[英]Why the following code compiles with `c++03` but not with `c++11`
I am using the boost::python
library in this tiny mwe.我在这个小小的 mwe 中使用了
boost::python
库。
#include <deque>
#include <boost/python.hpp>
typedef std::deque<long unsigned int> DequeUInt64;
BOOST_PYTHON_MODULE_INIT(tmp) {
boost::python::class_<DequeUInt64>("DequeUInt64")
.def("push_back" ,&DequeUInt64::push_back)
.def("push_front" ,&DequeUInt64::push_front);
}
I observed that the code above compiles with std=c++03
and gnu++03
but not with c++11
or c++0x
.我观察到上面的代码使用
std=c++03
和gnu++03
编译,但不使用c++11
或c++0x
。 The error is:错误是:
tmp.cpp: In function 'void init_module_tmp()':
tmp.cpp:8:47: error: no matching function for call to 'boost::python::class_<std::deque<long unsigned int> >::def(const char [10], <unresolved overloaded function type>)'
.def("push_back" ,&DequeUInt64::push_back)
^
In file included [from /opt/local/include/boost/python.hpp:18:0], [from tmp.cpp:2]:
/opt/local/include/boost/python/class.hpp:223:11:
note: candidate:
template<class Derived> boost::python::class_<T, X1, X2, X3>::self&
boost::python::class_<T, X1, X2, X3>::def(const boost::python::def_visitor<Derived>&)
[with Derived = Derived;
W = std::deque<long unsigned int>;
X1 = boost::python::detail::not_specified;
X2 = boost::python::detail::not_specified;
X3 = boost::python::detail::not_specified]
self& def(def_visitor<Derived> const& visitor)
^
note: template argument deduction/substitution failed:
tmp.cpp:8:47:
note: mismatched types 'const boost::python::def_visitor<U>' and 'const char [10]'
.def("push_back" ,&DequeUInt64::push_back)
^
In file included [from /opt/local/include/boost/python.hpp:18:0], [from tmp.cpp:2]:
/opt/local/include/boost/python/class.hpp:233:11:
note: candidate:
template<class F> boost::python::class_<T, X1, X2, X3>::self&
boost::python::class_<T, X1, X2, X3>::def(const char*, F)
[with F = F;
W = std::deque<long unsigned int>;
X1 = boost::python::detail::not_specified;
X2 = boost::python::detail::not_specified;
X3 = boost::python::detail::not_specified]
self& def(char const* name, F f)
^
note: template argument deduction/substitution failed:
tmp.cpp:8:47:
note: couldn't deduce template parameter 'F'
.def("push_back" ,&DequeUInt64::push_back)
My boost is boost: stable 1.60.0
and my g++ is g++-mp-5 (MacPorts gcc5 5.4.0_0) 5.4.0
.我的提升是
boost: stable 1.60.0
而我的 g++ 是g++-mp-5 (MacPorts gcc5 5.4.0_0) 5.4.0
。 I can see that somehow the newer standard is causing problems with type/template inference but honestly I don't really understand why?我可以看到更新的标准以某种方式导致类型/模板推断出现问题,但老实说我真的不明白为什么? Is the problem because Boost is simply not tested with c++11?
问题是因为 Boost 根本没有用 c++11 测试吗? What exactly does the error message above mean anyway?
无论如何,上面的错误消息到底是什么意思?
The error message gives you a clue:错误消息为您提供了一个线索:
unresolved overloaded function type
未解决的重载函数类型
You pass in std::deque::push_back
.你传入
std::deque::push_back
。 Looking at a reference , you can see there are two overloads:查看参考,您可以看到有两个重载:
void push_back( const T& value );
void push_back( T&& value ); // (since C++11)
C++11 added a new overload. C++11 添加了一个新的重载。 Therefore, passing a pointer to this as an argument becomes invalid.
因此,将指向 this 的指针作为参数传递变得无效。 Likewise for
push_front
.同样对于
push_front
。 Note that even before C++11, implementations are allowed to add their own overloads [citation needed] .请注意,即使在 C++11 之前,也允许实现添加自己的重载[需要引用] 。
You can cast it to the appropriate type:您可以将其转换为适当的类型:
.def("push_back" ,static_cast<void(DequeUInt64::*)(DequeUInt64::const_reference)>(&DequeUInt64::push_back))
.def("push_front" ,static_cast<void(DequeUInt64::*)(DequeUInt64::const_reference)>(&DequeUInt64::push_front))
I cast it rather than specify the template argument explicitly per STL's Don't Help the Compiler talk.我强制转换而不是根据 STL 的Don't Help the Compiler talk 明确指定模板参数。
You can also use a lambda if you force it to a function pointer first, per Tanner's comment:根据 Tanner 的评论,如果先将 lambda 强制为函数指针,也可以使用 lambda:
.def("push_back" ,+[](DequeUInt64* d, DequeUInt64::const_reference x) { return d->push_back(x); })
.def("push_front" ,+[](DequeUInt64* d, DequeUInt64::const_reference x) { return d->push_front(x); })
The problem is that C++11 added an overload to push_back
to support move semantics ie void push_front( T&& value );
问题是 C++11 给
push_back
添加了一个重载来支持移动语义,即void push_front( T&& value );
So the compiler doesn't know which one to pick ( <unresolved overloaded function type>
).所以编译器不知道选择哪一个(
<unresolved overloaded function type>
)。 You have to spell it out, like this:你必须把它拼出来,像这样:
boost::python::class_<DequeUInt64>("DequeUInt64")
.def<void (DequeUInt64::*)( const T&)>("push_back",&DequeUInt64::push_back)
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