);
}
int main()
{
class1 test;
}
GCC gives a long and cryptic bunch of error messages:
g++ -std=c++17 -o bind bind.cpp
In file included from /usr/include/c++/7.3.1/bits/shared_ptr.h:52:0,
from /usr/include/c++/7.3.1/memory:81,
from bind.cpp:21:
/usr/include/c++/7.3.1/bits/shared_ptr_base.h: In instantiation of ‘std::__shared_ptr<_Tp, _Lp>::__shared_ptr(_Yp*, _Deleter) [with _Yp = std::__cxx11::basic_string<char>; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; <template-parameter-2-3> = void; _Tp = std::__cxx11::basic_string<char>; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2]’:
/usr/include/c++/7.3.1/bits/shared_ptr.h:147:48: required from ‘std::shared_ptr<_Tp>::shared_ptr(_Yp*, _Deleter) [with _Yp = std::__cxx11::basic_string<char>; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; <template-parameter-2-3> = void; _Tp = std::__cxx11::basic_string<char>]’
bind.cpp:41:76: required from here
/usr/include/c++/7.3.1/bits/shared_ptr_base.h:1090:4: error: static assertion failed: deleter expression d(p) is well-formed
static_assert(__is_invocable<_Deleter&, _Yp*&>::value,
^~~~~~~~~~~~~
/usr/include/c++/7.3.1/bits/shared_ptr_base.h: In instantiation of ‘std::__shared_count<_Lp>::__shared_count(_Ptr, _Deleter, _Alloc) [with _Ptr = std::__cxx11::basic_string<char>*; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; _Alloc = std::allocator<void>; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2]’:
/usr/include/c++/7.3.1/bits/shared_ptr_base.h:605:57: required from ‘std::__shared_count<_Lp>::__shared_count(_Ptr, _Deleter) [with _Ptr = std::__cxx11::basic_string<char>*; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2]’
/usr/include/c++/7.3.1/bits/shared_ptr_base.h:1088:48: required from ‘std::__shared_ptr<_Tp, _Lp>::__shared_ptr(_Yp*, _Deleter) [with _Yp = std::__cxx11::basic_string<char>; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; <template-parameter-2-3> = void; _Tp = std::__cxx11::basic_string<char>; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2]’
/usr/include/c++/7.3.1/bits/shared_ptr.h:147:48: required from ‘std::shared_ptr<_Tp>::shared_ptr(_Yp*, _Deleter) [with _Yp = std::__cxx11::basic_string<char>; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; <template-parameter-2-3> = void; _Tp = std::__cxx11::basic_string<char>]’
bind.cpp:41:76: required from here
/usr/include/c++/7.3.1/bits/shared_ptr_base.h:623:11: error: no match for call to ‘(std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>) (std::__cxx11::basic_string<char>*&)’
__d(__p); // Call _Deleter on __p.
~~~^~~~~
In file included from bind.cpp:19:0:
/usr/include/c++/7.3.1/functional:547:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args)
^~~~~~~~
/usr/include/c++/7.3.1/functional:547:2: note: template argument deduction/substitution failed:
/usr/include/c++/7.3.1/functional:558:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args) const
^~~~~~~~
/usr/include/c++/7.3.1/functional:558:2: note: template argument deduction/substitution failed:
/usr/include/c++/7.3.1/functional:576:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) volatile [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args) volatile
^~~~~~~~
/usr/include/c++/7.3.1/functional:576:2: note: template argument deduction/substitution failed:
/usr/include/c++/7.3.1/functional:588:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const volatile [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args) const volatile
^~~~~~~~
/usr/include/c++/7.3.1/functional:588:2: note: template argument deduction/substitution failed:
In file included from /usr/include/c++/7.3.1/bits/shared_ptr.h:52:0,
from /usr/include/c++/7.3.1/memory:81,
from bind.cpp:21:
/usr/include/c++/7.3.1/bits/shared_ptr_base.h: In instantiation of ‘void std::_Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp>::_M_dispose() [with _Ptr = std::__cxx11::basic_string<char>*; _Deleter = std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>; _Alloc = std::allocator<void>; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2]’:
bind.cpp:47:1: required from here
/usr/include/c++/7.3.1/bits/shared_ptr_base.h:470:25: error: no match for call to ‘(std::_Bind<void (*(std::__cxx11::basic_string<char>, std::_Placeholder<2>))(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*)>) (std::__cxx11::basic_string<char>*&)’
{ _M_impl._M_del()(_M_impl._M_ptr); }
~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
In file included from bind.cpp:19:0:
/usr/include/c++/7.3.1/functional:547:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args)
^~~~~~~~
/usr/include/c++/7.3.1/functional:547:2: note: template argument deduction/substitution failed:
/usr/include/c++/7.3.1/functional:558:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args) const
^~~~~~~~
/usr/include/c++/7.3.1/functional:558:2: note: template argument deduction/substitution failed:
/usr/include/c++/7.3.1/functional:576:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) volatile [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args) volatile
^~~~~~~~
/usr/include/c++/7.3.1/functional:576:2: note: template argument deduction/substitution failed:
/usr/include/c++/7.3.1/functional:588:2: note: candidate: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const volatile [with _Args = {_Args ...}; _Result = _Result; _Functor = void (*)(std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>*); _Bound_args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::_Placeholder<2>}]
operator()(_Args&&... __args) const volatile
^~~~~~~~
/usr/include/c++/7.3.1/functional:588:2: note: template argument deduction/substitution failed:
I'm not sure what to make of this output, and I haven't found any good documentation of std::bind which provides examples for all the various ways in which it might be used, only the most basic cases.
stackoverflow wants more details, but I don't even know what else to provide. It should be obvious from the code what the problem is. If I knew what to say I would be able to search for it already, but I'm not sure how to describe this problem.
Simple fix: Replace
auto boundFunc = std::bind(print, foo, std::placeholders::_2);
with
auto boundFunc = std::bind(print, foo, std::placeholders::_1);
Why?
In std::bind, the placeholders indicate the index of the argument to the result function. std::placeholders::_1 means "use the first argument passed to me in this position".
When you pass std::placeholders::_2, your boundFunc will take the wrong number of arguments (2 instead of 1) and no longer be a valid deleter for an std::shared_ptr.
The error is subtle but there. You probably used std::placeholders::_2 because you are using the second argument, right? Well, that's not how you use them.
The number _N designates that the argument number N (when you call the result) is bound to _N. In other words, you need to enumerate them from 1 onwards in your case:
auto boundFunc = std::bind(print, foo, std::placeholders::_1);
// ^
Before people start telling me to do a google search for my problem, let me say I've been trying for quite a while.
I can't figure out how to pass an object by reference in C++, I keep getting a massive printout of compiler errors. I can include them if they would help. Specifically, I'm trying to pass the RSSFeed object feed by reference to the function parseFeed in a thread.
void parseFeed(RSSFeed& feed) {
//dostuff
}
RSSFeed feed();
thread(parseFeed, feed); // line 119
errors:
g++ -g -Wall -pedantic -O0 -std=c++0x -D_GLIBCXX_USE_NANOSLEEP -D_GLIBCXX_USE_SCHED_YIELD -I/usr/class/cs110/include/libxml2 -I/usr/class/cs110/local/include -c -o news-aggregator.o news-aggregator.cc
In file included from /usr/include/c++/4.6/functional:56:0,
from /usr/include/c++/4.6/bits/stl_algo.h:68,
from /usr/include/c++/4.6/algorithm:63,
from news-aggregator.cc:14:
rss-feed.h: In constructor âconstexpr std::_Head_base<_Idx, _Head, false>::_Head_base(const _Head&) [with long unsigned int _Idx = 0ul, _Head = RSSFeed]â:
/usr/include/c++/4.6/tuple:162:44: instantiated from âconstexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const _Head&, const _Tail& ...) [with long unsigned int _Idx = 0ul, _Head = RSSFeed, _Tail = {}]â
/usr/include/c++/4.6/tuple:423:24: instantiated from âconstexpr std::tuple<_T1>::tuple(const _T1&) [with _T1 = RSSFeed]â
/usr/include/c++/4.6/functional:1362:70: instantiated from âstd::_Bind_result<_Result, _Functor(_Bound_args ...)>::_Bind_result(_Functor&&, _Args&& ...) [with _Args = {RSSFeed&}, _Result = void, _Functor = void (*)(RSSFeed&), _Bound_args = {RSSFeed}]â
/usr/include/c++/4.6/functional:1477:41: instantiated from âtypename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type std::bind(_Functor&&, _ArgTypes&& ...) [with _Result = void, _Functor = void (&)(RSSFeed&), _ArgTypes = {RSSFeed&}, typename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type = std::_Bind_result<void, void (*(RSSFeed))(RSSFeed&)>]â
/usr/include/c++/4.6/thread:135:9: instantiated from âstd::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(RSSFeed&), _Args = {RSSFeed&}]â
news-aggregator.cc:119:25: instantiated from here
rss-feed.h:54:3: error: âRSSFeed::RSSFeed(const RSSFeed&)â is private
/usr/include/c++/4.6/tuple:97:25: error: within this context
/usr/include/c++/4.6/tuple:97:25: error: use of deleted function âRSSFeed::RSSFeed(const RSSFeed&)â
rss-feed.h:54:3: error: declared here
rss-feed.h: In constructor âstd::_Head_base<_Idx, _Head, false>::_Head_base(_UHead&&) [with _UHead = RSSFeed, long unsigned int _Idx = 0ul, _Head = RSSFeed]â:
/usr/include/c++/4.6/tuple:174:43: instantiated from âstd::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(std::_Tuple_impl<_Idx, _Head, _Tail ...>&&) [with long unsigned int _Idx = 0ul, _Head = RSSFeed, _Tail = {}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<0ul, RSSFeed>]â
/usr/include/c++/4.6/tuple:434:51: instantiated from âstd::tuple<_T1>::tuple(std::tuple<_T1>&&) [with _T1 = RSSFeed, std::tuple<_T1> = std::tuple<RSSFeed>]â
/usr/include/c++/4.6/functional:1368:78: instantiated from âstd::_Bind_result<_Result, _Functor(_Bound_args ...)>::_Bind_result(std::_Bind_result<_Result, _Functor(_Bound_args ...)>&&) [with _Result = void, _Functor = void (*)(RSSFeed&), _Bound_args = {RSSFeed}, std::_Bind_result<_Result, _Functor(_Bound_args ...)> = std::_Bind_result<void, void (*(RSSFeed))(RSSFeed&)>]â
/usr/include/c++/4.6/functional:1477:41: instantiated from âtypename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type std::bind(_Functor&&, _ArgTypes&& ...) [with _Result = void, _Functor = void (&)(RSSFeed&), _ArgTypes = {RSSFeed&}, typename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type = std::_Bind_result<void, void (*(RSSFeed))(RSSFeed&)>]â
/usr/include/c++/4.6/thread:135:9: instantiated from âstd::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(RSSFeed&), _Args = {RSSFeed&}]â
news-aggregator.cc:119:25: instantiated from here
rss-feed.h:54:3: error: âRSSFeed::RSSFeed(const RSSFeed&)â is private
/usr/include/c++/4.6/tuple:101:42: error: within this context
/usr/include/c++/4.6/tuple:101:42: error: use of deleted function âRSSFeed::RSSFeed(const RSSFeed&)â
rss-feed.h:54:3: error: declared here
Resolved:
thread(parseFeed, ref( feed ) ); // line 119
This
RSSFeed feed();
is a function declaration that returns an object of type RSSFeed and has no parameters. It is not an object definition.
Write instead
RSSFeed feed;
Also it seems from the list of error messages that class RSSFeed has no the copy constructor that is it is defined as deleted.
#include <vector>
class B {
};
class A {
const std::vector<B> m_v;
public:
A(const std::vector<B>& v) : m_v(v) {}
void doSomething() {}
};
void foo(void* bar) {
A* a = (A*)bar;
a->doSomething();
}
int main() {
std::vector<B> v;
std::vector<A > l;
for (auto i = 0; i < 10; i++) {
A a(v);
l.push_back(std::move(a));
foo((void*)&l[i]);
}
return 0;
}
$ g++ -Wall initList.cpp -o initList -lrt -O3 -std=c++0x
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/vector:70:0,
from initList.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc: In member function \u2018void std::vector::_M_insert_aux(std::vector::iterator, _Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator, std::vector::iterator = __gnu_cxx::__normal_iterator >, typename std::_Vector_base::_Tp_alloc_type::pointer = A*]`:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:102:4: instantiated from \u2018void std::vector::emplace_back(_Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_vector.h:840:9: instantiated from \u2018void std::vector::push_back(std::vector::value_type&&) [with _Tp = A, _Alloc = std::allocator, std::vector::value_type = A]`
initList.cpp:23:27: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:319:4: error: use of deleted function '& A::operator=(const A&)`
initList.cpp:6:7: error: '& A::operator=(const A&)` is implicitly deleted because the default definition would be ill-formed:
initList.cpp:6:7: error: passing \u2018const std::vector` as \u2018this` argument of \u2018std::vector& std::vector::operator=(const std::vector&) [with _Tp = B, _Alloc = std::allocator]` discards qualifiers [-fpermissive]
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/vector:61:0,
from initList.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h: In static member function \u2018static _BI2 std::__copy_move_backward::__copy_move_b(_BI1, _BI1, _BI2) [with _BI1 = A*, _BI2 = A*]`:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:581:18: instantiated from \u2018_BI2 std::__copy_move_backward_a(_BI1, _BI1, _BI2) [with bool _IsMove = true, _BI1 = A*, _BI2 = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:590:34: instantiated from \u2018_BI2 std::__copy_move_backward_a2(_BI1, _BI1, _BI2) [with bool _IsMove = true, _BI1 = A*, _BI2 = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:661:15: instantiated from \u2018_BI2 std::move_backward(_BI1, _BI1, _BI2) [with _BI1 = A*, _BI2 = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:313:4: instantiated from \u2018void std::vector::_M_insert_aux(std::vector::iterator, _Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator, std::vector::iterator = __gnu_cxx::__normal_iterator >, typename std::_Vector_base::_Tp_alloc_type::pointer = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:102:4: instantiated from \u2018void std::vector::emplace_back(_Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_vector.h:840:9: instantiated from \u2018void std::vector::push_back(std::vector::value_type&&) [with _Tp = A, _Alloc = std::allocator, std::vector::value_type = A]`
initList.cpp:23:27: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:546:6: error: use of deleted function '& A::operator=(const A&)`
If I don't specify const for m_v. It compiles fine.
The error suggests something with assign operator, which I don't see how it is invoked.
Any idea?
Thanks in advance.
It's a bug in older versions of GCC/libstdc++, your code compiles fine with GCC 4.8.1. Live example. The bug is triggered by
l.push_back(std::move(a));
as older versions of GCC tried to create a default-constructed element in the vector and assigned the parameter std::move(a) to it in a second step instead of using the in-place copy/move-ctor.
I have this minimal not-working example of code
#include <future>
int main()
{
auto intTask = std::packaged_task<int()>( []()->int{ return 5; } );
std::packaged_task<void()> voidTask{ std::move(intTask) };
}
Why doesn't it compile (on gcc 4.8.1)? I suspect, the reason is, that std::packaged_task stores the lambda internally inside an std::function which needs a CopyConstructible argument. However, std::packaged_task is move-only. Is this a bug? What does the standard say about it? In my opinion std::packaged_task should not need a CopyConstructible argument, but a MoveConstructible argument should be enough.
By the way, when I replace std::packaged_task<int()> by std::packaged_task<void()> everything compiles fine.
GCC 4.8.1 is giving me this error message:
In file included from /usr/include/c++/4.6/future:38:0,
from ../cpp11test/main.cpp:160:
/usr/include/c++/4.6/functional: In static member function 'static void std::_Function_base::_Base_manager<_Functor>::_M_clone(std::_Any_data&, const std::_Any_data&, std::false_type) [with _Functor = std::packaged_task<int()>, std::false_type = std::integral_constant<bool, false>]':
/usr/include/c++/4.6/functional:1652:8: instantiated from 'static bool std::_Function_base::_Base_manager<_Functor>::_M_manager(std::_Any_data&, const std::_Any_data&, std::_Manager_operation) [with _Functor = std::packaged_task<int()>]'
/usr/include/c++/4.6/functional:2149:6: instantiated from 'std::function<_Res(_ArgTypes ...)>::function(_Functor, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type) [with _Functor = std::packaged_task<int()>, _Res = void, _ArgTypes = {}, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type = std::function<void()>::_Useless]'
/usr/include/c++/4.6/bits/shared_ptr_base.h:410:4: instantiated from 'std::_Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp>::_Sp_counted_ptr_inplace(_Alloc, _Args&& ...) [with _Args = {std::packaged_task<int()>}, _Tp = std::__future_base::_Task_state<void()>, _Alloc = std::allocator<std::__future_base::_Task_state<void()> >, __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]'
/usr/include/c++/4.6/bits/shared_ptr_base.h:518:8: instantiated from 'std::__shared_count<_Lp>::__shared_count(std::_Sp_make_shared_tag, _Tp*, const _Alloc&, _Args&& ...) [with _Tp = std::__future_base::_Task_state<void()>, _Alloc = std::allocator<std::__future_base::_Task_state<void()> >, _Args = {std::packaged_task<int()>}, __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]'
/usr/include/c++/4.6/bits/shared_ptr_base.h:987:35: instantiated from 'std::__shared_ptr<_Tp, _Lp>::__shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...) [with _Alloc = std::allocator<std::__future_base::_Task_state<void()> >, _Args = {std::packaged_task<int()>}, _Tp = std::__future_base::_Task_state<void()>, __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]'
/usr/include/c++/4.6/bits/shared_ptr.h:317:64: instantiated from 'std::shared_ptr<_Tp>::shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...) [with _Alloc = std::allocator<std::__future_base::_Task_state<void()> >, _Args = {std::packaged_task<int()>}, _Tp = std::__future_base::_Task_state<void()>]'
/usr/include/c++/4.6/bits/shared_ptr.h:535:39: instantiated from 'std::shared_ptr<_Tp> std::allocate_shared(const _Alloc&, _Args&& ...) [with _Tp = std::__future_base::_Task_state<void()>, _Alloc = std::allocator<std::__future_base::_Task_state<void()> >, _Args = {std::packaged_task<int()>}]'
/usr/include/c++/4.6/bits/shared_ptr.h:551:42: instantiated from 'std::shared_ptr<_Tp1> std::make_shared(_Args&& ...) [with _Tp = std::__future_base::_Task_state<void()>, _Args = {std::packaged_task<int()>}]'
/usr/include/c++/4.6/future:1223:66: instantiated from 'std::packaged_task<_Res(_ArgTypes ...)>::packaged_task(_Fn&&) [with _Fn = std::packaged_task<int()>, _Res = void, _ArgTypes = {}]'
../cpp11test/main.cpp:165:61: instantiated from here
/usr/include/c++/4.6/functional:1616:4: error: use of deleted function 'std::packaged_task<_Res(_ArgTypes ...)>::packaged_task(std::packaged_task<_Res(_ArgTypes ...)>&) [with _Res = int, _ArgTypes = {}, std::packaged_task<_Res(_ArgTypes ...)> = std::packaged_task<int()>]'
/usr/include/c++/4.6/future:1244:7: error: declared here
UPDATE: I have written the following test program. It seems to support the assumption that the reason is missing CopyConstructability. Again, what are the requirements on the type of the object from which an std::packaged_task may be constructed?
#include <future>
struct Functor {
Functor() {}
Functor( const Functor & ) {} // without this line it doesn't compile
Functor( Functor && ) {}
int operator()(){ return 5; }
};
int main() {
auto intTask = std::packaged_task<int()>( Functor{} );
}
Indeed, packaged_task only has a moving constructor (30.6.9/2):
template <class F> explicit packaged_task(F&& f);
However, your problem is the explicit constructor. So write it like this:
std::packaged_task<int()> pt([]() -> int { return 1; });
Complete example:
#include <future>
#include <thread>
int main()
{
std::packaged_task<int()> intTask([]() -> int { return 5; } );
auto f = intTask.get_future();
std::thread(std::move(intTask)).detach();
return f.get();
}
No. You just can't move a packaged_task<int ()> into a packaged_task<void ()>. These types a unrelated and cannot be move-assigned or move-constructed from each other. If you for some reason really want to do that you can "swallow" the result of the int () like this
The standard (as of N3690) doesn't state anything explicitly about the requirements of the type F in
template <class R, class... ArgTypes>
template <class F>
packaged_task<R(ArgTypes...)>::packaged_task(F&& f);
(see 30.6.9.1) However, it states that
Invoking a copy of f shall behave the same as invoking f.
and that this call can throw
any exceptions thrown by the copy or move constructor of f, or std::bad_alloc if memory
for the internal data structures could not be allocated.
This implicitly implies that the type F must be at least MoveConstructible, or CopyConstructible, if an lvalue reference is handed to the function.
Hence, it's not a bug, it's just not specified that precisely. To solve the problem of putting a std::packaged_task<int()> into a std::packaged_task<void()> just wrap the first into a shared_ptr like this:
#include <future>
#include <memory>
int main()
{
auto intTask = std::make_shared<std::packaged_task<int()>>(
[]()->int{ return 5; } );
std::packaged_task<void()> voidTask{ [=]{ (*intTask)(); } };
}
The purpose is to execute CVS890Executor::do_full_frame when calling the m_callback_fn within CDevVS890.
Following is the incriminated code:
"CDevVS890.h"
typedef std::tr1::function<void (void* frame, int len)> DoFrameFn;
class CDevVS890
{
public:
CDevVS890();
void receive();
DoFrameFn m_callback_fn;
}
"CDevVS890.cpp"
void CDevVS890::receive()
{
...
m_callback_fn((void*)frame, (int)len);
}
/*----------------------------------------------------------------------*/
"CVS890Executor.h"
class CVS890Executor
{
public:
CVS890Executor();
private:
void hookup_to_DevVS890();
void do_full_frame( void* frame, int len );
}
"CVS890Executor.cpp"
CVS890Executor::CVS890Executor()
{
hookup_to_DevVS890();
}
void CVS890Executor::hookup_to_DevVS890()
{
m_pDevVS890 = new CDevVS890();
m_pDevVS890->m_callback_fn =
std::tr1::bind(&CVS890Executor::do_full_frame, this, _1);
}
void CVS890Executor::do_full_frame(void* frame, int len)
{
...
}
The errors are multiple and very difficult to read:
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1/functional:56,
from ../../src/Common/CDevVS890.h:17,
from CVS890Executor.h:13,
from CVS890Executor.cpp:8:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional: In member function âtypename std::tr1::result_of<_Functor(typename std::tr1::result_of 0)>(_Bound_args, std::tr1::tuple<_UElements ...>)>::type ...)>::type std::tr1::_Bind<_Functor(_Bound_args ...)>::__call(const std::tr1::tuple<_UElements ...>&, std::tr1::_Index_tuple<_Indexes ...>) [with _Args = void*&, int&, int ..._Indexes = 0, 1, _Functor = std::tr1::_Mem_fn, _Bound_args = CVS890Executor*, std::tr1::_Placeholder<1>]â:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1191: instantiated from âtypename std::tr1::result_of<_Functor(typename std::tr1::result_of 0)>(_Bound_args, std::tr1::tuple<_UElements ...>)>::type ...)>::type std::tr1::_Bind<_Functor(_Bound_args ...)>::operator()(_Args& ...) [with _Args = void*, int, _Functor = std::tr1::_Mem_fn, _Bound_args = CVS890Executor*, std::tr1::_Placeholder<1>]â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1668: instantiated from âstatic void std::tr1::_Function_handler::_M_invoke(const std::tr1::_Any_data&, _ArgTypes ...) [with _Functor = std::tr1::_Bind(CVS890Executor*, std::tr1::_Placeholder<1>)>, _ArgTypes = void*, int]â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:2005: instantiated from âstd::tr1::function<_Res(_ArgTypes ...)>::function(_Functor, typename __gnu_cxx::__enable_if<(! std::tr1::is_integral::value), std::tr1::function<_Res(_ArgTypes ...)>::Useless>::_type) [with _Functor = std::tr1::_Bind(CVS890Executor*, std::tr1::_Placeholder<1>)>, _Res = void, _ArgTypes = void*, int]â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1885: instantiated from âtypename __gnu_cxx::__enable_if<(! std::tr1::is_integral::value), std::tr1::function<_Res(ArgTypes ...)>&>::_type std::tr1::function<_Res(_ArgTypes ...)>::operator=(_Functor) [with _Functor = std::tr1::_Bind(CVS890Executor*, std::tr1::_Placeholder<1>)>, _Res = void, _ArgTypes = void*, int]â
CVS890Executor.cpp:115: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1137: error: no match for call to â(std::tr1::_Mem_fn) (CVS890Executor*&, void*&)â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:546: note: candidates are: _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class&, _ArgTypes ...) const [with _Res = void, _Class = CVS890Executor, _ArgTypes = void*, int]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:551: note: _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class*, _ArgTypes ...) const [with _Res = void, _Class = CVS890Executor, _ArgTypes = void*, int]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1137: error: return-statement with a value, in function returning 'void'
make: * [CVS890Executor.o] Error 1
Any idea what's wrong with this?
Cheers
You forgot about the second argument. Your call of bind function should be like this:
std::tr1::bind(&CVS890Executor::do_full_frame, this, _1, _2);
// ^^
In CVS890Executor::hookup_to_DevVS890(), you are not binding any arguments to the member function do_full_frame.
You are also trying to assign the return value of the function to m_callback_fn but do_full_frame() is declared to return void (no return value).